png.c File Reference

#include "pngpriv.h"

Include dependency graph for png.c:

Macros
#define	APPEND_STRING(string)   pos = png_safecat(out, 29, pos, (string))
#define	APPEND_NUMBER(format, value)   APPEND_STRING(PNG_FORMAT_NUMBER(number_buf, format, (value)))
#define	APPEND(ch)   if (pos < 28) out[pos++] = (ch)
#define	PNG_MD5(a, b, c, d)   { a, b, c, d }, (a!=0)||(b!=0)||(c!=0)||(d!=0)
#define	PNG_ICC_CHECKSUM(adler, crc, md5, intent, broke, date, length, fname)   { adler, crc, length, md5, broke, intent },
#define	png_gt(a, b)   ((a) > (b))
#define	png_fp_add(state, flags)   ((state) |= (flags))
#define	png_fp_set(state, value)   ((state) = (value) | ((state) & PNG_FP_STICKY))

Typedefs
typedef png_libpng_version_1_6_16	Your_png_h_is_not_version_1_6_16

Functions
void	png_set_sig_bytes (png_structrp png_ptr, int num_bytes)
int	png_sig_cmp (png_const_bytep sig, png_size_t start, png_size_t num_to_check)
voidpf	png_zalloc (voidpf png_ptr, uInt items, uInt size)
void	png_zfree (voidpf png_ptr, voidpf ptr)
void	png_reset_crc (png_structrp png_ptr)
void	png_calculate_crc (png_structrp png_ptr, png_const_bytep ptr, png_size_t length)
int	png_user_version_check (png_structrp png_ptr, png_const_charp user_png_ver)
png_structp	png_create_png_struct (png_const_charp user_png_ver, png_voidp error_ptr, png_error_ptr error_fn, png_error_ptr warn_fn, png_voidp mem_ptr, png_malloc_ptr malloc_fn, png_free_ptr free_fn)
png_infop	png_create_info_struct (png_const_structrp png_ptr)
void	png_destroy_info_struct (png_const_structrp png_ptr, png_infopp info_ptr_ptr)
void	png_info_init_3 (png_infopp ptr_ptr, png_size_t png_info_struct_size)
void	png_data_freer (png_const_structrp png_ptr, png_inforp info_ptr, int freer, png_uint_32 mask)
void	png_free_data (png_const_structrp png_ptr, png_inforp info_ptr, png_uint_32 mask, int num)
png_voidp	png_get_io_ptr (png_const_structrp png_ptr)
void	png_init_io (png_structrp png_ptr, png_FILE_p fp)
void	png_save_int_32 (png_bytep buf, png_int_32 i)
int	png_convert_to_rfc1123_buffer (char out[29], png_const_timep ptime)
png_const_charp	png_convert_to_rfc1123 (png_structrp png_ptr, png_const_timep ptime)
png_const_charp	png_get_copyright (png_const_structrp png_ptr)
png_const_charp	png_get_libpng_ver (png_const_structrp png_ptr)
png_const_charp	png_get_header_ver (png_const_structrp png_ptr)
png_const_charp	png_get_header_version (png_const_structrp png_ptr)
void	png_build_grayscale_palette (int bit_depth, png_colorp palette)
int	png_handle_as_unknown (png_const_structrp png_ptr, png_const_bytep chunk_name)
int	png_chunk_unknown_handling (png_const_structrp png_ptr, png_uint_32 chunk_name)
int	png_reset_zstream (png_structrp png_ptr)
png_uint_32	png_access_version_number (void)
void	png_zstream_error (png_structrp png_ptr, int ret)
static int	png_colorspace_check_gamma (png_const_structrp png_ptr, png_colorspacerp colorspace, png_fixed_point gAMA, int from)
void	png_colorspace_set_gamma (png_const_structrp png_ptr, png_colorspacerp colorspace, png_fixed_point gAMA)
void	png_colorspace_sync_info (png_const_structrp png_ptr, png_inforp info_ptr)
void	png_colorspace_sync (png_const_structrp png_ptr, png_inforp info_ptr)
static int	png_xy_from_XYZ (png_xy *xy, const png_XYZ *XYZ)
static int	png_XYZ_from_xy (png_XYZ *XYZ, const png_xy *xy)
static int	png_XYZ_normalize (png_XYZ *XYZ)
static int	png_colorspace_endpoints_match (const png_xy *xy1, const png_xy *xy2, int delta)
static int	png_colorspace_check_xy (png_XYZ *XYZ, const png_xy *xy)
static int	png_colorspace_check_XYZ (png_xy *xy, png_XYZ *XYZ)
static int	png_colorspace_set_xy_and_XYZ (png_const_structrp png_ptr, png_colorspacerp colorspace, const png_xy *xy, const png_XYZ *XYZ, int preferred)
int	png_colorspace_set_chromaticities (png_const_structrp png_ptr, png_colorspacerp colorspace, const png_xy *xy, int preferred)
int	png_colorspace_set_endpoints (png_const_structrp png_ptr, png_colorspacerp colorspace, const png_XYZ *XYZ_in, int preferred)
static char	png_icc_tag_char (png_uint_32 byte)
static void	png_icc_tag_name (char *name, png_uint_32 tag)
static int	is_ICC_signature_char (png_alloc_size_t it)
static int	is_ICC_signature (png_alloc_size_t it)
static int	png_icc_profile_error (png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_alloc_size_t value, png_const_charp reason)
int	png_colorspace_set_sRGB (png_const_structrp png_ptr, png_colorspacerp colorspace, int intent)
int	png_icc_check_length (png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_uint_32 profile_length)
int	png_icc_check_header (png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_uint_32 profile_length, png_const_bytep profile, int color_type)
int	png_icc_check_tag_table (png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_uint_32 profile_length, png_const_bytep profile)
static int	png_compare_ICC_profile_with_sRGB (png_const_structrp png_ptr, png_const_bytep profile, uLong adler)
void	png_icc_set_sRGB (png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_bytep profile, uLong adler)
int	png_colorspace_set_ICC (png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_uint_32 profile_length, png_const_bytep profile, int color_type)
void	png_colorspace_set_rgb_coefficients (png_structrp png_ptr)
void	png_check_IHDR (png_const_structrp png_ptr, png_uint_32 width, png_uint_32 height, int bit_depth, int color_type, int interlace_type, int compression_type, int filter_type)
int	png_check_fp_number (png_const_charp string, png_size_t size, int *statep, png_size_tp whereami)
int	png_check_fp_string (png_const_charp string, png_size_t size)
static double	png_pow10 (int power)
void	png_ascii_from_fp (png_const_structrp png_ptr, png_charp ascii, png_size_t size, double fp, unsigned int precision)
void	png_ascii_from_fixed (png_const_structrp png_ptr, png_charp ascii, png_size_t size, png_fixed_point fp)
png_fixed_point	png_fixed (png_const_structrp png_ptr, double fp, png_const_charp text)
int	png_muldiv (png_fixed_point_p res, png_fixed_point a, png_int_32 times, png_int_32 divisor)
png_fixed_point	png_muldiv_warn (png_const_structrp png_ptr, png_fixed_point a, png_int_32 times, png_int_32 divisor)
png_fixed_point	png_reciprocal (png_fixed_point a)
int	png_gamma_significant (png_fixed_point gamma_val)
static png_fixed_point	png_product2 (png_fixed_point a, png_fixed_point b)
png_fixed_point	png_reciprocal2 (png_fixed_point a, png_fixed_point b)
png_byte	png_gamma_8bit_correct (unsigned int value, png_fixed_point gamma_val)
png_uint_16	png_gamma_16bit_correct (unsigned int value, png_fixed_point gamma_val)
png_uint_16	png_gamma_correct (png_structrp png_ptr, unsigned int value, png_fixed_point gamma_val)
static void	png_build_16bit_table (png_structrp png_ptr, png_uint_16pp *ptable, const unsigned int shift, const png_fixed_point gamma_val)
static void	png_build_16to8_table (png_structrp png_ptr, png_uint_16pp *ptable, const unsigned int shift, const png_fixed_point gamma_val)
static void	png_build_8bit_table (png_structrp png_ptr, png_bytepp ptable, const png_fixed_point gamma_val)
void	png_destroy_gamma_table (png_structrp png_ptr)
void	png_build_gamma_table (png_structrp png_ptr, int bit_depth)
int	png_set_option (png_structrp png_ptr, int option, int onoff)
static int	png_image_free_function (png_voidp argument)
void	png_image_free (png_imagep image)
int	png_image_error (png_imagep image, png_const_charp error_message)

Variables
static const png_xy	sRGB_xy
static const png_byte	D50_nCIEXYZ [12]
struct {
png_uint_32   adler
png_uint_32   crc
png_uint_32   length
png_uint_32   md5 [4]
png_byte   have_md5
png_byte   is_broken
png_uint_16   intent
}	png_sRGB_checks []
const png_uint_16	png_sRGB_table [256]
const png_uint_16	png_sRGB_base [512]
const png_byte	png_sRGB_delta [512]

Macro Definition Documentation

#define APPEND_STRING

(

string

)

pos = png_safecat(out, 29, pos, (string))

#define APPEND_NUMBER	(		format,
			value
	)		APPEND_STRING(PNG_FORMAT_NUMBER(number_buf, format, (value)))

#define APPEND

(

ch

)

if (pos < 28) out[pos++] = (ch)

#define PNG_MD5	(		a,
			b,
			c,
			d
	)		{ a, b, c, d }, (a!=0)||(b!=0)||(c!=0)||(d!=0)

#define PNG_ICC_CHECKSUM	(		adler,
			crc,
			md5,
			intent,
			broke,
			date,
			length,
			fname
	)		{ adler, crc, length, md5, broke, intent },

#define png_gt	(		a,
			b
	)		((a) > (b))

#define png_fp_add	(		state,
			flags
	)		((state) |= (flags))

#define png_fp_set	(		state,
			value
	)		((state) = (value) | ((state) & PNG_FP_STICKY))

Typedef Documentation

typedef png_libpng_version_1_6_16 Your_png_h_is_not_version_1_6_16

Function Documentation

void png_set_sig_bytes	(	png_structrp	png_ptr,
		int	num_bytes
	)

{
   png_debug(1, "in png_set_sig_bytes");

   if (png_ptr == NULL)
      return;

   if (num_bytes > 8)
      png_error(png_ptr, "Too many bytes for PNG signature");

   png_ptr->sig_bytes = (png_byte)(num_bytes < 0 ? 0 : num_bytes);
}

int png_sig_cmp	(	png_const_bytep	sig,
		png_size_t	start,
		png_size_t	num_to_check
	)

{
   png_byte png_signature[8] = {137, 80, 78, 71, 13, 10, 26, 10};

   if (num_to_check > 8)
      num_to_check = 8;

   else if (num_to_check < 1)
      return (-1);

   if (start > 7)
      return (-1);

   if (start + num_to_check > 8)
      num_to_check = 8 - start;

   return ((int)(memcmp(&sig[start], &png_signature[start], num_to_check)));
}

voidpf png_zalloc	(	voidpf	png_ptr,
		uInt	items,
		uInt	size
	)

{
   png_alloc_size_t num_bytes = size;

   if (png_ptr == NULL)
      return NULL;

   if (items >= (~(png_alloc_size_t)0)/size)
   {
      png_warning (png_voidcast(png_structrp, png_ptr),
         "Potential overflow in png_zalloc()");
      return NULL;
   }

   num_bytes *= items;
   return png_malloc_warn(png_voidcast(png_structrp, png_ptr), num_bytes);
}

void png_zfree	(	voidpf	png_ptr,
		voidpf	ptr
	)

{
   png_free(png_voidcast(png_const_structrp,png_ptr), ptr);
}

void png_reset_crc

(

png_structrp

png_ptr

)

{
   /* The cast is safe because the crc is a 32 bit value. */
   png_ptr->crc = (png_uint_32)crc32(0, Z_NULL, 0);
}

void png_calculate_crc	(	png_structrp	png_ptr,
		png_const_bytep	ptr,
		png_size_t	length
	)

{
   int need_crc = 1;

   if (PNG_CHUNK_ANCILLARY(png_ptr->chunk_name) != 0)
   {
      if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_MASK) ==
          (PNG_FLAG_CRC_ANCILLARY_USE | PNG_FLAG_CRC_ANCILLARY_NOWARN))
         need_crc = 0;
   }

   else /* critical */
   {
      if ((png_ptr->flags & PNG_FLAG_CRC_CRITICAL_IGNORE) != 0)
         need_crc = 0;
   }

   /* 'uLong' is defined in zlib.h as unsigned long; this means that on some
    * systems it is a 64 bit value.  crc32, however, returns 32 bits so the
    * following cast is safe.  'uInt' may be no more than 16 bits, so it is
    * necessary to perform a loop here.
    */
   if (need_crc != 0 && length > 0)
   {
      uLong crc = png_ptr->crc; /* Should never issue a warning */

      do
      {
         uInt safe_length = (uInt)length;
         if (safe_length == 0)
            safe_length = (uInt)-1; /* evil, but safe */

         crc = crc32(crc, ptr, safe_length);

         /* The following should never issue compiler warnings; if they do the
          * target system has characteristics that will probably violate other
          * assumptions within the libpng code.
          */
         ptr += safe_length;
         length -= safe_length;
      }
      while (length > 0);

      /* And the following is always safe because the crc is only 32 bits. */
      png_ptr->crc = (png_uint_32)crc;
   }
}

int png_user_version_check	(	png_structrp	png_ptr,
		png_const_charp	user_png_ver
	)

{
     /* Libpng versions 1.0.0 and later are binary compatible if the version
      * string matches through the second '.'; we must recompile any
      * applications that use any older library version.
      */

   if (user_png_ver != NULL)
   {
      int i = -1;
      int found_dots = 0;

      do
      {
         i++;
         if (user_png_ver[i] != PNG_LIBPNG_VER_STRING[i])
            png_ptr->flags |= PNG_FLAG_LIBRARY_MISMATCH;
         if (user_png_ver[i] == '.')
            found_dots++;
      } while (found_dots < 2 && user_png_ver[i] != 0 &&
            PNG_LIBPNG_VER_STRING[i] != 0);
   }

   else
      png_ptr->flags |= PNG_FLAG_LIBRARY_MISMATCH;

   if ((png_ptr->flags & PNG_FLAG_LIBRARY_MISMATCH) != 0)
   {
#ifdef PNG_WARNINGS_SUPPORTED
      size_t pos = 0;
      char m[128];

      pos = png_safecat(m, (sizeof m), pos,
          "Application built with libpng-");
      pos = png_safecat(m, (sizeof m), pos, user_png_ver);
      pos = png_safecat(m, (sizeof m), pos, " but running with ");
      pos = png_safecat(m, (sizeof m), pos, PNG_LIBPNG_VER_STRING);
      PNG_UNUSED(pos)

      png_warning(png_ptr, m);
#endif

#ifdef PNG_ERROR_NUMBERS_SUPPORTED
      png_ptr->flags = 0;
#endif

      return 0;
   }

   /* Success return. */
   return 1;
}

png_structp png_create_png_struct	(	png_const_charp	user_png_ver,
		png_voidp	error_ptr,
		png_error_ptr	error_fn,
		png_error_ptr	warn_fn,
		png_voidp	mem_ptr,
		png_malloc_ptr	malloc_fn,
		png_free_ptr	free_fn
	)

{
   png_struct create_struct;
#  ifdef PNG_SETJMP_SUPPORTED
      jmp_buf create_jmp_buf;
#  endif

   /* This temporary stack-allocated structure is used to provide a place to
    * build enough context to allow the user provided memory allocator (if any)
    * to be called.
    */
   memset(&create_struct, 0, (sizeof create_struct));

   /* Added at libpng-1.2.6 */
#  ifdef PNG_USER_LIMITS_SUPPORTED
      create_struct.user_width_max = PNG_USER_WIDTH_MAX;
      create_struct.user_height_max = PNG_USER_HEIGHT_MAX;

#     ifdef PNG_USER_CHUNK_CACHE_MAX
         /* Added at libpng-1.2.43 and 1.4.0 */
         create_struct.user_chunk_cache_max = PNG_USER_CHUNK_CACHE_MAX;
#     endif

#     ifdef PNG_USER_CHUNK_MALLOC_MAX
         /* Added at libpng-1.2.43 and 1.4.1, required only for read but exists
          * in png_struct regardless.
          */
         create_struct.user_chunk_malloc_max = PNG_USER_CHUNK_MALLOC_MAX;
#     endif
#  endif

   /* The following two API calls simply set fields in png_struct, so it is safe
    * to do them now even though error handling is not yet set up.
    */
#  ifdef PNG_USER_MEM_SUPPORTED
      png_set_mem_fn(&create_struct, mem_ptr, malloc_fn, free_fn);
#  else
      PNG_UNUSED(mem_ptr)
      PNG_UNUSED(malloc_fn)
      PNG_UNUSED(free_fn)
#  endif

   /* (*error_fn) can return control to the caller after the error_ptr is set,
    * this will result in a memory leak unless the error_fn does something
    * extremely sophisticated.  The design lacks merit but is implicit in the
    * API.
    */
   png_set_error_fn(&create_struct, error_ptr, error_fn, warn_fn);

#  ifdef PNG_SETJMP_SUPPORTED
      if (!setjmp(create_jmp_buf))
      {
         /* Temporarily fake out the longjmp information until we have
          * successfully completed this function.  This only works if we have
          * setjmp() support compiled in, but it is safe - this stuff should
          * never happen.
          */
         create_struct.jmp_buf_ptr = &create_jmp_buf;
         create_struct.jmp_buf_size = 0; /*stack allocation*/
         create_struct.longjmp_fn = longjmp;
#  else
      {
#  endif
         /* Call the general version checker (shared with read and write code):
          */
         if (png_user_version_check(&create_struct, user_png_ver) != 0)
         {
            png_structrp png_ptr = png_voidcast(png_structrp,
               png_malloc_warn(&create_struct, (sizeof *png_ptr)));

            if (png_ptr != NULL)
            {
               /* png_ptr->zstream holds a back-pointer to the png_struct, so
                * this can only be done now:
                */
               create_struct.zstream.zalloc = png_zalloc;
               create_struct.zstream.zfree = png_zfree;
               create_struct.zstream.opaque = png_ptr;

#              ifdef PNG_SETJMP_SUPPORTED
                  /* Eliminate the local error handling: */
                  create_struct.jmp_buf_ptr = NULL;
                  create_struct.jmp_buf_size = 0;
                  create_struct.longjmp_fn = 0;
#              endif

               *png_ptr = create_struct;

               /* This is the successful return point */
               return png_ptr;
            }
         }
      }

   /* A longjmp because of a bug in the application storage allocator or a
    * simple failure to allocate the png_struct.
    */
   return NULL;
}

png_infop png_create_info_struct

(

png_const_structrp

png_ptr

)

{
   png_inforp info_ptr;

   png_debug(1, "in png_create_info_struct");

   if (png_ptr == NULL)
      return NULL;

   /* Use the internal API that does not (or at least should not) error out, so
    * that this call always returns ok.  The application typically sets up the
    * error handling *after* creating the info_struct because this is the way it
    * has always been done in 'example.c'.
    */
   info_ptr = png_voidcast(png_inforp, png_malloc_base(png_ptr,
      (sizeof *info_ptr)));

   if (info_ptr != NULL)
      memset(info_ptr, 0, (sizeof *info_ptr));

   return info_ptr;
}

void png_destroy_info_struct	(	png_const_structrp	png_ptr,
		png_infopp	info_ptr_ptr
	)

{
   png_inforp info_ptr = NULL;

   png_debug(1, "in png_destroy_info_struct");

   if (png_ptr == NULL)
      return;

   if (info_ptr_ptr != NULL)
      info_ptr = *info_ptr_ptr;

   if (info_ptr != NULL)
   {
      /* Do this first in case of an error below; if the app implements its own
       * memory management this can lead to png_free calling png_error, which
       * will abort this routine and return control to the app error handler.
       * An infinite loop may result if it then tries to free the same info
       * ptr.
       */
      *info_ptr_ptr = NULL;

      png_free_data(png_ptr, info_ptr, PNG_FREE_ALL, -1);
      memset(info_ptr, 0, (sizeof *info_ptr));
      png_free(png_ptr, info_ptr);
   }
}

void png_info_init_3	(	png_infopp	ptr_ptr,
		png_size_t	png_info_struct_size
	)

{
   png_inforp info_ptr = *ptr_ptr;

   png_debug(1, "in png_info_init_3");

   if (info_ptr == NULL)
      return;

   if ((sizeof (png_info)) > png_info_struct_size)
   {
      *ptr_ptr = NULL;
      /* The following line is why this API should not be used: */
      free(info_ptr);
      info_ptr = png_voidcast(png_inforp, png_malloc_base(NULL,
         (sizeof *info_ptr)));
      *ptr_ptr = info_ptr;
   }

   /* Set everything to 0 */
   memset(info_ptr, 0, (sizeof *info_ptr));
}

void png_data_freer	(	png_const_structrp	png_ptr,
		png_inforp	info_ptr,
		int	freer,
		png_uint_32	mask
	)

{
   png_debug(1, "in png_data_freer");

   if (png_ptr == NULL || info_ptr == NULL)
      return;

   if (freer == PNG_DESTROY_WILL_FREE_DATA)
      info_ptr->free_me |= mask;

   else if (freer == PNG_USER_WILL_FREE_DATA)
      info_ptr->free_me &= ~mask;

   else
      png_error(png_ptr, "Unknown freer parameter in png_data_freer");
}

void png_free_data	(	png_const_structrp	png_ptr,
		png_inforp	info_ptr,
		png_uint_32	mask,
		int	num
	)

{
   png_debug(1, "in png_free_data");

   if (png_ptr == NULL || info_ptr == NULL)
      return;

#ifdef PNG_TEXT_SUPPORTED
   /* Free text item num or (if num == -1) all text items */
   if (info_ptr->text != 0 &&
       ((mask & PNG_FREE_TEXT) & info_ptr->free_me) != 0)
   {
      if (num != -1)
      {
         png_free(png_ptr, info_ptr->text[num].key);
         info_ptr->text[num].key = NULL;
      }

      else
      {
         int i;

         for (i = 0; i < info_ptr->num_text; i++)
            png_free(png_ptr, info_ptr->text[i].key);

         png_free(png_ptr, info_ptr->text);
         info_ptr->text = NULL;
         info_ptr->num_text = 0;
      }
   }
#endif

#ifdef PNG_tRNS_SUPPORTED
   /* Free any tRNS entry */
   if (((mask & PNG_FREE_TRNS) & info_ptr->free_me) != 0)
   {
      png_free(png_ptr, info_ptr->trans_alpha);
      info_ptr->trans_alpha = NULL;
      info_ptr->valid &= ~PNG_INFO_tRNS;
   }
#endif

#ifdef PNG_sCAL_SUPPORTED
   /* Free any sCAL entry */
   if (((mask & PNG_FREE_SCAL) & info_ptr->free_me) != 0)
   {
      png_free(png_ptr, info_ptr->scal_s_width);
      png_free(png_ptr, info_ptr->scal_s_height);
      info_ptr->scal_s_width = NULL;
      info_ptr->scal_s_height = NULL;
      info_ptr->valid &= ~PNG_INFO_sCAL;
   }
#endif

#ifdef PNG_pCAL_SUPPORTED
   /* Free any pCAL entry */
   if (((mask & PNG_FREE_PCAL) & info_ptr->free_me) != 0)
   {
      png_free(png_ptr, info_ptr->pcal_purpose);
      png_free(png_ptr, info_ptr->pcal_units);
      info_ptr->pcal_purpose = NULL;
      info_ptr->pcal_units = NULL;

      if (info_ptr->pcal_params != NULL)
         {
            int i;

            for (i = 0; i < info_ptr->pcal_nparams; i++)
               png_free(png_ptr, info_ptr->pcal_params[i]);

            png_free(png_ptr, info_ptr->pcal_params);
            info_ptr->pcal_params = NULL;
         }
      info_ptr->valid &= ~PNG_INFO_pCAL;
   }
#endif

#ifdef PNG_iCCP_SUPPORTED
   /* Free any profile entry */
   if (((mask & PNG_FREE_ICCP) & info_ptr->free_me) != 0)
   {
      png_free(png_ptr, info_ptr->iccp_name);
      png_free(png_ptr, info_ptr->iccp_profile);
      info_ptr->iccp_name = NULL;
      info_ptr->iccp_profile = NULL;
      info_ptr->valid &= ~PNG_INFO_iCCP;
   }
#endif

#ifdef PNG_sPLT_SUPPORTED
   /* Free a given sPLT entry, or (if num == -1) all sPLT entries */
   if (info_ptr->splt_palettes != 0 &&
       ((mask & PNG_FREE_SPLT) & info_ptr->free_me) != 0)
   {
      if (num != -1)
      {
         png_free(png_ptr, info_ptr->splt_palettes[num].name);
         png_free(png_ptr, info_ptr->splt_palettes[num].entries);
         info_ptr->splt_palettes[num].name = NULL;
         info_ptr->splt_palettes[num].entries = NULL;
      }

      else
      {
         if (info_ptr->splt_palettes_num != 0)
         {
            int i;

            for (i = 0; i < info_ptr->splt_palettes_num; i++)
            {
               png_free(png_ptr, info_ptr->splt_palettes[i].name);
               png_free(png_ptr, info_ptr->splt_palettes[i].entries);
            }

            png_free(png_ptr, info_ptr->splt_palettes);
            info_ptr->splt_palettes = NULL;
            info_ptr->splt_palettes_num = 0;
         }
         info_ptr->valid &= ~PNG_INFO_sPLT;
      }
   }
#endif

#ifdef PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED
   if (info_ptr->unknown_chunks != 0 &&
       ((mask & PNG_FREE_UNKN) & info_ptr->free_me) != 0)
   {
      if (num != -1)
      {
          png_free(png_ptr, info_ptr->unknown_chunks[num].data);
          info_ptr->unknown_chunks[num].data = NULL;
      }

      else
      {
         int i;

         if (info_ptr->unknown_chunks_num != 0)
         {
            for (i = 0; i < info_ptr->unknown_chunks_num; i++)
               png_free(png_ptr, info_ptr->unknown_chunks[i].data);

            png_free(png_ptr, info_ptr->unknown_chunks);
            info_ptr->unknown_chunks = NULL;
            info_ptr->unknown_chunks_num = 0;
         }
      }
   }
#endif

#ifdef PNG_hIST_SUPPORTED
   /* Free any hIST entry */
   if (((mask & PNG_FREE_HIST) & info_ptr->free_me) != 0)
   {
      png_free(png_ptr, info_ptr->hist);
      info_ptr->hist = NULL;
      info_ptr->valid &= ~PNG_INFO_hIST;
   }
#endif

   /* Free any PLTE entry that was internally allocated */
   if (((mask & PNG_FREE_PLTE) & info_ptr->free_me) != 0)
   {
      png_free(png_ptr, info_ptr->palette);
      info_ptr->palette = NULL;
      info_ptr->valid &= ~PNG_INFO_PLTE;
      info_ptr->num_palette = 0;
   }

#ifdef PNG_INFO_IMAGE_SUPPORTED
   /* Free any image bits attached to the info structure */
   if (((mask & PNG_FREE_ROWS) & info_ptr->free_me) != 0)
   {
      if (info_ptr->row_pointers != 0)
      {
         png_uint_32 row;
         for (row = 0; row < info_ptr->height; row++)
            png_free(png_ptr, info_ptr->row_pointers[row]);

         png_free(png_ptr, info_ptr->row_pointers);
         info_ptr->row_pointers = NULL;
      }
      info_ptr->valid &= ~PNG_INFO_IDAT;
   }
#endif

   if (num != -1)
      mask &= ~PNG_FREE_MUL;

   info_ptr->free_me &= ~mask;
}

png_voidp png_get_io_ptr

(

png_const_structrp

png_ptr

)

{
   if (png_ptr == NULL)
      return (NULL);

   return (png_ptr->io_ptr);
}

void png_init_io	(	png_structrp	png_ptr,
		png_FILE_p	fp
	)

{
   png_debug(1, "in png_init_io");

   if (png_ptr == NULL)
      return;

   png_ptr->io_ptr = (png_voidp)fp;
}

void png_save_int_32	(	png_bytep	buf,
		png_int_32	i
	)

{
   buf[0] = (png_byte)((i >> 24) & 0xff);
   buf[1] = (png_byte)((i >> 16) & 0xff);
   buf[2] = (png_byte)((i >> 8) & 0xff);
   buf[3] = (png_byte)(i & 0xff);
}

int png_convert_to_rfc1123_buffer	(	char	out[29],
		png_const_timep	ptime
	)

{
   static PNG_CONST char short_months[12][4] =
        {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
         "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};

   if (out == NULL)
      return 0;

   if (ptime->year > 9999 /* RFC1123 limitation */ ||
       ptime->month == 0    ||  ptime->month > 12  ||
       ptime->day   == 0    ||  ptime->day   > 31  ||
       ptime->hour  > 23    ||  ptime->minute > 59 ||
       ptime->second > 60)
      return 0;

   {
      size_t pos = 0;
      char number_buf[5]; /* enough for a four-digit year */

#     define APPEND_STRING(string) pos = png_safecat(out, 29, pos, (string))
#     define APPEND_NUMBER(format, value)\
         APPEND_STRING(PNG_FORMAT_NUMBER(number_buf, format, (value)))
#     define APPEND(ch) if (pos < 28) out[pos++] = (ch)

      APPEND_NUMBER(PNG_NUMBER_FORMAT_u, (unsigned)ptime->day);
      APPEND(' ');
      APPEND_STRING(short_months[(ptime->month - 1)]);
      APPEND(' ');
      APPEND_NUMBER(PNG_NUMBER_FORMAT_u, ptime->year);
      APPEND(' ');
      APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->hour);
      APPEND(':');
      APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->minute);
      APPEND(':');
      APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->second);
      APPEND_STRING(" +0000"); /* This reliably terminates the buffer */

#     undef APPEND
#     undef APPEND_NUMBER
#     undef APPEND_STRING
   }

   return 1;
}

png_const_charp png_convert_to_rfc1123	(	png_structrp	png_ptr,
		png_const_timep	ptime
	)

{
   if (png_ptr != NULL)
   {
      /* The only failure above if png_ptr != NULL is from an invalid ptime */
      if (png_convert_to_rfc1123_buffer(png_ptr->time_buffer, ptime) == 0)
         png_warning(png_ptr, "Ignoring invalid time value");

      else
         return png_ptr->time_buffer;
   }

   return NULL;
}

png_const_charp png_get_copyright

(

png_const_structrp

png_ptr

)

{
   PNG_UNUSED(png_ptr)  /* Silence compiler warning about unused png_ptr */
#ifdef PNG_STRING_COPYRIGHT
   return PNG_STRING_COPYRIGHT
#else
#  ifdef __STDC__
   return PNG_STRING_NEWLINE \
     "libpng version 1.6.16 - December 22, 2014" PNG_STRING_NEWLINE \
     "Copyright (c) 1998-2014 Glenn Randers-Pehrson" PNG_STRING_NEWLINE \
     "Copyright (c) 1996-1997 Andreas Dilger" PNG_STRING_NEWLINE \
     "Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc." \
     PNG_STRING_NEWLINE;
#  else
      return "libpng version 1.6.16 - December 22, 2014\
      Copyright (c) 1998-2014 Glenn Randers-Pehrson\
      Copyright (c) 1996-1997 Andreas Dilger\
      Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";
#  endif
#endif
}

png_const_charp png_get_libpng_ver

(

png_const_structrp

png_ptr

)

{
   /* Version of *.c files used when building libpng */
   return png_get_header_ver(png_ptr);
}

png_const_charp png_get_header_ver

(

png_const_structrp

png_ptr

)

{
   /* Version of *.h files used when building libpng */
   PNG_UNUSED(png_ptr)  /* Silence compiler warning about unused png_ptr */
   return PNG_LIBPNG_VER_STRING;
}

png_const_charp png_get_header_version

(

png_const_structrp

png_ptr

)

{
   /* Returns longer string containing both version and date */
   PNG_UNUSED(png_ptr)  /* Silence compiler warning about unused png_ptr */
#ifdef __STDC__
   return PNG_HEADER_VERSION_STRING
#  ifndef PNG_READ_SUPPORTED
   "     (NO READ SUPPORT)"
#  endif
   PNG_STRING_NEWLINE;
#else
   return PNG_HEADER_VERSION_STRING;
#endif
}

void png_build_grayscale_palette	(	int	bit_depth,
		png_colorp	palette
	)

{
   int num_palette;
   int color_inc;
   int i;
   int v;

   png_debug(1, "in png_do_build_grayscale_palette");

   if (palette == NULL)
      return;

   switch (bit_depth)
   {
      case 1:
         num_palette = 2;
         color_inc = 0xff;
         break;

      case 2:
         num_palette = 4;
         color_inc = 0x55;
         break;

      case 4:
         num_palette = 16;
         color_inc = 0x11;
         break;

      case 8:
         num_palette = 256;
         color_inc = 1;
         break;

      default:
         num_palette = 0;
         color_inc = 0;
         break;
   }

   for (i = 0, v = 0; i < num_palette; i++, v += color_inc)
   {
      palette[i].red = (png_byte)v;
      palette[i].green = (png_byte)v;
      palette[i].blue = (png_byte)v;
   }
}

int png_handle_as_unknown	(	png_const_structrp	png_ptr,
		png_const_bytep	chunk_name
	)

{
   /* Check chunk_name and return "keep" value if it's on the list, else 0 */
   png_const_bytep p, p_end;

   if (png_ptr == NULL || chunk_name == NULL || png_ptr->num_chunk_list == 0)
      return PNG_HANDLE_CHUNK_AS_DEFAULT;

   p_end = png_ptr->chunk_list;
   p = p_end + png_ptr->num_chunk_list*5; /* beyond end */

   /* The code is the fifth byte after each four byte string.  Historically this
    * code was always searched from the end of the list, this is no longer
    * necessary because the 'set' routine handles duplicate entries correcty.
    */
   do /* num_chunk_list > 0, so at least one */
   {
      p -= 5;

      if (memcmp(chunk_name, p, 4) == 0)
         return p[4];
   }
   while (p > p_end);

   /* This means that known chunks should be processed and unknown chunks should
    * be handled according to the value of png_ptr->unknown_default; this can be
    * confusing because, as a result, there are two levels of defaulting for
    * unknown chunks.
    */
   return PNG_HANDLE_CHUNK_AS_DEFAULT;
}

int png_chunk_unknown_handling	(	png_const_structrp	png_ptr,
		png_uint_32	chunk_name
	)

{
   png_byte chunk_string[5];

   PNG_CSTRING_FROM_CHUNK(chunk_string, chunk_name);
   return png_handle_as_unknown(png_ptr, chunk_string);
}

int png_reset_zstream

(

png_structrp

png_ptr

)

{
   if (png_ptr == NULL)
      return Z_STREAM_ERROR;

   /* WARNING: this resets the window bits to the maximum! */
   return (inflateReset(&png_ptr->zstream));
}

png_uint_32 png_access_version_number

(

void

)

{
   /* Version of *.c files used when building libpng */
   return((png_uint_32)PNG_LIBPNG_VER);
}

void png_zstream_error	(	png_structrp	png_ptr,
		int	ret
	)

{
   /* Translate 'ret' into an appropriate error string, priority is given to the
    * one in zstream if set.  This always returns a string, even in cases like
    * Z_OK or Z_STREAM_END where the error code is a success code.
    */
   if (png_ptr->zstream.msg == NULL) switch (ret)
   {
      default:
      case Z_OK:
         png_ptr->zstream.msg = PNGZ_MSG_CAST("unexpected zlib return code");
         break;

      case Z_STREAM_END:
         /* Normal exit */
         png_ptr->zstream.msg = PNGZ_MSG_CAST("unexpected end of LZ stream");
         break;

      case Z_NEED_DICT:
         /* This means the deflate stream did not have a dictionary; this
          * indicates a bogus PNG.
          */
         png_ptr->zstream.msg = PNGZ_MSG_CAST("missing LZ dictionary");
         break;

      case Z_ERRNO:
         /* gz APIs only: should not happen */
         png_ptr->zstream.msg = PNGZ_MSG_CAST("zlib IO error");
         break;

      case Z_STREAM_ERROR:
         /* internal libpng error */
         png_ptr->zstream.msg = PNGZ_MSG_CAST("bad parameters to zlib");
         break;

      case Z_DATA_ERROR:
         png_ptr->zstream.msg = PNGZ_MSG_CAST("damaged LZ stream");
         break;

      case Z_MEM_ERROR:
         png_ptr->zstream.msg = PNGZ_MSG_CAST("insufficient memory");
         break;

      case Z_BUF_ERROR:
         /* End of input or output; not a problem if the caller is doing
          * incremental read or write.
          */
         png_ptr->zstream.msg = PNGZ_MSG_CAST("truncated");
         break;

      case Z_VERSION_ERROR:
         png_ptr->zstream.msg = PNGZ_MSG_CAST("unsupported zlib version");
         break;

      case PNG_UNEXPECTED_ZLIB_RETURN:
         /* Compile errors here mean that zlib now uses the value co-opted in
          * pngpriv.h for PNG_UNEXPECTED_ZLIB_RETURN; update the switch above
          * and change pngpriv.h.  Note that this message is "... return",
          * whereas the default/Z_OK one is "... return code".
          */
         png_ptr->zstream.msg = PNGZ_MSG_CAST("unexpected zlib return");
         break;
   }
}

static int png_colorspace_check_gamma ( png_const_structrp  png_ptr, png_colorspacerp  colorspace, png_fixed_point  gAMA, int  from  )

static

{
   png_fixed_point gtest;

   if ((colorspace->flags & PNG_COLORSPACE_HAVE_GAMMA) != 0 &&
      (png_muldiv(&gtest, colorspace->gamma, PNG_FP_1, gAMA) == 0  ||
      png_gamma_significant(gtest) != 0))
   {
      /* Either this is an sRGB image, in which case the calculated gamma
       * approximation should match, or this is an image with a profile and the
       * value libpng calculates for the gamma of the profile does not match the
       * value recorded in the file.  The former, sRGB, case is an error, the
       * latter is just a warning.
       */
      if ((colorspace->flags & PNG_COLORSPACE_FROM_sRGB) != 0 || from == 2)
      {
         png_chunk_report(png_ptr, "gamma value does not match sRGB",
            PNG_CHUNK_ERROR);
         /* Do not overwrite an sRGB value */
         return from == 2;
      }

      else /* sRGB tag not involved */
      {
         png_chunk_report(png_ptr, "gamma value does not match libpng estimate",
            PNG_CHUNK_WARNING);
         return from == 1;
      }
   }

   return 1;
}

void png_colorspace_set_gamma	(	png_const_structrp	png_ptr,
		png_colorspacerp	colorspace,
		png_fixed_point	gAMA
	)

{
   /* Changed in libpng-1.5.4 to limit the values to ensure overflow can't
    * occur.  Since the fixed point representation is asymetrical it is
    * possible for 1/gamma to overflow the limit of 21474 and this means the
    * gamma value must be at least 5/100000 and hence at most 20000.0.  For
    * safety the limits here are a little narrower.  The values are 0.00016 to
    * 6250.0, which are truly ridiculous gamma values (and will produce
    * displays that are all black or all white.)
    *
    * In 1.6.0 this test replaces the ones in pngrutil.c, in the gAMA chunk
    * handling code, which only required the value to be >0.
    */
   png_const_charp errmsg;

   if (gAMA < 16 || gAMA > 625000000)
      errmsg = "gamma value out of range";

#  ifdef PNG_READ_gAMA_SUPPORTED
      /* Allow the application to set the gamma value more than once */
      else if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0 &&
         (colorspace->flags & PNG_COLORSPACE_FROM_gAMA) != 0)
         errmsg = "duplicate";
#  endif

   /* Do nothing if the colorspace is already invalid */
   else if ((colorspace->flags & PNG_COLORSPACE_INVALID) != 0)
      return;

   else
   {
      if (png_colorspace_check_gamma(png_ptr, colorspace, gAMA,
          1/*from gAMA*/) != 0)
      {
         /* Store this gamma value. */
         colorspace->gamma = gAMA;
         colorspace->flags |=
            (PNG_COLORSPACE_HAVE_GAMMA | PNG_COLORSPACE_FROM_gAMA);
      }

      /* At present if the check_gamma test fails the gamma of the colorspace is
       * not updated however the colorspace is not invalidated.  This
       * corresponds to the case where the existing gamma comes from an sRGB
       * chunk or profile.  An error message has already been output.
       */
      return;
   }

   /* Error exit - errmsg has been set. */
   colorspace->flags |= PNG_COLORSPACE_INVALID;
   png_chunk_report(png_ptr, errmsg, PNG_CHUNK_WRITE_ERROR);
}

void png_colorspace_sync_info	(	png_const_structrp	png_ptr,
		png_inforp	info_ptr
	)

{
   if ((info_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) != 0)
   {
      /* Everything is invalid */
      info_ptr->valid &= ~(PNG_INFO_gAMA|PNG_INFO_cHRM|PNG_INFO_sRGB|
         PNG_INFO_iCCP);

#     ifdef PNG_COLORSPACE_SUPPORTED
         /* Clean up the iCCP profile now if it won't be used. */
         png_free_data(png_ptr, info_ptr, PNG_FREE_ICCP, -1/*not used*/);
#     else
         PNG_UNUSED(png_ptr)
#     endif
   }

   else
   {
#     ifdef PNG_COLORSPACE_SUPPORTED
         /* Leave the INFO_iCCP flag set if the pngset.c code has already set
          * it; this allows a PNG to contain a profile which matches sRGB and
          * yet still have that profile retrievable by the application.
          */
         if ((info_ptr->colorspace.flags & PNG_COLORSPACE_MATCHES_sRGB) != 0)
            info_ptr->valid |= PNG_INFO_sRGB;

         else
            info_ptr->valid &= ~PNG_INFO_sRGB;

         if ((info_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_ENDPOINTS) != 0)
            info_ptr->valid |= PNG_INFO_cHRM;

         else
            info_ptr->valid &= ~PNG_INFO_cHRM;
#     endif

      if ((info_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_GAMMA) != 0)
         info_ptr->valid |= PNG_INFO_gAMA;

      else
         info_ptr->valid &= ~PNG_INFO_gAMA;
   }
}

void png_colorspace_sync	(	png_const_structrp	png_ptr,
		png_inforp	info_ptr
	)

{
   if (info_ptr == NULL) /* reduce code size; check here not in the caller */
      return;

   info_ptr->colorspace = png_ptr->colorspace;
   png_colorspace_sync_info(png_ptr, info_ptr);
}

static int png_xy_from_XYZ ( png_xy *  xy, const png_XYZ *  XYZ  )

static

{
   png_int_32 d, dwhite, whiteX, whiteY;

   d = XYZ->red_X + XYZ->red_Y + XYZ->red_Z;
   if (png_muldiv(&xy->redx, XYZ->red_X, PNG_FP_1, d) == 0)
      return 1;
   if (png_muldiv(&xy->redy, XYZ->red_Y, PNG_FP_1, d) == 0)
      return 1;
   dwhite = d;
   whiteX = XYZ->red_X;
   whiteY = XYZ->red_Y;

   d = XYZ->green_X + XYZ->green_Y + XYZ->green_Z;
   if (png_muldiv(&xy->greenx, XYZ->green_X, PNG_FP_1, d) == 0)
      return 1;
   if (png_muldiv(&xy->greeny, XYZ->green_Y, PNG_FP_1, d) == 0)
      return 1;
   dwhite += d;
   whiteX += XYZ->green_X;
   whiteY += XYZ->green_Y;

   d = XYZ->blue_X + XYZ->blue_Y + XYZ->blue_Z;
   if (png_muldiv(&xy->bluex, XYZ->blue_X, PNG_FP_1, d) == 0)
      return 1;
   if (png_muldiv(&xy->bluey, XYZ->blue_Y, PNG_FP_1, d) == 0)
      return 1;
   dwhite += d;
   whiteX += XYZ->blue_X;
   whiteY += XYZ->blue_Y;

   /* The reference white is simply the sum of the end-point (X,Y,Z) vectors,
    * thus:
    */
   if (png_muldiv(&xy->whitex, whiteX, PNG_FP_1, dwhite) == 0)
      return 1;
   if (png_muldiv(&xy->whitey, whiteY, PNG_FP_1, dwhite) == 0)
      return 1;

   return 0;
}

static int png_XYZ_from_xy ( png_XYZ *  XYZ, const png_xy *  xy  )

static

{
   png_fixed_point red_inverse, green_inverse, blue_scale;
   png_fixed_point left, right, denominator;

   /* Check xy and, implicitly, z.  Note that wide gamut color spaces typically
    * have end points with 0 tristimulus values (these are impossible end
    * points, but they are used to cover the possible colors.)
    */
   if (xy->redx < 0 || xy->redx > PNG_FP_1) return 1;
   if (xy->redy < 0 || xy->redy > PNG_FP_1-xy->redx) return 1;
   if (xy->greenx < 0 || xy->greenx > PNG_FP_1) return 1;
   if (xy->greeny < 0 || xy->greeny > PNG_FP_1-xy->greenx) return 1;
   if (xy->bluex < 0 || xy->bluex > PNG_FP_1) return 1;
   if (xy->bluey < 0 || xy->bluey > PNG_FP_1-xy->bluex) return 1;
   if (xy->whitex < 0 || xy->whitex > PNG_FP_1) return 1;
   if (xy->whitey < 0 || xy->whitey > PNG_FP_1-xy->whitex) return 1;

   /* The reverse calculation is more difficult because the original tristimulus
    * value had 9 independent values (red,green,blue)x(X,Y,Z) however only 8
    * derived values were recorded in the cHRM chunk;
    * (red,green,blue,white)x(x,y).  This loses one degree of freedom and
    * therefore an arbitrary ninth value has to be introduced to undo the
    * original transformations.
    *
    * Think of the original end-points as points in (X,Y,Z) space.  The
    * chromaticity values (c) have the property:
    *
    *           C
    *   c = ---------
    *       X + Y + Z
    *
    * For each c (x,y,z) from the corresponding original C (X,Y,Z).  Thus the
    * three chromaticity values (x,y,z) for each end-point obey the
    * relationship:
    *
    *   x + y + z = 1
    *
    * This describes the plane in (X,Y,Z) space that intersects each axis at the
    * value 1.0; call this the chromaticity plane.  Thus the chromaticity
    * calculation has scaled each end-point so that it is on the x+y+z=1 plane
    * and chromaticity is the intersection of the vector from the origin to the
    * (X,Y,Z) value with the chromaticity plane.
    *
    * To fully invert the chromaticity calculation we would need the three
    * end-point scale factors, (red-scale, green-scale, blue-scale), but these
    * were not recorded.  Instead we calculated the reference white (X,Y,Z) and
    * recorded the chromaticity of this.  The reference white (X,Y,Z) would have
    * given all three of the scale factors since:
    *
    *    color-C = color-c * color-scale
    *    white-C = red-C + green-C + blue-C
    *            = red-c*red-scale + green-c*green-scale + blue-c*blue-scale
    *
    * But cHRM records only white-x and white-y, so we have lost the white scale
    * factor:
    *
    *    white-C = white-c*white-scale
    *
    * To handle this the inverse transformation makes an arbitrary assumption
    * about white-scale:
    *
    *    Assume: white-Y = 1.0
    *    Hence:  white-scale = 1/white-y
    *    Or:     red-Y + green-Y + blue-Y = 1.0
    *
    * Notice the last statement of the assumption gives an equation in three of
    * the nine values we want to calculate.  8 more equations come from the
    * above routine as summarised at the top above (the chromaticity
    * calculation):
    *
    *    Given: color-x = color-X / (color-X + color-Y + color-Z)
    *    Hence: (color-x - 1)*color-X + color.x*color-Y + color.x*color-Z = 0
    *
    * This is 9 simultaneous equations in the 9 variables "color-C" and can be
    * solved by Cramer's rule.  Cramer's rule requires calculating 10 9x9 matrix
    * determinants, however this is not as bad as it seems because only 28 of
    * the total of 90 terms in the various matrices are non-zero.  Nevertheless
    * Cramer's rule is notoriously numerically unstable because the determinant
    * calculation involves the difference of large, but similar, numbers.  It is
    * difficult to be sure that the calculation is stable for real world values
    * and it is certain that it becomes unstable where the end points are close
    * together.
    *
    * So this code uses the perhaps slightly less optimal but more
    * understandable and totally obvious approach of calculating color-scale.
    *
    * This algorithm depends on the precision in white-scale and that is
    * (1/white-y), so we can immediately see that as white-y approaches 0 the
    * accuracy inherent in the cHRM chunk drops off substantially.
    *
    * libpng arithmetic: a simple inversion of the above equations
    * ------------------------------------------------------------
    *
    *    white_scale = 1/white-y
    *    white-X = white-x * white-scale
    *    white-Y = 1.0
    *    white-Z = (1 - white-x - white-y) * white_scale
    *
    *    white-C = red-C + green-C + blue-C
    *            = red-c*red-scale + green-c*green-scale + blue-c*blue-scale
    *
    * This gives us three equations in (red-scale,green-scale,blue-scale) where
    * all the coefficients are now known:
    *
    *    red-x*red-scale + green-x*green-scale + blue-x*blue-scale
    *       = white-x/white-y
    *    red-y*red-scale + green-y*green-scale + blue-y*blue-scale = 1
    *    red-z*red-scale + green-z*green-scale + blue-z*blue-scale
    *       = (1 - white-x - white-y)/white-y
    *
    * In the last equation color-z is (1 - color-x - color-y) so we can add all
    * three equations together to get an alternative third:
    *
    *    red-scale + green-scale + blue-scale = 1/white-y = white-scale
    *
    * So now we have a Cramer's rule solution where the determinants are just
    * 3x3 - far more tractible.  Unfortunately 3x3 determinants still involve
    * multiplication of three coefficients so we can't guarantee to avoid
    * overflow in the libpng fixed point representation.  Using Cramer's rule in
    * floating point is probably a good choice here, but it's not an option for
    * fixed point.  Instead proceed to simplify the first two equations by
    * eliminating what is likely to be the largest value, blue-scale:
    *
    *    blue-scale = white-scale - red-scale - green-scale
    *
    * Hence:
    *
    *    (red-x - blue-x)*red-scale + (green-x - blue-x)*green-scale =
    *                (white-x - blue-x)*white-scale
    *
    *    (red-y - blue-y)*red-scale + (green-y - blue-y)*green-scale =
    *                1 - blue-y*white-scale
    *
    * And now we can trivially solve for (red-scale,green-scale):
    *
    *    green-scale =
    *                (white-x - blue-x)*white-scale - (red-x - blue-x)*red-scale
    *                -----------------------------------------------------------
    *                                  green-x - blue-x
    *
    *    red-scale =
    *                1 - blue-y*white-scale - (green-y - blue-y) * green-scale
    *                ---------------------------------------------------------
    *                                  red-y - blue-y
    *
    * Hence:
    *
    *    red-scale =
    *          ( (green-x - blue-x) * (white-y - blue-y) -
    *            (green-y - blue-y) * (white-x - blue-x) ) / white-y
    * -------------------------------------------------------------------------
    *  (green-x - blue-x)*(red-y - blue-y)-(green-y - blue-y)*(red-x - blue-x)
    *
    *    green-scale =
    *          ( (red-y - blue-y) * (white-x - blue-x) -
    *            (red-x - blue-x) * (white-y - blue-y) ) / white-y
    * -------------------------------------------------------------------------
    *  (green-x - blue-x)*(red-y - blue-y)-(green-y - blue-y)*(red-x - blue-x)
    *
    * Accuracy:
    * The input values have 5 decimal digits of accuracy.  The values are all in
    * the range 0 < value < 1, so simple products are in the same range but may
    * need up to 10 decimal digits to preserve the original precision and avoid
    * underflow.  Because we are using a 32-bit signed representation we cannot
    * match this; the best is a little over 9 decimal digits, less than 10.
    *
    * The approach used here is to preserve the maximum precision within the
    * signed representation.  Because the red-scale calculation above uses the
    * difference between two products of values that must be in the range -1..+1
    * it is sufficient to divide the product by 7; ceil(100,000/32767*2).  The
    * factor is irrelevant in the calculation because it is applied to both
    * numerator and denominator.
    *
    * Note that the values of the differences of the products of the
    * chromaticities in the above equations tend to be small, for example for
    * the sRGB chromaticities they are:
    *
    * red numerator:    -0.04751
    * green numerator:  -0.08788
    * denominator:      -0.2241 (without white-y multiplication)
    *
    *  The resultant Y coefficients from the chromaticities of some widely used
    *  color space definitions are (to 15 decimal places):
    *
    *  sRGB
    *    0.212639005871510 0.715168678767756 0.072192315360734
    *  Kodak ProPhoto
    *    0.288071128229293 0.711843217810102 0.000085653960605
    *  Adobe RGB
    *    0.297344975250536 0.627363566255466 0.075291458493998
    *  Adobe Wide Gamut RGB
    *    0.258728243040113 0.724682314948566 0.016589442011321
    */
   /* By the argument, above overflow should be impossible here. The return
    * value of 2 indicates an internal error to the caller.
    */
   if (png_muldiv(&left, xy->greenx-xy->bluex, xy->redy - xy->bluey, 7) == 0)
      return 2;
   if (png_muldiv(&right, xy->greeny-xy->bluey, xy->redx - xy->bluex, 7) == 0)
      return 2;
   denominator = left - right;

   /* Now find the red numerator. */
   if (png_muldiv(&left, xy->greenx-xy->bluex, xy->whitey-xy->bluey, 7) == 0)
      return 2;
   if (png_muldiv(&right, xy->greeny-xy->bluey, xy->whitex-xy->bluex, 7) == 0)
      return 2;

   /* Overflow is possible here and it indicates an extreme set of PNG cHRM
    * chunk values.  This calculation actually returns the reciprocal of the
    * scale value because this allows us to delay the multiplication of white-y
    * into the denominator, which tends to produce a small number.
    */
   if (png_muldiv(&red_inverse, xy->whitey, denominator, left-right) == 0 ||
       red_inverse <= xy->whitey /* r+g+b scales = white scale */)
      return 1;

   /* Similarly for green_inverse: */
   if (png_muldiv(&left, xy->redy-xy->bluey, xy->whitex-xy->bluex, 7) == 0)
      return 2;
   if (png_muldiv(&right, xy->redx-xy->bluex, xy->whitey-xy->bluey, 7) == 0)
      return 2;
   if (png_muldiv(&green_inverse, xy->whitey, denominator, left-right) == 0 ||
       green_inverse <= xy->whitey)
      return 1;

   /* And the blue scale, the checks above guarantee this can't overflow but it
    * can still produce 0 for extreme cHRM values.
    */
   blue_scale = png_reciprocal(xy->whitey) - png_reciprocal(red_inverse) -
       png_reciprocal(green_inverse);
   if (blue_scale <= 0)
      return 1;


   /* And fill in the png_XYZ: */
   if (png_muldiv(&XYZ->red_X, xy->redx, PNG_FP_1, red_inverse) == 0)
      return 1;
   if (png_muldiv(&XYZ->red_Y, xy->redy, PNG_FP_1, red_inverse) == 0)
      return 1;
   if (png_muldiv(&XYZ->red_Z, PNG_FP_1 - xy->redx - xy->redy, PNG_FP_1,
       red_inverse) == 0)
      return 1;

   if (png_muldiv(&XYZ->green_X, xy->greenx, PNG_FP_1, green_inverse) == 0)
      return 1;
   if (png_muldiv(&XYZ->green_Y, xy->greeny, PNG_FP_1, green_inverse) == 0)
      return 1;
   if (png_muldiv(&XYZ->green_Z, PNG_FP_1 - xy->greenx - xy->greeny, PNG_FP_1,
       green_inverse) == 0)
      return 1;

   if (png_muldiv(&XYZ->blue_X, xy->bluex, blue_scale, PNG_FP_1) == 0)
      return 1;
   if (png_muldiv(&XYZ->blue_Y, xy->bluey, blue_scale, PNG_FP_1) == 0)
      return 1;
   if (png_muldiv(&XYZ->blue_Z, PNG_FP_1 - xy->bluex - xy->bluey, blue_scale,
       PNG_FP_1) == 0)
      return 1;

   return 0; /*success*/
}

static int png_XYZ_normalize ( png_XYZ *  XYZ )

static

{
   png_int_32 Y;

   if (XYZ->red_Y < 0 || XYZ->green_Y < 0 || XYZ->blue_Y < 0 ||
      XYZ->red_X < 0 || XYZ->green_X < 0 || XYZ->blue_X < 0 ||
      XYZ->red_Z < 0 || XYZ->green_Z < 0 || XYZ->blue_Z < 0)
      return 1;

   /* Normalize by scaling so the sum of the end-point Y values is PNG_FP_1.
    * IMPLEMENTATION NOTE: ANSI requires signed overflow not to occur, therefore
    * relying on addition of two positive values producing a negative one is not
    * safe.
    */
   Y = XYZ->red_Y;
   if (0x7fffffff - Y < XYZ->green_X)
      return 1;
   Y += XYZ->green_Y;
   if (0x7fffffff - Y < XYZ->blue_X)
      return 1;
   Y += XYZ->blue_Y;

   if (Y != PNG_FP_1)
   {
      if (png_muldiv(&XYZ->red_X, XYZ->red_X, PNG_FP_1, Y) == 0)
         return 1;
      if (png_muldiv(&XYZ->red_Y, XYZ->red_Y, PNG_FP_1, Y) == 0)
         return 1;
      if (png_muldiv(&XYZ->red_Z, XYZ->red_Z, PNG_FP_1, Y) == 0)
         return 1;

      if (png_muldiv(&XYZ->green_X, XYZ->green_X, PNG_FP_1, Y) == 0)
         return 1;
      if (png_muldiv(&XYZ->green_Y, XYZ->green_Y, PNG_FP_1, Y) == 0)
         return 1;
      if (png_muldiv(&XYZ->green_Z, XYZ->green_Z, PNG_FP_1, Y) == 0)
         return 1;

      if (png_muldiv(&XYZ->blue_X, XYZ->blue_X, PNG_FP_1, Y) == 0)
         return 1;
      if (png_muldiv(&XYZ->blue_Y, XYZ->blue_Y, PNG_FP_1, Y) == 0)
         return 1;
      if (png_muldiv(&XYZ->blue_Z, XYZ->blue_Z, PNG_FP_1, Y) == 0)
         return 1;
   }

   return 0;
}

static int png_colorspace_endpoints_match ( const png_xy *  xy1, const png_xy *  xy2, int  delta  )

static

{
   /* Allow an error of +/-0.01 (absolute value) on each chromaticity */
   if (PNG_OUT_OF_RANGE(xy1->whitex, xy2->whitex,delta) ||
       PNG_OUT_OF_RANGE(xy1->whitey, xy2->whitey,delta) ||
       PNG_OUT_OF_RANGE(xy1->redx,   xy2->redx,  delta) ||
       PNG_OUT_OF_RANGE(xy1->redy,   xy2->redy,  delta) ||
       PNG_OUT_OF_RANGE(xy1->greenx, xy2->greenx,delta) ||
       PNG_OUT_OF_RANGE(xy1->greeny, xy2->greeny,delta) ||
       PNG_OUT_OF_RANGE(xy1->bluex,  xy2->bluex, delta) ||
       PNG_OUT_OF_RANGE(xy1->bluey,  xy2->bluey, delta))
      return 0;
   return 1;
}

static int png_colorspace_check_xy ( png_XYZ *  XYZ, const png_xy *  xy  )

static

{
   int result;
   png_xy xy_test;

   /* As a side-effect this routine also returns the XYZ endpoints. */
   result = png_XYZ_from_xy(XYZ, xy);
   if (result != 0)
      return result;

   result = png_xy_from_XYZ(&xy_test, XYZ);
   if (result != 0)
      return result;

   if (png_colorspace_endpoints_match(xy, &xy_test,
       5/*actually, the math is pretty accurate*/) != 0)
      return 0;

   /* Too much slip */
   return 1;
}

static int png_colorspace_check_XYZ ( png_xy *  xy, png_XYZ *  XYZ  )

static

{
   int result;
   png_XYZ XYZtemp;

   result = png_XYZ_normalize(XYZ);
   if (result != 0)
      return result;

   result = png_xy_from_XYZ(xy, XYZ);
   if (result != 0)
      return result;

   XYZtemp = *XYZ;
   return png_colorspace_check_xy(&XYZtemp, xy);
}

static int png_colorspace_set_xy_and_XYZ ( png_const_structrp  png_ptr, png_colorspacerp  colorspace, const png_xy *  xy, const png_XYZ *  XYZ, int  preferred  )

static

{
   if ((colorspace->flags & PNG_COLORSPACE_INVALID) != 0)
      return 0;

   /* The consistency check is performed on the chromaticities; this factors out
    * variations because of the normalization (or not) of the end point Y
    * values.
    */
   if (preferred < 2 &&
       (colorspace->flags & PNG_COLORSPACE_HAVE_ENDPOINTS) != 0)
   {
      /* The end points must be reasonably close to any we already have.  The
       * following allows an error of up to +/-.001
       */
      if (png_colorspace_endpoints_match(xy, &colorspace->end_points_xy,
          100) == 0)
      {
         colorspace->flags |= PNG_COLORSPACE_INVALID;
         png_benign_error(png_ptr, "inconsistent chromaticities");
         return 0; /* failed */
      }

      /* Only overwrite with preferred values */
      if (preferred == 0)
         return 1; /* ok, but no change */
   }

   colorspace->end_points_xy = *xy;
   colorspace->end_points_XYZ = *XYZ;
   colorspace->flags |= PNG_COLORSPACE_HAVE_ENDPOINTS;

   /* The end points are normally quoted to two decimal digits, so allow +/-0.01
    * on this test.
    */
   if (png_colorspace_endpoints_match(xy, &sRGB_xy, 1000) != 0)
      colorspace->flags |= PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB;

   else
      colorspace->flags &= PNG_COLORSPACE_CANCEL(
         PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB);

   return 2; /* ok and changed */
}

int png_colorspace_set_chromaticities	(	png_const_structrp	png_ptr,
		png_colorspacerp	colorspace,
		const png_xy *	xy,
		int	preferred
	)

{
   /* We must check the end points to ensure they are reasonable - in the past
    * color management systems have crashed as a result of getting bogus
    * colorant values, while this isn't the fault of libpng it is the
    * responsibility of libpng because PNG carries the bomb and libpng is in a
    * position to protect against it.
    */
   png_XYZ XYZ;

   switch (png_colorspace_check_xy(&XYZ, xy))
   {
      case 0: /* success */
         return png_colorspace_set_xy_and_XYZ(png_ptr, colorspace, xy, &XYZ,
            preferred);

      case 1:
         /* We can't invert the chromaticities so we can't produce value XYZ
          * values.  Likely as not a color management system will fail too.
          */
         colorspace->flags |= PNG_COLORSPACE_INVALID;
         png_benign_error(png_ptr, "invalid chromaticities");
         break;

      default:
         /* libpng is broken; this should be a warning but if it happens we
          * want error reports so for the moment it is an error.
          */
         colorspace->flags |= PNG_COLORSPACE_INVALID;
         png_error(png_ptr, "internal error checking chromaticities");
         break;
   }

   return 0; /* failed */
}

int png_colorspace_set_endpoints	(	png_const_structrp	png_ptr,
		png_colorspacerp	colorspace,
		const png_XYZ *	XYZ_in,
		int	preferred
	)

{
   png_XYZ XYZ = *XYZ_in;
   png_xy xy;

   switch (png_colorspace_check_XYZ(&xy, &XYZ))
   {
      case 0:
         return png_colorspace_set_xy_and_XYZ(png_ptr, colorspace, &xy, &XYZ,
            preferred);

      case 1:
         /* End points are invalid. */
         colorspace->flags |= PNG_COLORSPACE_INVALID;
         png_benign_error(png_ptr, "invalid end points");
         break;

      default:
         colorspace->flags |= PNG_COLORSPACE_INVALID;
         png_error(png_ptr, "internal error checking chromaticities");
         break;
   }

   return 0; /* failed */
}

static char png_icc_tag_char ( png_uint_32  byte )

static

{
   byte &= 0xff;
   if (byte >= 32 && byte <= 126)
      return (char)byte;
   else
      return '?';
}

static void png_icc_tag_name ( char *  name, png_uint_32  tag  )

static

{
   name[0] = '\'';
   name[1] = png_icc_tag_char(tag >> 24);
   name[2] = png_icc_tag_char(tag >> 16);
   name[3] = png_icc_tag_char(tag >>  8);
   name[4] = png_icc_tag_char(tag      );
   name[5] = '\'';
}

static int is_ICC_signature_char ( png_alloc_size_t  it )

static

{
   return it == 32 || (it >= 48 && it <= 57) || (it >= 65 && it <= 90) ||
      (it >= 97 && it <= 122);
}

static int is_ICC_signature ( png_alloc_size_t  it )

static

{
   return is_ICC_signature_char(it >> 24) /* checks all the top bits */ &&
      is_ICC_signature_char((it >> 16) & 0xff) &&
      is_ICC_signature_char((it >> 8) & 0xff) &&
      is_ICC_signature_char(it & 0xff);
}

static int png_icc_profile_error ( png_const_structrp  png_ptr, png_colorspacerp  colorspace, png_const_charp  name, png_alloc_size_t  value, png_const_charp  reason  )

static

{
   size_t pos;
   char message[196]; /* see below for calculation */

   if (colorspace != NULL)
      colorspace->flags |= PNG_COLORSPACE_INVALID;

   pos = png_safecat(message, (sizeof message), 0, "profile '"); /* 9 chars */
   pos = png_safecat(message, pos+79, pos, name); /* Truncate to 79 chars */
   pos = png_safecat(message, (sizeof message), pos, "': "); /* +2 = 90 */
   if (is_ICC_signature(value) != 0)
   {
      /* So 'value' is at most 4 bytes and the following cast is safe */
      png_icc_tag_name(message+pos, (png_uint_32)value);
      pos += 6; /* total +8; less than the else clause */
      message[pos++] = ':';
      message[pos++] = ' ';
   }
#  ifdef PNG_WARNINGS_SUPPORTED
   else
      {
         char number[PNG_NUMBER_BUFFER_SIZE]; /* +24 = 114*/

         pos = png_safecat(message, (sizeof message), pos,
            png_format_number(number, number+(sizeof number),
               PNG_NUMBER_FORMAT_x, value));
         pos = png_safecat(message, (sizeof message), pos, "h: "); /*+2 = 116*/
      }
#  endif
   /* The 'reason' is an arbitrary message, allow +79 maximum 195 */
   pos = png_safecat(message, (sizeof message), pos, reason);
   PNG_UNUSED(pos)

   /* This is recoverable, but make it unconditionally an app_error on write to
    * avoid writing invalid ICC profiles into PNG files (i.e., we handle them
    * on read, with a warning, but on write unless the app turns off
    * application errors the PNG won't be written.)
    */
   png_chunk_report(png_ptr, message,
      (colorspace != NULL) ? PNG_CHUNK_ERROR : PNG_CHUNK_WRITE_ERROR);

   return 0;
}

int png_colorspace_set_sRGB	(	png_const_structrp	png_ptr,
		png_colorspacerp	colorspace,
		int	intent
	)

{
   /* sRGB sets known gamma, end points and (from the chunk) intent. */
   /* IMPORTANT: these are not necessarily the values found in an ICC profile
    * because ICC profiles store values adapted to a D50 environment; it is
    * expected that the ICC profile mediaWhitePointTag will be D50; see the
    * checks and code elsewhere to understand this better.
    *
    * These XYZ values, which are accurate to 5dp, produce rgb to gray
    * coefficients of (6968,23435,2366), which are reduced (because they add up
    * to 32769 not 32768) to (6968,23434,2366).  These are the values that
    * libpng has traditionally used (and are the best values given the 15bit
    * algorithm used by the rgb to gray code.)
    */
   static const png_XYZ sRGB_XYZ = /* D65 XYZ (*not* the D50 adapted values!) */
   {
      /* color      X      Y      Z */
      /* red   */ 41239, 21264,  1933,
      /* green */ 35758, 71517, 11919,
      /* blue  */ 18048,  7219, 95053
   };

   /* Do nothing if the colorspace is already invalidated. */
   if ((colorspace->flags & PNG_COLORSPACE_INVALID) != 0)
      return 0;

   /* Check the intent, then check for existing settings.  It is valid for the
    * PNG file to have cHRM or gAMA chunks along with sRGB, but the values must
    * be consistent with the correct values.  If, however, this function is
    * called below because an iCCP chunk matches sRGB then it is quite
    * conceivable that an older app recorded incorrect gAMA and cHRM because of
    * an incorrect calculation based on the values in the profile - this does
    * *not* invalidate the profile (though it still produces an error, which can
    * be ignored.)
    */
   if (intent < 0 || intent >= PNG_sRGB_INTENT_LAST)
      return png_icc_profile_error(png_ptr, colorspace, "sRGB",
         (unsigned)intent, "invalid sRGB rendering intent");

   if ((colorspace->flags & PNG_COLORSPACE_HAVE_INTENT) != 0 &&
      colorspace->rendering_intent != intent)
      return png_icc_profile_error(png_ptr, colorspace, "sRGB",
         (unsigned)intent, "inconsistent rendering intents");

   if ((colorspace->flags & PNG_COLORSPACE_FROM_sRGB) != 0)
   {
      png_benign_error(png_ptr, "duplicate sRGB information ignored");
      return 0;
   }

   /* If the standard sRGB cHRM chunk does not match the one from the PNG file
    * warn but overwrite the value with the correct one.
    */
   if ((colorspace->flags & PNG_COLORSPACE_HAVE_ENDPOINTS) != 0 &&
      !png_colorspace_endpoints_match(&sRGB_xy, &colorspace->end_points_xy,
         100))
      png_chunk_report(png_ptr, "cHRM chunk does not match sRGB",
         PNG_CHUNK_ERROR);

   /* This check is just done for the error reporting - the routine always
    * returns true when the 'from' argument corresponds to sRGB (2).
    */
   (void)png_colorspace_check_gamma(png_ptr, colorspace, PNG_GAMMA_sRGB_INVERSE,
      2/*from sRGB*/);

   /* intent: bugs in GCC force 'int' to be used as the parameter type. */
   colorspace->rendering_intent = (png_uint_16)intent;
   colorspace->flags |= PNG_COLORSPACE_HAVE_INTENT;

   /* endpoints */
   colorspace->end_points_xy = sRGB_xy;
   colorspace->end_points_XYZ = sRGB_XYZ;
   colorspace->flags |=
      (PNG_COLORSPACE_HAVE_ENDPOINTS|PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB);

   /* gamma */
   colorspace->gamma = PNG_GAMMA_sRGB_INVERSE;
   colorspace->flags |= PNG_COLORSPACE_HAVE_GAMMA;

   /* Finally record that we have an sRGB profile */
   colorspace->flags |=
      (PNG_COLORSPACE_MATCHES_sRGB|PNG_COLORSPACE_FROM_sRGB);

   return 1; /* set */
}

int png_icc_check_length	(	png_const_structrp	png_ptr,
		png_colorspacerp	colorspace,
		png_const_charp	name,
		png_uint_32	profile_length
	)

{
   if (profile_length < 132)
      return png_icc_profile_error(png_ptr, colorspace, name, profile_length,
         "too short");

   return 1;
}

int png_icc_check_header	(	png_const_structrp	png_ptr,
		png_colorspacerp	colorspace,
		png_const_charp	name,
		png_uint_32	profile_length,
		png_const_bytep	profile,
		int	color_type
	)

{
   png_uint_32 temp;

   /* Length check; this cannot be ignored in this code because profile_length
    * is used later to check the tag table, so even if the profile seems over
    * long profile_length from the caller must be correct.  The caller can fix
    * this up on read or write by just passing in the profile header length.
    */
   temp = png_get_uint_32(profile);
   if (temp != profile_length)
      return png_icc_profile_error(png_ptr, colorspace, name, temp,
         "length does not match profile");

   temp = (png_uint_32) (*(profile+8));
   if (temp > 3 && (profile_length & 3))
      return png_icc_profile_error(png_ptr, colorspace, name, profile_length,
         "invalid length");

   temp = png_get_uint_32(profile+128); /* tag count: 12 bytes/tag */
   if (temp > 357913930 || /* (2^32-4-132)/12: maximum possible tag count */
      profile_length < 132+12*temp) /* truncated tag table */
      return png_icc_profile_error(png_ptr, colorspace, name, temp,
         "tag count too large");

   /* The 'intent' must be valid or we can't store it, ICC limits the intent to
    * 16 bits.
    */
   temp = png_get_uint_32(profile+64);
   if (temp >= 0xffff) /* The ICC limit */
      return png_icc_profile_error(png_ptr, colorspace, name, temp,
         "invalid rendering intent");

   /* This is just a warning because the profile may be valid in future
    * versions.
    */
   if (temp >= PNG_sRGB_INTENT_LAST)
      (void)png_icc_profile_error(png_ptr, NULL, name, temp,
         "intent outside defined range");

   /* At this point the tag table can't be checked because it hasn't necessarily
    * been loaded; however, various header fields can be checked.  These checks
    * are for values permitted by the PNG spec in an ICC profile; the PNG spec
    * restricts the profiles that can be passed in an iCCP chunk (they must be
    * appropriate to processing PNG data!)
    */

   /* Data checks (could be skipped).  These checks must be independent of the
    * version number; however, the version number doesn't accomodate changes in
    * the header fields (just the known tags and the interpretation of the
    * data.)
    */
   temp = png_get_uint_32(profile+36); /* signature 'ascp' */
   if (temp != 0x61637370)
      return png_icc_profile_error(png_ptr, colorspace, name, temp,
         "invalid signature");

   /* Currently the PCS illuminant/adopted white point (the computational
    * white point) are required to be D50,
    * however the profile contains a record of the illuminant so perhaps ICC
    * expects to be able to change this in the future (despite the rationale in
    * the introduction for using a fixed PCS adopted white.)  Consequently the
    * following is just a warning.
    */
   if (memcmp(profile+68, D50_nCIEXYZ, 12) != 0)
      (void)png_icc_profile_error(png_ptr, NULL, name, 0/*no tag value*/,
         "PCS illuminant is not D50");

   /* The PNG spec requires this:
    * "If the iCCP chunk is present, the image samples conform to the colour
    * space represented by the embedded ICC profile as defined by the
    * International Color Consortium [ICC]. The colour space of the ICC profile
    * shall be an RGB colour space for colour images (PNG colour types 2, 3, and
    * 6), or a greyscale colour space for greyscale images (PNG colour types 0
    * and 4)."
    *
    * This checking code ensures the embedded profile (on either read or write)
    * conforms to the specification requirements.  Notice that an ICC 'gray'
    * color-space profile contains the information to transform the monochrome
    * data to XYZ or L*a*b (according to which PCS the profile uses) and this
    * should be used in preference to the standard libpng K channel replication
    * into R, G and B channels.
    *
    * Previously it was suggested that an RGB profile on grayscale data could be
    * handled.  However it it is clear that using an RGB profile in this context
    * must be an error - there is no specification of what it means.  Thus it is
    * almost certainly more correct to ignore the profile.
    */
   temp = png_get_uint_32(profile+16); /* data colour space field */
   switch (temp)
   {
      case 0x52474220: /* 'RGB ' */
         if ((color_type & PNG_COLOR_MASK_COLOR) == 0)
            return png_icc_profile_error(png_ptr, colorspace, name, temp,
               "RGB color space not permitted on grayscale PNG");
         break;

      case 0x47524159: /* 'GRAY' */
         if ((color_type & PNG_COLOR_MASK_COLOR) != 0)
            return png_icc_profile_error(png_ptr, colorspace, name, temp,
               "Gray color space not permitted on RGB PNG");
         break;

      default:
         return png_icc_profile_error(png_ptr, colorspace, name, temp,
            "invalid ICC profile color space");
   }

   /* It is up to the application to check that the profile class matches the
    * application requirements; the spec provides no guidance, but it's pretty
    * weird if the profile is not scanner ('scnr'), monitor ('mntr'), printer
    * ('prtr') or 'spac' (for generic color spaces).  Issue a warning in these
    * cases.  Issue an error for device link or abstract profiles - these don't
    * contain the records necessary to transform the color-space to anything
    * other than the target device (and not even that for an abstract profile).
    * Profiles of these classes may not be embedded in images.
    */
   temp = png_get_uint_32(profile+12); /* profile/device class */
   switch (temp)
   {
      case 0x73636E72: /* 'scnr' */
      case 0x6D6E7472: /* 'mntr' */
      case 0x70727472: /* 'prtr' */
      case 0x73706163: /* 'spac' */
         /* All supported */
         break;

      case 0x61627374: /* 'abst' */
         /* May not be embedded in an image */
         return png_icc_profile_error(png_ptr, colorspace, name, temp,
            "invalid embedded Abstract ICC profile");

      case 0x6C696E6B: /* 'link' */
         /* DeviceLink profiles cannot be interpreted in a non-device specific
          * fashion, if an app uses the AToB0Tag in the profile the results are
          * undefined unless the result is sent to the intended device,
          * therefore a DeviceLink profile should not be found embedded in a
          * PNG.
          */
         return png_icc_profile_error(png_ptr, colorspace, name, temp,
            "unexpected DeviceLink ICC profile class");

      case 0x6E6D636C: /* 'nmcl' */
         /* A NamedColor profile is also device specific, however it doesn't
          * contain an AToB0 tag that is open to misinterpretation.  Almost
          * certainly it will fail the tests below.
          */
         (void)png_icc_profile_error(png_ptr, NULL, name, temp,
            "unexpected NamedColor ICC profile class");
         break;

      default:
         /* To allow for future enhancements to the profile accept unrecognized
          * profile classes with a warning, these then hit the test below on the
          * tag content to ensure they are backward compatible with one of the
          * understood profiles.
          */
         (void)png_icc_profile_error(png_ptr, NULL, name, temp,
            "unrecognized ICC profile class");
         break;
   }

   /* For any profile other than a device link one the PCS must be encoded
    * either in XYZ or Lab.
    */
   temp = png_get_uint_32(profile+20);
   switch (temp)
   {
      case 0x58595A20: /* 'XYZ ' */
      case 0x4C616220: /* 'Lab ' */
         break;

      default:
         return png_icc_profile_error(png_ptr, colorspace, name, temp,
            "unexpected ICC PCS encoding");
   }

   return 1;
}

int png_icc_check_tag_table	(	png_const_structrp	png_ptr,
		png_colorspacerp	colorspace,
		png_const_charp	name,
		png_uint_32	profile_length,
		png_const_bytep	profile
	)

{
   png_uint_32 tag_count = png_get_uint_32(profile+128);
   png_uint_32 itag;
   png_const_bytep tag = profile+132; /* The first tag */

   /* First scan all the tags in the table and add bits to the icc_info value
    * (temporarily in 'tags').
    */
   for (itag=0; itag < tag_count; ++itag, tag += 12)
   {
      png_uint_32 tag_id = png_get_uint_32(tag+0);
      png_uint_32 tag_start = png_get_uint_32(tag+4); /* must be aligned */
      png_uint_32 tag_length = png_get_uint_32(tag+8);/* not padded */

      /* The ICC specification does not exclude zero length tags, therefore the
       * start might actually be anywhere if there is no data, but this would be
       * a clear abuse of the intent of the standard so the start is checked for
       * being in range.  All defined tag types have an 8 byte header - a 4 byte
       * type signature then 0.
       */
      if ((tag_start & 3) != 0)
      {
         /* CNHP730S.icc shipped with Microsoft Windows 64 violates this, it is
          * only a warning here because libpng does not care about the
          * alignment.
          */
         (void)png_icc_profile_error(png_ptr, NULL, name, tag_id,
            "ICC profile tag start not a multiple of 4");
      }

      /* This is a hard error; potentially it can cause read outside the
       * profile.
       */
      if (tag_start > profile_length || tag_length > profile_length - tag_start)
         return png_icc_profile_error(png_ptr, colorspace, name, tag_id,
            "ICC profile tag outside profile");
   }

   return 1; /* success, maybe with warnings */
}

static int png_compare_ICC_profile_with_sRGB ( png_const_structrp  png_ptr, png_const_bytep  profile, uLong  adler  )

static

{
   /* The quick check is to verify just the MD5 signature and trust the
    * rest of the data.  Because the profile has already been verified for
    * correctness this is safe.  png_colorspace_set_sRGB will check the 'intent'
    * field too, so if the profile has been edited with an intent not defined
    * by sRGB (but maybe defined by a later ICC specification) the read of
    * the profile will fail at that point.
    */

   png_uint_32 length = 0;
   png_uint_32 intent = 0x10000; /* invalid */
#if PNG_sRGB_PROFILE_CHECKS > 1
   uLong crc = 0; /* the value for 0 length data */
#endif
   unsigned int i;

#ifdef PNG_SET_OPTION_SUPPORTED
   /* First see if PNG_SKIP_sRGB_CHECK_PROFILE has been set to "on" */
   if (((png_ptr->options >> PNG_SKIP_sRGB_CHECK_PROFILE) & 3) ==
               PNG_OPTION_ON)
      return 0;
#endif

   for (i=0; i < (sizeof png_sRGB_checks) / (sizeof png_sRGB_checks[0]); ++i)
   {
      if (png_get_uint_32(profile+84) == png_sRGB_checks[i].md5[0] &&
         png_get_uint_32(profile+88) == png_sRGB_checks[i].md5[1] &&
         png_get_uint_32(profile+92) == png_sRGB_checks[i].md5[2] &&
         png_get_uint_32(profile+96) == png_sRGB_checks[i].md5[3])
      {
         /* This may be one of the old HP profiles without an MD5, in that
          * case we can only use the length and Adler32 (note that these
          * are not used by default if there is an MD5!)
          */
#        if PNG_sRGB_PROFILE_CHECKS == 0
            if (png_sRGB_checks[i].have_md5 != 0)
               return 1+png_sRGB_checks[i].is_broken;
#        endif

         /* Profile is unsigned or more checks have been configured in. */
         if (length == 0)
         {
            length = png_get_uint_32(profile);
            intent = png_get_uint_32(profile+64);
         }

         /* Length *and* intent must match */
         if (length == png_sRGB_checks[i].length &&
            intent == png_sRGB_checks[i].intent)
         {
            /* Now calculate the adler32 if not done already. */
            if (adler == 0)
            {
               adler = adler32(0, NULL, 0);
               adler = adler32(adler, profile, length);
            }

            if (adler == png_sRGB_checks[i].adler)
            {
               /* These basic checks suggest that the data has not been
                * modified, but if the check level is more than 1 perform
                * our own crc32 checksum on the data.
                */
#              if PNG_sRGB_PROFILE_CHECKS > 1
                  if (crc == 0)
                  {
                     crc = crc32(0, NULL, 0);
                     crc = crc32(crc, profile, length);
                  }

                  /* So this check must pass for the 'return' below to happen.
                   */
                  if (crc == png_sRGB_checks[i].crc)
#              endif
               {
                  if (png_sRGB_checks[i].is_broken != 0)
                  {
                     /* These profiles are known to have bad data that may cause
                      * problems if they are used, therefore attempt to
                      * discourage their use, skip the 'have_md5' warning below,
                      * which is made irrelevant by this error.
                      */
                     png_chunk_report(png_ptr, "known incorrect sRGB profile",
                        PNG_CHUNK_ERROR);
                  }

                  /* Warn that this being done; this isn't even an error since
                   * the profile is perfectly valid, but it would be nice if
                   * people used the up-to-date ones.
                   */
                  else if (png_sRGB_checks[i].have_md5 == 0)
                  {
                     png_chunk_report(png_ptr, "out-of-date sRGB profile with"
                        " no signature",
                        PNG_CHUNK_WARNING);
                  }

                  return 1+png_sRGB_checks[i].is_broken;
               }
            }

# if PNG_sRGB_PROFILE_CHECKS > 0
         /* The signature matched, but the profile had been changed in some
          * way.  This probably indicates a data error or uninformed hacking.
          * Fall through to "no match".
          */
         png_chunk_report(png_ptr, "Not recognizing known sRGB profile that"
             " has been edited", 
             PNG_CHUNK_WARNING);
         break;
# endif
         }
      }
   }

   return 0; /* no match */
}

void png_icc_set_sRGB	(	png_const_structrp	png_ptr,
		png_colorspacerp	colorspace,
		png_const_bytep	profile,
		uLong	adler
	)

{
   /* Is this profile one of the known ICC sRGB profiles?  If it is, just set
    * the sRGB information.
    */
#if PNG_sRGB_PROFILE_CHECKS >= 0
   if (png_compare_ICC_profile_with_sRGB(png_ptr, profile, adler) != 0)
#endif
      (void)png_colorspace_set_sRGB(png_ptr, colorspace,
         (int)/*already checked*/png_get_uint_32(profile+64));
}

int png_colorspace_set_ICC	(	png_const_structrp	png_ptr,
		png_colorspacerp	colorspace,
		png_const_charp	name,
		png_uint_32	profile_length,
		png_const_bytep	profile,
		int	color_type
	)

{
   if ((colorspace->flags & PNG_COLORSPACE_INVALID) != 0)
      return 0;

   if (png_icc_check_length(png_ptr, colorspace, name, profile_length) != 0 &&
       png_icc_check_header(png_ptr, colorspace, name, profile_length, profile,
          color_type) != 0 &&
       png_icc_check_tag_table(png_ptr, colorspace, name, profile_length,
          profile) != 0)
   {
#     ifdef PNG_sRGB_SUPPORTED
         /* If no sRGB support, don't try storing sRGB information */
         png_icc_set_sRGB(png_ptr, colorspace, profile, 0);
#     endif
      return 1;
   }

   /* Failure case */
   return 0;
}

void png_colorspace_set_rgb_coefficients

(

png_structrp

png_ptr

)

{
   /* Set the rgb_to_gray coefficients from the colorspace. */
   if (png_ptr->rgb_to_gray_coefficients_set == 0 &&
      (png_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_ENDPOINTS) != 0)
   {
      /* png_set_background has not been called, get the coefficients from the Y
       * values of the colorspace colorants.
       */
      png_fixed_point r = png_ptr->colorspace.end_points_XYZ.red_Y;
      png_fixed_point g = png_ptr->colorspace.end_points_XYZ.green_Y;
      png_fixed_point b = png_ptr->colorspace.end_points_XYZ.blue_Y;
      png_fixed_point total = r+g+b;

      if (total > 0 &&
         r >= 0 && png_muldiv(&r, r, 32768, total) && r >= 0 && r <= 32768 &&
         g >= 0 && png_muldiv(&g, g, 32768, total) && g >= 0 && g <= 32768 &&
         b >= 0 && png_muldiv(&b, b, 32768, total) && b >= 0 && b <= 32768 &&
         r+g+b <= 32769)
      {
         /* We allow 0 coefficients here.  r+g+b may be 32769 if two or
          * all of the coefficients were rounded up.  Handle this by
          * reducing the *largest* coefficient by 1; this matches the
          * approach used for the default coefficients in pngrtran.c
          */
         int add = 0;

         if (r+g+b > 32768)
            add = -1;
         else if (r+g+b < 32768)
            add = 1;

         if (add != 0)
         {
            if (g >= r && g >= b)
               g += add;
            else if (r >= g && r >= b)
               r += add;
            else
               b += add;
         }

         /* Check for an internal error. */
         if (r+g+b != 32768)
            png_error(png_ptr,
               "internal error handling cHRM coefficients");

         else
         {
            png_ptr->rgb_to_gray_red_coeff   = (png_uint_16)r;
            png_ptr->rgb_to_gray_green_coeff = (png_uint_16)g;
         }
      }

      /* This is a png_error at present even though it could be ignored -
       * it should never happen, but it is important that if it does, the
       * bug is fixed.
       */
      else
         png_error(png_ptr, "internal error handling cHRM->XYZ");
   }
}

void png_check_IHDR	(	png_const_structrp	png_ptr,
		png_uint_32	width,
		png_uint_32	height,
		int	bit_depth,
		int	color_type,
		int	interlace_type,
		int	compression_type,
		int	filter_type
	)

{
   int error = 0;

   /* Check for width and height valid values */
   if (width == 0)
   {
      png_warning(png_ptr, "Image width is zero in IHDR");
      error = 1;
   }
   else if (width > PNG_UINT_31_MAX)
   {
      png_warning(png_ptr, "Invalid image width in IHDR");
      error = 1;
   }

   else if (png_gt(width,
                   (PNG_SIZE_MAX >> 3) /* 8-byte RGBA pixels */
                   - 48                /* big_row_buf hack */
                   - 1                 /* filter byte */
                   - 7*8               /* rounding width to multiple of 8 pix */
                   - 8))               /* extra max_pixel_depth pad */
   {
      /* The size of the row must be within the limits of this architecture.
       * Because the read code can perform arbitrary transformations the
       * maximum size is checked here.  Because the code in png_read_start_row
       * adds extra space "for safety's sake" in several places a conservative
       * limit is used here.
       *
       * NOTE: it would be far better to check the size that is actually used,
       * but the effect in the real world is minor and the changes are more
       * extensive, therefore much more dangerous and much more difficult to
       * write in a way that avoids compiler warnings.
       */
      png_warning(png_ptr, "Image width is too large for this architecture");
      error = 1;
   }
   else
   {
#     ifdef PNG_SET_USER_LIMITS_SUPPORTED
      if (width > png_ptr->user_width_max)
#     else
      if (width > PNG_USER_WIDTH_MAX)
#     endif
      {
         png_warning(png_ptr, "Image width exceeds user limit in IHDR");
         error = 1;
      }
   }

   if (height == 0)
   {
      png_warning(png_ptr, "Image height is zero in IHDR");
      error = 1;
   }
   else if (height > PNG_UINT_31_MAX)
   {
      png_warning(png_ptr, "Invalid image height in IHDR");
      error = 1;
   }
   else
   {
#     ifdef PNG_SET_USER_LIMITS_SUPPORTED
      if (height > png_ptr->user_height_max)
#     else
      if (height > PNG_USER_HEIGHT_MAX)
#     endif
      {
         png_warning(png_ptr, "Image height exceeds user limit in IHDR");
         error = 1;
      }
   }

   /* Check other values */
   if (bit_depth != 1 && bit_depth != 2 && bit_depth != 4 &&
       bit_depth != 8 && bit_depth != 16)
   {
      png_warning(png_ptr, "Invalid bit depth in IHDR");
      error = 1;
   }

   if (color_type < 0 || color_type == 1 ||
       color_type == 5 || color_type > 6)
   {
      png_warning(png_ptr, "Invalid color type in IHDR");
      error = 1;
   }

   if (((color_type == PNG_COLOR_TYPE_PALETTE) && bit_depth > 8) ||
       ((color_type == PNG_COLOR_TYPE_RGB ||
         color_type == PNG_COLOR_TYPE_GRAY_ALPHA ||
         color_type == PNG_COLOR_TYPE_RGB_ALPHA) && bit_depth < 8))
   {
      png_warning(png_ptr, "Invalid color type/bit depth combination in IHDR");
      error = 1;
   }

   if (interlace_type >= PNG_INTERLACE_LAST)
   {
      png_warning(png_ptr, "Unknown interlace method in IHDR");
      error = 1;
   }

   if (compression_type != PNG_COMPRESSION_TYPE_BASE)
   {
      png_warning(png_ptr, "Unknown compression method in IHDR");
      error = 1;
   }

#  ifdef PNG_MNG_FEATURES_SUPPORTED
   /* Accept filter_method 64 (intrapixel differencing) only if
    * 1. Libpng was compiled with PNG_MNG_FEATURES_SUPPORTED and
    * 2. Libpng did not read a PNG signature (this filter_method is only
    *    used in PNG datastreams that are embedded in MNG datastreams) and
    * 3. The application called png_permit_mng_features with a mask that
    *    included PNG_FLAG_MNG_FILTER_64 and
    * 4. The filter_method is 64 and
    * 5. The color_type is RGB or RGBA
    */
   if ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) != 0 &&
       png_ptr->mng_features_permitted != 0)
      png_warning(png_ptr, "MNG features are not allowed in a PNG datastream");

   if (filter_type != PNG_FILTER_TYPE_BASE)
   {
      if (!((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) != 0 &&
          (filter_type == PNG_INTRAPIXEL_DIFFERENCING) &&
          ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) == 0) &&
          (color_type == PNG_COLOR_TYPE_RGB ||
          color_type == PNG_COLOR_TYPE_RGB_ALPHA)))
      {
         png_warning(png_ptr, "Unknown filter method in IHDR");
         error = 1;
      }

      if ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) != 0)
      {
         png_warning(png_ptr, "Invalid filter method in IHDR");
         error = 1;
      }
   }

#  else
   if (filter_type != PNG_FILTER_TYPE_BASE)
   {
      png_warning(png_ptr, "Unknown filter method in IHDR");
      error = 1;
   }
#  endif

   if (error == 1)
      png_error(png_ptr, "Invalid IHDR data");
}

int png_check_fp_number	(	png_const_charp	string,
		png_size_t	size,
		int *	statep,
		png_size_tp	whereami
	)

{
   int state = *statep;
   png_size_t i = *whereami;

   while (i < size)
   {
      int type;
      /* First find the type of the next character */
      switch (string[i])
      {
      case 43:  type = PNG_FP_SAW_SIGN;                   break;
      case 45:  type = PNG_FP_SAW_SIGN + PNG_FP_NEGATIVE; break;
      case 46:  type = PNG_FP_SAW_DOT;                    break;
      case 48:  type = PNG_FP_SAW_DIGIT;                  break;
      case 49: case 50: case 51: case 52:
      case 53: case 54: case 55: case 56:
      case 57:  type = PNG_FP_SAW_DIGIT + PNG_FP_NONZERO; break;
      case 69:
      case 101: type = PNG_FP_SAW_E;                      break;
      default:  goto PNG_FP_End;
      }

      /* Now deal with this type according to the current
       * state, the type is arranged to not overlap the
       * bits of the PNG_FP_STATE.
       */
      switch ((state & PNG_FP_STATE) + (type & PNG_FP_SAW_ANY))
      {
      case PNG_FP_INTEGER + PNG_FP_SAW_SIGN:
         if ((state & PNG_FP_SAW_ANY) != 0)
            goto PNG_FP_End; /* not a part of the number */

         png_fp_add(state, type);
         break;

      case PNG_FP_INTEGER + PNG_FP_SAW_DOT:
         /* Ok as trailer, ok as lead of fraction. */
         if ((state & PNG_FP_SAW_DOT) != 0) /* two dots */
            goto PNG_FP_End;

         else if ((state & PNG_FP_SAW_DIGIT) != 0) /* trailing dot? */
            png_fp_add(state, type);

         else
            png_fp_set(state, PNG_FP_FRACTION | type);

         break;

      case PNG_FP_INTEGER + PNG_FP_SAW_DIGIT:
         if ((state & PNG_FP_SAW_DOT) != 0) /* delayed fraction */
            png_fp_set(state, PNG_FP_FRACTION | PNG_FP_SAW_DOT);

         png_fp_add(state, type | PNG_FP_WAS_VALID);

         break;

      case PNG_FP_INTEGER + PNG_FP_SAW_E:
         if ((state & PNG_FP_SAW_DIGIT) == 0)
            goto PNG_FP_End;

         png_fp_set(state, PNG_FP_EXPONENT);

         break;

   /* case PNG_FP_FRACTION + PNG_FP_SAW_SIGN:
         goto PNG_FP_End; ** no sign in fraction */

   /* case PNG_FP_FRACTION + PNG_FP_SAW_DOT:
         goto PNG_FP_End; ** Because SAW_DOT is always set */

      case PNG_FP_FRACTION + PNG_FP_SAW_DIGIT:
         png_fp_add(state, type | PNG_FP_WAS_VALID);
         break;

      case PNG_FP_FRACTION + PNG_FP_SAW_E:
         /* This is correct because the trailing '.' on an
          * integer is handled above - so we can only get here
          * with the sequence ".E" (with no preceding digits).
          */
         if ((state & PNG_FP_SAW_DIGIT) == 0)
            goto PNG_FP_End;

         png_fp_set(state, PNG_FP_EXPONENT);

         break;

      case PNG_FP_EXPONENT + PNG_FP_SAW_SIGN:
         if ((state & PNG_FP_SAW_ANY) != 0)
            goto PNG_FP_End; /* not a part of the number */

         png_fp_add(state, PNG_FP_SAW_SIGN);

         break;

   /* case PNG_FP_EXPONENT + PNG_FP_SAW_DOT:
         goto PNG_FP_End; */

      case PNG_FP_EXPONENT + PNG_FP_SAW_DIGIT:
         png_fp_add(state, PNG_FP_SAW_DIGIT | PNG_FP_WAS_VALID);

         break;

   /* case PNG_FP_EXPONEXT + PNG_FP_SAW_E:
         goto PNG_FP_End; */

      default: goto PNG_FP_End; /* I.e. break 2 */
      }

      /* The character seems ok, continue. */
      ++i;
   }

PNG_FP_End:
   /* Here at the end, update the state and return the correct
    * return code.
    */
   *statep = state;
   *whereami = i;

   return (state & PNG_FP_SAW_DIGIT) != 0;
}

int png_check_fp_string	(	png_const_charp	string,
		png_size_t	size
	)

{
   int        state=0;
   png_size_t char_index=0;

   if (png_check_fp_number(string, size, &state, &char_index) != 0 &&
      (char_index == size || string[char_index] == 0))
      return state /* must be non-zero - see above */;

   return 0; /* i.e. fail */
}

static double png_pow10 ( int  power )

static

{
   int recip = 0;
   double d = 1;

   /* Handle negative exponent with a reciprocal at the end because
    * 10 is exact whereas .1 is inexact in base 2
    */
   if (power < 0)
   {
      if (power < DBL_MIN_10_EXP) return 0;
      recip = 1, power = -power;
   }

   if (power > 0)
   {
      /* Decompose power bitwise. */
      double mult = 10;
      do
      {
         if (power & 1) d *= mult;
         mult *= mult;
         power >>= 1;
      }
      while (power > 0);

      if (recip != 0) d = 1/d;
   }
   /* else power is 0 and d is 1 */

   return d;
}

void png_ascii_from_fp	(	png_const_structrp	png_ptr,
		png_charp	ascii,
		png_size_t	size,
		double	fp,
		unsigned int	precision
	)

{
   /* We use standard functions from math.h, but not printf because
    * that would require stdio.  The caller must supply a buffer of
    * sufficient size or we will png_error.  The tests on size and
    * the space in ascii[] consumed are indicated below.
    */
   if (precision < 1)
      precision = DBL_DIG;

   /* Enforce the limit of the implementation precision too. */
   if (precision > DBL_DIG+1)
      precision = DBL_DIG+1;

   /* Basic sanity checks */
   if (size >= precision+5) /* See the requirements below. */
   {
      if (fp < 0)
      {
         fp = -fp;
         *ascii++ = 45; /* '-'  PLUS 1 TOTAL 1 */
         --size;
      }

      if (fp >= DBL_MIN && fp <= DBL_MAX)
      {
         int exp_b10;       /* A base 10 exponent */
         double base;   /* 10^exp_b10 */

         /* First extract a base 10 exponent of the number,
          * the calculation below rounds down when converting
          * from base 2 to base 10 (multiply by log10(2) -
          * 0.3010, but 77/256 is 0.3008, so exp_b10 needs to
          * be increased.  Note that the arithmetic shift
          * performs a floor() unlike C arithmetic - using a
          * C multiply would break the following for negative
          * exponents.
          */
         (void)frexp(fp, &exp_b10); /* exponent to base 2 */

         exp_b10 = (exp_b10 * 77) >> 8; /* <= exponent to base 10 */

         /* Avoid underflow here. */
         base = png_pow10(exp_b10); /* May underflow */

         while (base < DBL_MIN || base < fp)
         {
            /* And this may overflow. */
            double test = png_pow10(exp_b10+1);

            if (test <= DBL_MAX)
               ++exp_b10, base = test;

            else
               break;
         }

         /* Normalize fp and correct exp_b10, after this fp is in the
          * range [.1,1) and exp_b10 is both the exponent and the digit
          * *before* which the decimal point should be inserted
          * (starting with 0 for the first digit).  Note that this
          * works even if 10^exp_b10 is out of range because of the
          * test on DBL_MAX above.
          */
         fp /= base;
         while (fp >= 1) fp /= 10, ++exp_b10;

         /* Because of the code above fp may, at this point, be
          * less than .1, this is ok because the code below can
          * handle the leading zeros this generates, so no attempt
          * is made to correct that here.
          */

         {
            int czero, clead, cdigits;
            char exponent[10];

            /* Allow up to two leading zeros - this will not lengthen
             * the number compared to using E-n.
             */
            if (exp_b10 < 0 && exp_b10 > -3) /* PLUS 3 TOTAL 4 */
            {
               czero = -exp_b10; /* PLUS 2 digits: TOTAL 3 */
               exp_b10 = 0;      /* Dot added below before first output. */
            }
            else
               czero = 0;    /* No zeros to add */

            /* Generate the digit list, stripping trailing zeros and
             * inserting a '.' before a digit if the exponent is 0.
             */
            clead = czero; /* Count of leading zeros */
            cdigits = 0;   /* Count of digits in list. */

            do
            {
               double d;

               fp *= 10;
               /* Use modf here, not floor and subtract, so that
                * the separation is done in one step.  At the end
                * of the loop don't break the number into parts so
                * that the final digit is rounded.
                */
               if (cdigits+czero-clead+1 < (int)precision)
                  fp = modf(fp, &d);

               else
               {
                  d = floor(fp + .5);

                  if (d > 9)
                  {
                     /* Rounding up to 10, handle that here. */
                     if (czero > 0)
                     {
                        --czero, d = 1;
                        if (cdigits == 0) --clead;
                     }
                     else
                     {
                        while (cdigits > 0 && d > 9)
                        {
                           int ch = *--ascii;

                           if (exp_b10 != (-1))
                              ++exp_b10;

                           else if (ch == 46)
                           {
                              ch = *--ascii, ++size;
                              /* Advance exp_b10 to '1', so that the
                               * decimal point happens after the
                               * previous digit.
                               */
                              exp_b10 = 1;
                           }

                           --cdigits;
                           d = ch - 47;  /* I.e. 1+(ch-48) */
                        }

                        /* Did we reach the beginning? If so adjust the
                         * exponent but take into account the leading
                         * decimal point.
                         */
                        if (d > 9)  /* cdigits == 0 */
                        {
                           if (exp_b10 == (-1))
                           {
                              /* Leading decimal point (plus zeros?), if
                               * we lose the decimal point here it must
                               * be reentered below.
                               */
                              int ch = *--ascii;

                              if (ch == 46)
                                 ++size, exp_b10 = 1;

                              /* Else lost a leading zero, so 'exp_b10' is
                               * still ok at (-1)
                               */
                           }
                           else
                              ++exp_b10;

                           /* In all cases we output a '1' */
                           d = 1;
                        }
                     }
                  }
                  fp = 0; /* Guarantees termination below. */
               }

               if (d == 0)
               {
                  ++czero;
                  if (cdigits == 0) ++clead;
               }
               else
               {
                  /* Included embedded zeros in the digit count. */
                  cdigits += czero - clead;
                  clead = 0;

                  while (czero > 0)
                  {
                     /* exp_b10 == (-1) means we just output the decimal
                      * place - after the DP don't adjust 'exp_b10' any
                      * more!
                      */
                     if (exp_b10 != (-1))
                     {
                        if (exp_b10 == 0) *ascii++ = 46, --size;
                        /* PLUS 1: TOTAL 4 */
                        --exp_b10;
                     }
                     *ascii++ = 48, --czero;
                  }

                  if (exp_b10 != (-1))
                  {
                     if (exp_b10 == 0)
                        *ascii++ = 46, --size; /* counted above */

                     --exp_b10;
                  }
                  *ascii++ = (char)(48 + (int)d), ++cdigits;
               }
            }
            while (cdigits+czero-clead < (int)precision && fp > DBL_MIN);

            /* The total output count (max) is now 4+precision */

            /* Check for an exponent, if we don't need one we are
             * done and just need to terminate the string.  At
             * this point exp_b10==(-1) is effectively if flag - it got
             * to '-1' because of the decrement after outputing
             * the decimal point above (the exponent required is
             * *not* -1!)
             */
            if (exp_b10 >= (-1) && exp_b10 <= 2)
            {
               /* The following only happens if we didn't output the
                * leading zeros above for negative exponent, so this
                * doest add to the digit requirement.  Note that the
                * two zeros here can only be output if the two leading
                * zeros were *not* output, so this doesn't increase
                * the output count.
                */
               while (--exp_b10 >= 0) *ascii++ = 48;

               *ascii = 0;

               /* Total buffer requirement (including the '\0') is
                * 5+precision - see check at the start.
                */
               return;
            }

            /* Here if an exponent is required, adjust size for
             * the digits we output but did not count.  The total
             * digit output here so far is at most 1+precision - no
             * decimal point and no leading or trailing zeros have
             * been output.
             */
            size -= cdigits;

            *ascii++ = 69, --size;    /* 'E': PLUS 1 TOTAL 2+precision */

            /* The following use of an unsigned temporary avoids ambiguities in
             * the signed arithmetic on exp_b10 and permits GCC at least to do
             * better optimization.
             */
            {
               unsigned int uexp_b10;

               if (exp_b10 < 0)
               {
                  *ascii++ = 45, --size; /* '-': PLUS 1 TOTAL 3+precision */
                  uexp_b10 = -exp_b10;
               }

               else
                  uexp_b10 = exp_b10;

               cdigits = 0;

               while (uexp_b10 > 0)
               {
                  exponent[cdigits++] = (char)(48 + uexp_b10 % 10);
                  uexp_b10 /= 10;
               }
            }

            /* Need another size check here for the exponent digits, so
             * this need not be considered above.
             */
            if ((int)size > cdigits)
            {
               while (cdigits > 0) *ascii++ = exponent[--cdigits];

               *ascii = 0;

               return;
            }
         }
      }
      else if (!(fp >= DBL_MIN))
      {
         *ascii++ = 48; /* '0' */
         *ascii = 0;
         return;
      }
      else
      {
         *ascii++ = 105; /* 'i' */
         *ascii++ = 110; /* 'n' */
         *ascii++ = 102; /* 'f' */
         *ascii = 0;
         return;
      }
   }

   /* Here on buffer too small. */
   png_error(png_ptr, "ASCII conversion buffer too small");
}

void png_ascii_from_fixed	(	png_const_structrp	png_ptr,
		png_charp	ascii,
		png_size_t	size,
		png_fixed_point	fp
	)

{
   /* Require space for 10 decimal digits, a decimal point, a minus sign and a
    * trailing \0, 13 characters:
    */
   if (size > 12)
   {
      png_uint_32 num;

      /* Avoid overflow here on the minimum integer. */
      if (fp < 0)
         *ascii++ = 45, --size, num = -fp;
      else
         num = fp;

      if (num <= 0x80000000) /* else overflowed */
      {
         unsigned int ndigits = 0, first = 16 /* flag value */;
         char digits[10];

         while (num)
         {
            /* Split the low digit off num: */
            unsigned int tmp = num/10;
            num -= tmp*10;
            digits[ndigits++] = (char)(48 + num);
            /* Record the first non-zero digit, note that this is a number
             * starting at 1, it's not actually the array index.
             */
            if (first == 16 && num > 0)
               first = ndigits;
            num = tmp;
         }

         if (ndigits > 0)
         {
            while (ndigits > 5) *ascii++ = digits[--ndigits];
            /* The remaining digits are fractional digits, ndigits is '5' or
             * smaller at this point.  It is certainly not zero.  Check for a
             * non-zero fractional digit:
             */
            if (first <= 5)
            {
               unsigned int i;
               *ascii++ = 46; /* decimal point */
               /* ndigits may be <5 for small numbers, output leading zeros
                * then ndigits digits to first:
                */
               i = 5;
               while (ndigits < i) *ascii++ = 48, --i;
               while (ndigits >= first) *ascii++ = digits[--ndigits];
               /* Don't output the trailing zeros! */
            }
         }
         else
            *ascii++ = 48;

         /* And null terminate the string: */
         *ascii = 0;
         return;
      }
   }

   /* Here on buffer too small. */
   png_error(png_ptr, "ASCII conversion buffer too small");
}

png_fixed_point png_fixed	(	png_const_structrp	png_ptr,
		double	fp,
		png_const_charp	text
	)

{
   double r = floor(100000 * fp + .5);

   if (r > 2147483647. || r < -2147483648.)
      png_fixed_error(png_ptr, text);

#  ifndef PNG_ERROR_TEXT_SUPPORTED
      PNG_UNUSED(text)
#  endif

   return (png_fixed_point)r;
}

int png_muldiv	(	png_fixed_point_p	res,
		png_fixed_point	a,
		png_int_32	times,
		png_int_32	divisor
	)

{
   /* Return a * times / divisor, rounded. */
   if (divisor != 0)
   {
      if (a == 0 || times == 0)
      {
         *res = 0;
         return 1;
      }
      else
      {
#ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
         double r = a;
         r *= times;
         r /= divisor;
         r = floor(r+.5);

         /* A png_fixed_point is a 32-bit integer. */
         if (r <= 2147483647. && r >= -2147483648.)
         {
            *res = (png_fixed_point)r;
            return 1;
         }
#else
         int negative = 0;
         png_uint_32 A, T, D;
         png_uint_32 s16, s32, s00;

         if (a < 0)
            negative = 1, A = -a;
         else
            A = a;

         if (times < 0)
            negative = !negative, T = -times;
         else
            T = times;

         if (divisor < 0)
            negative = !negative, D = -divisor;
         else
            D = divisor;

         /* Following can't overflow because the arguments only
          * have 31 bits each, however the result may be 32 bits.
          */
         s16 = (A >> 16) * (T & 0xffff) +
                           (A & 0xffff) * (T >> 16);
         /* Can't overflow because the a*times bit is only 30
          * bits at most.
          */
         s32 = (A >> 16) * (T >> 16) + (s16 >> 16);
         s00 = (A & 0xffff) * (T & 0xffff);

         s16 = (s16 & 0xffff) << 16;
         s00 += s16;

         if (s00 < s16)
            ++s32; /* carry */

         if (s32 < D) /* else overflow */
         {
            /* s32.s00 is now the 64-bit product, do a standard
             * division, we know that s32 < D, so the maximum
             * required shift is 31.
             */
            int bitshift = 32;
            png_fixed_point result = 0; /* NOTE: signed */

            while (--bitshift >= 0)
            {
               png_uint_32 d32, d00;

               if (bitshift > 0)
                  d32 = D >> (32-bitshift), d00 = D << bitshift;

               else
                  d32 = 0, d00 = D;

               if (s32 > d32)
               {
                  if (s00 < d00) --s32; /* carry */
                  s32 -= d32, s00 -= d00, result += 1<<bitshift;
               }

               else
                  if (s32 == d32 && s00 >= d00)
                     s32 = 0, s00 -= d00, result += 1<<bitshift;
            }

            /* Handle the rounding. */
            if (s00 >= (D >> 1))
               ++result;

            if (negative != 0)
               result = -result;

            /* Check for overflow. */
            if ((negative != 0 && result <= 0) ||
                (negative == 0 && result >= 0))
            {
               *res = result;
               return 1;
            }
         }
#endif
      }
   }

   return 0;
}

png_fixed_point png_muldiv_warn	(	png_const_structrp	png_ptr,
		png_fixed_point	a,
		png_int_32	times,
		png_int_32	divisor
	)

{
   png_fixed_point result;

   if (png_muldiv(&result, a, times, divisor) != 0)
      return result;

   png_warning(png_ptr, "fixed point overflow ignored");
   return 0;
}

png_fixed_point png_reciprocal

(

png_fixed_point

a

)

{
#ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
   double r = floor(1E10/a+.5);

   if (r <= 2147483647. && r >= -2147483648.)
      return (png_fixed_point)r;
#else
   png_fixed_point res;

   if (png_muldiv(&res, 100000, 100000, a) != 0)
      return res;
#endif

   return 0; /* error/overflow */
}

int png_gamma_significant

(

png_fixed_point

gamma_val

)

{
   return gamma_val < PNG_FP_1 - PNG_GAMMA_THRESHOLD_FIXED ||
       gamma_val > PNG_FP_1 + PNG_GAMMA_THRESHOLD_FIXED;
}

static png_fixed_point png_product2 ( png_fixed_point  a, png_fixed_point  b  )

static

{
   /* The required result is 1/a * 1/b; the following preserves accuracy. */
#    ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
   double r = a * 1E-5;
   r *= b;
   r = floor(r+.5);

   if (r <= 2147483647. && r >= -2147483648.)
      return (png_fixed_point)r;
#    else
   png_fixed_point res;

   if (png_muldiv(&res, a, b, 100000) != 0)
      return res;
#    endif

   return 0; /* overflow */
}

png_fixed_point png_reciprocal2	(	png_fixed_point	a,
		png_fixed_point	b
	)

{
   /* The required result is 1/a * 1/b; the following preserves accuracy. */
#ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
   double r = 1E15/a;
   r /= b;
   r = floor(r+.5);

   if (r <= 2147483647. && r >= -2147483648.)
      return (png_fixed_point)r;
#else
   /* This may overflow because the range of png_fixed_point isn't symmetric,
    * but this API is only used for the product of file and screen gamma so it
    * doesn't matter that the smallest number it can produce is 1/21474, not
    * 1/100000
    */
   png_fixed_point res = png_product2(a, b);

   if (res != 0)
      return png_reciprocal(res);
#endif

   return 0; /* overflow */
}

png_byte png_gamma_8bit_correct	(	unsigned int	value,
		png_fixed_point	gamma_val
	)

{
   if (value > 0 && value < 255)
   {
#     ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
         /* 'value' is unsigned, ANSI-C90 requires the compiler to correctly
          * convert this to a floating point value.  This includes values that
          * would overflow if 'value' were to be converted to 'int'.
          *
          * Apparently GCC, however, does an intermediate conversion to (int)
          * on some (ARM) but not all (x86) platforms, possibly because of
          * hardware FP limitations.  (E.g. if the hardware conversion always
          * assumes the integer register contains a signed value.)  This results
          * in ANSI-C undefined behavior for large values.
          *
          * Other implementations on the same machine might actually be ANSI-C90
          * conformant and therefore compile spurious extra code for the large
          * values.
          *
          * We can be reasonably sure that an unsigned to float conversion
          * won't be faster than an int to float one.  Therefore this code
          * assumes responsibility for the undefined behavior, which it knows
          * can't happen because of the check above.
          *
          * Note the argument to this routine is an (unsigned int) because, on
          * 16-bit platforms, it is assigned a value which might be out of
          * range for an (int); that would result in undefined behavior in the
          * caller if the *argument* ('value') were to be declared (int).
          */
         double r = floor(255*pow((int)/*SAFE*/value/255.,gamma_val*.00001)+.5);
         return (png_byte)r;
#     else
         png_int_32 lg2 = png_log8bit(value);
         png_fixed_point res;

         if (png_muldiv(&res, gamma_val, lg2, PNG_FP_1) != 0)
            return png_exp8bit(res);

         /* Overflow. */
         value = 0;
#     endif
   }

   return (png_byte)value;
}

png_uint_16 png_gamma_16bit_correct	(	unsigned int	value,
		png_fixed_point	gamma_val
	)

{
   if (value > 0 && value < 65535)
   {
#     ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
         /* The same (unsigned int)->(double) constraints apply here as above,
          * however in this case the (unsigned int) to (int) conversion can
          * overflow on an ANSI-C90 compliant system so the cast needs to ensure
          * that this is not possible.
          */
         double r = floor(65535*pow((png_int_32)value/65535.,
                     gamma_val*.00001)+.5);
         return (png_uint_16)r;
#     else
         png_int_32 lg2 = png_log16bit(value);
         png_fixed_point res;

         if (png_muldiv(&res, gamma_val, lg2, PNG_FP_1) != 0)
            return png_exp16bit(res);

         /* Overflow. */
         value = 0;
#     endif
   }

   return (png_uint_16)value;
}

png_uint_16 png_gamma_correct	(	png_structrp	png_ptr,
		unsigned int	value,
		png_fixed_point	gamma_val
	)

{
   if (png_ptr->bit_depth == 8)
      return png_gamma_8bit_correct(value, gamma_val);

#ifdef PNG_16BIT_SUPPORTED
   else
      return png_gamma_16bit_correct(value, gamma_val);
#else
      /* should not reach this */
      return 0;
#endif /* 16BIT */
}

static void png_build_16bit_table ( png_structrp  png_ptr, png_uint_16pp *  ptable, const unsigned int  shift, const png_fixed_point  gamma_val  )

static

{
   /* Various values derived from 'shift': */
   PNG_CONST unsigned int num = 1U << (8U - shift);
#ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
   /* CSE the division and work round wacky GCC warnings (see the comments
    * in png_gamma_8bit_correct for where these come from.)
    */
   PNG_CONST double fmax = 1./(((png_int_32)1 << (16U - shift))-1);
#endif
   PNG_CONST unsigned int max = (1U << (16U - shift))-1U;
   PNG_CONST unsigned int max_by_2 = 1U << (15U-shift);
   unsigned int i;

   png_uint_16pp table = *ptable =
       (png_uint_16pp)png_calloc(png_ptr, num * (sizeof (png_uint_16p)));

   for (i = 0; i < num; i++)
   {
      png_uint_16p sub_table = table[i] =
          (png_uint_16p)png_malloc(png_ptr, 256 * (sizeof (png_uint_16)));

      /* The 'threshold' test is repeated here because it can arise for one of
       * the 16-bit tables even if the others don't hit it.
       */
      if (png_gamma_significant(gamma_val) != 0)
      {
         /* The old code would overflow at the end and this would cause the
          * 'pow' function to return a result >1, resulting in an
          * arithmetic error.  This code follows the spec exactly; ig is
          * the recovered input sample, it always has 8-16 bits.
          *
          * We want input * 65535/max, rounded, the arithmetic fits in 32
          * bits (unsigned) so long as max <= 32767.
          */
         unsigned int j;
         for (j = 0; j < 256; j++)
         {
            png_uint_32 ig = (j << (8-shift)) + i;
#           ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
               /* Inline the 'max' scaling operation: */
               /* See png_gamma_8bit_correct for why the cast to (int) is
                * required here.
                */
               double d = floor(65535.*pow(ig*fmax, gamma_val*.00001)+.5);
               sub_table[j] = (png_uint_16)d;
#           else
               if (shift != 0)
                  ig = (ig * 65535U + max_by_2)/max;

               sub_table[j] = png_gamma_16bit_correct(ig, gamma_val);
#           endif
         }
      }
      else
      {
         /* We must still build a table, but do it the fast way. */
         unsigned int j;

         for (j = 0; j < 256; j++)
         {
            png_uint_32 ig = (j << (8-shift)) + i;

            if (shift != 0)
               ig = (ig * 65535U + max_by_2)/max;

            sub_table[j] = (png_uint_16)ig;
         }
      }
   }
}

static void png_build_16to8_table ( png_structrp  png_ptr, png_uint_16pp *  ptable, const unsigned int  shift, const png_fixed_point  gamma_val  )

static

{
   PNG_CONST unsigned int num = 1U << (8U - shift);
   PNG_CONST unsigned int max = (1U << (16U - shift))-1U;
   unsigned int i;
   png_uint_32 last;

   png_uint_16pp table = *ptable =
       (png_uint_16pp)png_calloc(png_ptr, num * (sizeof (png_uint_16p)));

   /* 'num' is the number of tables and also the number of low bits of low
    * bits of the input 16-bit value used to select a table.  Each table is
    * itself indexed by the high 8 bits of the value.
    */
   for (i = 0; i < num; i++)
      table[i] = (png_uint_16p)png_malloc(png_ptr,
          256 * (sizeof (png_uint_16)));

   /* 'gamma_val' is set to the reciprocal of the value calculated above, so
    * pow(out,g) is an *input* value.  'last' is the last input value set.
    *
    * In the loop 'i' is used to find output values.  Since the output is
    * 8-bit there are only 256 possible values.  The tables are set up to
    * select the closest possible output value for each input by finding
    * the input value at the boundary between each pair of output values
    * and filling the table up to that boundary with the lower output
    * value.
    *
    * The boundary values are 0.5,1.5..253.5,254.5.  Since these are 9-bit
    * values the code below uses a 16-bit value in i; the values start at
    * 128.5 (for 0.5) and step by 257, for a total of 254 values (the last
    * entries are filled with 255).  Start i at 128 and fill all 'last'
    * table entries <= 'max'
    */
   last = 0;
   for (i = 0; i < 255; ++i) /* 8-bit output value */
   {
      /* Find the corresponding maximum input value */
      png_uint_16 out = (png_uint_16)(i * 257U); /* 16-bit output value */

      /* Find the boundary value in 16 bits: */
      png_uint_32 bound = png_gamma_16bit_correct(out+128U, gamma_val);

      /* Adjust (round) to (16-shift) bits: */
      bound = (bound * max + 32768U)/65535U + 1U;

      while (last < bound)
      {
         table[last & (0xffU >> shift)][last >> (8U - shift)] = out;
         last++;
      }
   }

   /* And fill in the final entries. */
   while (last < (num << 8))
   {
      table[last & (0xff >> shift)][last >> (8U - shift)] = 65535U;
      last++;
   }
}

static void png_build_8bit_table ( png_structrp  png_ptr, png_bytepp  ptable, const png_fixed_point  gamma_val  )

static

{
   unsigned int i;
   png_bytep table = *ptable = (png_bytep)png_malloc(png_ptr, 256);

   if (png_gamma_significant(gamma_val) != 0)
      for (i=0; i<256; i++)
         table[i] = png_gamma_8bit_correct(i, gamma_val);

   else
      for (i=0; i<256; ++i)
         table[i] = (png_byte)i;
}

void png_destroy_gamma_table

(

png_structrp

png_ptr

)

{
   png_free(png_ptr, png_ptr->gamma_table);
   png_ptr->gamma_table = NULL;

#ifdef PNG_16BIT_SUPPORTED
   if (png_ptr->gamma_16_table != NULL)
   {
      int i;
      int istop = (1 << (8 - png_ptr->gamma_shift));
      for (i = 0; i < istop; i++)
      {
         png_free(png_ptr, png_ptr->gamma_16_table[i]);
      }
   png_free(png_ptr, png_ptr->gamma_16_table);
   png_ptr->gamma_16_table = NULL;
   }
#endif /* 16BIT */

#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
   defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
   defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
   png_free(png_ptr, png_ptr->gamma_from_1);
   png_ptr->gamma_from_1 = NULL;
   png_free(png_ptr, png_ptr->gamma_to_1);
   png_ptr->gamma_to_1 = NULL;

#ifdef PNG_16BIT_SUPPORTED
   if (png_ptr->gamma_16_from_1 != NULL)
   {
      int i;
      int istop = (1 << (8 - png_ptr->gamma_shift));
      for (i = 0; i < istop; i++)
      {
         png_free(png_ptr, png_ptr->gamma_16_from_1[i]);
      }
   png_free(png_ptr, png_ptr->gamma_16_from_1);
   png_ptr->gamma_16_from_1 = NULL;
   }
   if (png_ptr->gamma_16_to_1 != NULL)
   {
      int i;
      int istop = (1 << (8 - png_ptr->gamma_shift));
      for (i = 0; i < istop; i++)
      {
         png_free(png_ptr, png_ptr->gamma_16_to_1[i]);
      }
   png_free(png_ptr, png_ptr->gamma_16_to_1);
   png_ptr->gamma_16_to_1 = NULL;
   }
#endif /* 16BIT */
#endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
}

void png_build_gamma_table	(	png_structrp	png_ptr,
		int	bit_depth
	)

{
  png_debug(1, "in png_build_gamma_table");

  /* Remove any existing table; this copes with multiple calls to
   * png_read_update_info.  The warning is because building the gamma tables
   * multiple times is a performance hit - it's harmless but the ability to call
   * png_read_update_info() multiple times is new in 1.5.6 so it seems sensible
   * to warn if the app introduces such a hit.
   */
  if (png_ptr->gamma_table != NULL || png_ptr->gamma_16_table != NULL)
  {
    png_warning(png_ptr, "gamma table being rebuilt");
    png_destroy_gamma_table(png_ptr);
  }

  if (bit_depth <= 8)
  {
     png_build_8bit_table(png_ptr, &png_ptr->gamma_table,
         png_ptr->screen_gamma > 0 ?  png_reciprocal2(png_ptr->colorspace.gamma,
         png_ptr->screen_gamma) : PNG_FP_1);

#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
   defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
   defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
     if ((png_ptr->transformations & (PNG_COMPOSE | PNG_RGB_TO_GRAY)) != 0)
     {
        png_build_8bit_table(png_ptr, &png_ptr->gamma_to_1,
            png_reciprocal(png_ptr->colorspace.gamma));

        png_build_8bit_table(png_ptr, &png_ptr->gamma_from_1,
            png_ptr->screen_gamma > 0 ?  png_reciprocal(png_ptr->screen_gamma) :
            png_ptr->colorspace.gamma/* Probably doing rgb_to_gray */);
     }
#endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
  }
#ifdef PNG_16BIT_SUPPORTED
  else
  {
     png_byte shift, sig_bit;

     if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) != 0)
     {
        sig_bit = png_ptr->sig_bit.red;

        if (png_ptr->sig_bit.green > sig_bit)
           sig_bit = png_ptr->sig_bit.green;

        if (png_ptr->sig_bit.blue > sig_bit)
           sig_bit = png_ptr->sig_bit.blue;
     }
     else
        sig_bit = png_ptr->sig_bit.gray;

     /* 16-bit gamma code uses this equation:
      *
      *   ov = table[(iv & 0xff) >> gamma_shift][iv >> 8]
      *
      * Where 'iv' is the input color value and 'ov' is the output value -
      * pow(iv, gamma).
      *
      * Thus the gamma table consists of up to 256 256-entry tables.  The table
      * is selected by the (8-gamma_shift) most significant of the low 8 bits of
      * the color value then indexed by the upper 8 bits:
      *
      *   table[low bits][high 8 bits]
      *
      * So the table 'n' corresponds to all those 'iv' of:
      *
      *   <all high 8-bit values><n << gamma_shift>..<(n+1 << gamma_shift)-1>
      *
      */
     if (sig_bit > 0 && sig_bit < 16U)
        shift = (png_byte)(16U - sig_bit); /* shift == insignificant bits */

     else
        shift = 0; /* keep all 16 bits */

     if ((png_ptr->transformations & (PNG_16_TO_8 | PNG_SCALE_16_TO_8)) != 0)
     {
        /* PNG_MAX_GAMMA_8 is the number of bits to keep - effectively
         * the significant bits in the *input* when the output will
         * eventually be 8 bits.  By default it is 11.
         */
        if (shift < (16U - PNG_MAX_GAMMA_8))
           shift = (16U - PNG_MAX_GAMMA_8);
     }

     if (shift > 8U)
        shift = 8U; /* Guarantees at least one table! */

     png_ptr->gamma_shift = shift;

     /* NOTE: prior to 1.5.4 this test used to include PNG_BACKGROUND (now
      * PNG_COMPOSE).  This effectively smashed the background calculation for
      * 16-bit output because the 8-bit table assumes the result will be reduced
      * to 8 bits.
      */
     if ((png_ptr->transformations & (PNG_16_TO_8 | PNG_SCALE_16_TO_8)) != 0)
         png_build_16to8_table(png_ptr, &png_ptr->gamma_16_table, shift,
         png_ptr->screen_gamma > 0 ? png_product2(png_ptr->colorspace.gamma,
         png_ptr->screen_gamma) : PNG_FP_1);

     else
         png_build_16bit_table(png_ptr, &png_ptr->gamma_16_table, shift,
         png_ptr->screen_gamma > 0 ? png_reciprocal2(png_ptr->colorspace.gamma,
         png_ptr->screen_gamma) : PNG_FP_1);

#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
   defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
   defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
     if ((png_ptr->transformations & (PNG_COMPOSE | PNG_RGB_TO_GRAY)) != 0)
     {
        png_build_16bit_table(png_ptr, &png_ptr->gamma_16_to_1, shift,
            png_reciprocal(png_ptr->colorspace.gamma));

        /* Notice that the '16 from 1' table should be full precision, however
         * the lookup on this table still uses gamma_shift, so it can't be.
         * TODO: fix this.
         */
        png_build_16bit_table(png_ptr, &png_ptr->gamma_16_from_1, shift,
            png_ptr->screen_gamma > 0 ? png_reciprocal(png_ptr->screen_gamma) :
            png_ptr->colorspace.gamma/* Probably doing rgb_to_gray */);
     }
#endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
  }
#endif /* 16BIT */
}

int png_set_option	(	png_structrp	png_ptr,
		int	option,
		int	onoff
	)

{
   if (png_ptr != NULL && option >= 0 && option < PNG_OPTION_NEXT &&
      (option & 1) == 0)
   {
      int mask = 3 << option;
      int setting = (2 + (onoff != 0)) << option;
      int current = png_ptr->options;

      png_ptr->options = (png_byte)((current & ~mask) | setting);

      return (current & mask) >> option;
   }

   return PNG_OPTION_INVALID;
}

static int png_image_free_function ( png_voidp  argument )

static

{
   png_imagep image = png_voidcast(png_imagep, argument);
   png_controlp cp = image->opaque;
   png_control c;

   /* Double check that we have a png_ptr - it should be impossible to get here
    * without one.
    */
   if (cp->png_ptr == NULL)
      return 0;

   /* First free any data held in the control structure. */
#  ifdef PNG_STDIO_SUPPORTED
      if (cp->owned_file != 0)
      {
         FILE *fp = png_voidcast(FILE*, cp->png_ptr->io_ptr);
         cp->owned_file = 0;

         /* Ignore errors here. */
         if (fp != NULL)
         {
            cp->png_ptr->io_ptr = NULL;
            (void)fclose(fp);
         }
      }
#  endif

   /* Copy the control structure so that the original, allocated, version can be
    * safely freed.  Notice that a png_error here stops the remainder of the
    * cleanup, but this is probably fine because that would indicate bad memory
    * problems anyway.
    */
   c = *cp;
   image->opaque = &c;
   png_free(c.png_ptr, cp);

   /* Then the structures, calling the correct API. */
   if (c.for_write != 0)
   {
#     ifdef PNG_SIMPLIFIED_WRITE_SUPPORTED
         png_destroy_write_struct(&c.png_ptr, &c.info_ptr);
#     else
         png_error(c.png_ptr, "simplified write not supported");
#     endif
   }
   else
   {
#     ifdef PNG_SIMPLIFIED_READ_SUPPORTED
         png_destroy_read_struct(&c.png_ptr, &c.info_ptr, NULL);
#     else
         png_error(c.png_ptr, "simplified read not supported");
#     endif
   }

   /* Success. */
   return 1;
}

void png_image_free

(

png_imagep

image

)

{
   /* Safely call the real function, but only if doing so is safe at this point
    * (if not inside an error handling context).  Otherwise assume
    * png_safe_execute will call this API after the return.
    */
   if (image != NULL && image->opaque != NULL &&
      image->opaque->error_buf == NULL)
   {
      /* Ignore errors here: */
      (void)png_safe_execute(image, png_image_free_function, image);
      image->opaque = NULL;
   }
}

int png_image_error	(	png_imagep	image,
		png_const_charp	error_message
	)

{
   /* Utility to log an error. */
   png_safecat(image->message, (sizeof image->message), 0, error_message);
   image->warning_or_error |= PNG_IMAGE_ERROR;
   png_image_free(image);
   return 0;
}

Variable Documentation

const png_xy sRGB_xy

static

Initial value:

= 
{
   
    64000, 33000,
    30000, 60000,
    15000,  6000,
    31270, 32900
}

const png_byte D50_nCIEXYZ[12]

static

Initial value:

=
   { 0x00, 0x00, 0xf6, 0xd6, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0xd3, 0x2d }

png_uint_32 adler

png_uint_32 crc

png_uint_32 length

png_uint_32 md5[4]

png_byte have_md5

png_byte is_broken

png_uint_16 intent

const { ... } png_sRGB_checks[]

const png_uint_16 png_sRGB_table[256]

const png_uint_16 png_sRGB_base[512]

const png_byte png_sRGB_delta[512]