jdhuff.cpp File Reference

#include "jinclude.h"
#include "jpeglib.h"
#include "jdhuff.h"

Include dependency graph for jdhuff.cpp:

Classes
struct	savable_state
struct	huff_entropy_decoder

Macros
#define	JPEG_INTERNALS
#define	ASSIGN_STATE(dest, src)   ((dest) = (src))
#define	MIN_GET_BITS   (BIT_BUF_SIZE-7)
#define	HUFF_EXTEND(x, s)   ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))

Typedefs
typedef huff_entropy_decoder *	huff_entropy_ptr

Functions
static void	start_pass_huff_decoder (j_decompress_ptr cinfo)
void	jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno, d_derived_tbl **pdtbl)
boolean	jpeg_fill_bit_buffer (bitread_working_state *state, register bit_buf_type get_buffer, register int bits_left, int nbits)
int	jpeg_huff_decode (bitread_working_state *state, register bit_buf_type get_buffer, register int bits_left, d_derived_tbl *htbl, int min_bits)
static boolean	process_restart (j_decompress_ptr cinfo)
static boolean	decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
void	jinit_huff_decoder (j_decompress_ptr cinfo)

Variables
static const int	extend_test [16]
static const int	extend_offset [16]

Macro Definition Documentation

#define JPEG_INTERNALS

#define ASSIGN_STATE	(		dest,
			src
	)		((dest) = (src))

#define MIN_GET_BITS   (BIT_BUF_SIZE-7)

#define HUFF_EXTEND	(		x,
			s
	)		((x) < extend_test[s] ? (x) + extend_offset[s] : (x))

Typedef Documentation

typedef huff_entropy_decoder* huff_entropy_ptr

Function Documentation

static void start_pass_huff_decoder ( j_decompress_ptr  cinfo )

static

{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int ci, blkn, dctbl, actbl;
  jpeg_component_info * compptr;

  /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
   * This ought to be an error condition, but we make it a warning because
   * there are some baseline files out there with all zeroes in these bytes.
   */
  if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
      cinfo->Ah != 0 || cinfo->Al != 0)
    WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);

  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
    compptr = cinfo->cur_comp_info[ci];
    dctbl = compptr->dc_tbl_no;
    actbl = compptr->ac_tbl_no;
    /* Compute derived values for Huffman tables */
    /* We may do this more than once for a table, but it's not expensive */
    jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
                & entropy->dc_derived_tbls[dctbl]);
    jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
                & entropy->ac_derived_tbls[actbl]);
    /* Initialize DC predictions to 0 */
    entropy->saved.last_dc_val[ci] = 0;
  }

  /* Precalculate decoding info for each block in an MCU of this scan */
  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
    ci = cinfo->MCU_membership[blkn];
    compptr = cinfo->cur_comp_info[ci];
    /* Precalculate which table to use for each block */
    entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
    entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
    /* Decide whether we really care about the coefficient values */
    if (compptr->component_needed) {
      entropy->dc_needed[blkn] = TRUE;
      /* we don't need the ACs if producing a 1/8th-size image */
      entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1);
    } else {
      entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
    }
  }

  /* Initialize bitread state variables */
  entropy->bitstate.bits_left = 0;
  entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
  entropy->pub.insufficient_data = FALSE;

  /* Initialize restart counter */
  entropy->restarts_to_go = cinfo->restart_interval;
}

void jpeg_make_d_derived_tbl	(	j_decompress_ptr	cinfo,
		boolean	isDC,
		int	tblno,
		d_derived_tbl **	pdtbl
	)

{
  JHUFF_TBL *htbl;
  d_derived_tbl *dtbl;
  int p, i, l, si, numsymbols;
  int lookbits, ctr;
  char huffsize[257];
  unsigned int huffcode[257];
  unsigned int code;

  /* Note that huffsize[] and huffcode[] are filled in code-length order,
   * paralleling the order of the symbols themselves in htbl->huffval[].
   */

  /* Find the input Huffman table */
  if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
  htbl =
    isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
  if (htbl == NULL)
    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);

  /* Allocate a workspace if we haven't already done so. */
  if (*pdtbl == NULL)
    *pdtbl = (d_derived_tbl *)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                  SIZEOF(d_derived_tbl));
  dtbl = *pdtbl;
  dtbl->pub = htbl;     /* fill in back link */
  
  /* Figure C.1: make table of Huffman code length for each symbol */

  p = 0;
  for (l = 1; l <= 16; l++) {
    i = (int) htbl->bits[l];
    if (i < 0 || p + i > 256)   /* protect against table overrun */
      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
    while (i--)
      huffsize[p++] = (char) l;
  }
  huffsize[p] = 0;
  numsymbols = p;
  
  /* Figure C.2: generate the codes themselves */
  /* We also validate that the counts represent a legal Huffman code tree. */
  
  code = 0;
  si = huffsize[0];
  p = 0;
  while (huffsize[p]) {
    while (((int) huffsize[p]) == si) {
      huffcode[p++] = code;
      code++;
    }
    /* code is now 1 more than the last code used for codelength si; but
     * it must still fit in si bits, since no code is allowed to be all ones.
     */
    if (((int32_t) code) >= (((int32_t) 1) << si))
      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
    code <<= 1;
    si++;
  }

  /* Figure F.15: generate decoding tables for bit-sequential decoding */

  p = 0;
  for (l = 1; l <= 16; l++) {
    if (htbl->bits[l]) {
      /* valoffset[l] = huffval[] index of 1st symbol of code length l,
       * minus the minimum code of length l
       */
      dtbl->valoffset[l] = (int32_t) p - (int32_t) huffcode[p];
      p += htbl->bits[l];
      dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
    } else {
      dtbl->maxcode[l] = -1;    /* -1 if no codes of this length */
    }
  }
  dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */

  /* Compute lookahead tables to speed up decoding.
   * First we set all the table entries to 0, indicating "too long";
   * then we iterate through the Huffman codes that are short enough and
   * fill in all the entries that correspond to bit sequences starting
   * with that code.
   */

  MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits));

  p = 0;
  for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
    for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
      /* l = current code's length, p = its index in huffcode[] & huffval[]. */
      /* Generate left-justified code followed by all possible bit sequences */
      lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
      for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
    dtbl->look_nbits[lookbits] = l;
    dtbl->look_sym[lookbits] = htbl->huffval[p];
    lookbits++;
      }
    }
  }

  /* Validate symbols as being reasonable.
   * For AC tables, we make no check, but accept all byte values 0..255.
   * For DC tables, we require the symbols to be in range 0..15.
   * (Tighter bounds could be applied depending on the data depth and mode,
   * but this is sufficient to ensure safe decoding.)
   */
  if (isDC) {
    for (i = 0; i < numsymbols; i++) {
      int sym = htbl->huffval[i];
      if (sym < 0 || sym > 15)
    ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
    }
  }
}

boolean jpeg_fill_bit_buffer	(	bitread_working_state *	state,
		register bit_buf_type	get_buffer,
		register int	bits_left,
		int	nbits
	)

{
  /* Copy heavily used state fields into locals (hopefully registers) */
  register const JOCTET * next_input_byte = state->next_input_byte;
  register size_t bytes_in_buffer = state->bytes_in_buffer;
  j_decompress_ptr cinfo = state->cinfo;

  /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
  /* (It is assumed that no request will be for more than that many bits.) */
  /* We fail to do so only if we hit a marker or are forced to suspend. */

  if (cinfo->unread_marker == 0) {  /* cannot advance past a marker */
    while (bits_left < MIN_GET_BITS) {
      register int c;

      /* Attempt to read a byte */
      if (bytes_in_buffer == 0) {
    if (! (*cinfo->src->fill_input_buffer) (cinfo))
      return FALSE;
    next_input_byte = cinfo->src->next_input_byte;
    bytes_in_buffer = cinfo->src->bytes_in_buffer;
      }
      bytes_in_buffer--;
      c = GETJOCTET(*next_input_byte++);

      /* If it's 0xFF, check and discard stuffed zero byte */
      if (c == 0xFF) {
    /* Loop here to discard any padding FF's on terminating marker,
     * so that we can save a valid unread_marker value.  NOTE: we will
     * accept multiple FF's followed by a 0 as meaning a single FF data
     * byte.  This data pattern is not valid according to the standard.
     */
    do {
      if (bytes_in_buffer == 0) {
        if (! (*cinfo->src->fill_input_buffer) (cinfo))
          return FALSE;
        next_input_byte = cinfo->src->next_input_byte;
        bytes_in_buffer = cinfo->src->bytes_in_buffer;
      }
      bytes_in_buffer--;
      c = GETJOCTET(*next_input_byte++);
    } while (c == 0xFF);

    if (c == 0) {
      /* Found FF/00, which represents an FF data byte */
      c = 0xFF;
    } else {
      /* Oops, it's actually a marker indicating end of compressed data.
       * Save the marker code for later use.
       * Fine point: it might appear that we should save the marker into
       * bitread working state, not straight into permanent state.  But
       * once we have hit a marker, we cannot need to suspend within the
       * current MCU, because we will read no more bytes from the data
       * source.  So it is OK to update permanent state right away.
       */
      cinfo->unread_marker = c;
      /* See if we need to insert some fake zero bits. */
      goto no_more_bytes;
    }
      }

      /* OK, load c into get_buffer */
      get_buffer = (get_buffer << 8) | c;
      bits_left += 8;
    } /* end while */
  } else {
  no_more_bytes:
    /* We get here if we've read the marker that terminates the compressed
     * data segment.  There should be enough bits in the buffer register
     * to satisfy the request; if so, no problem.
     */
    if (nbits > bits_left) {
      /* Uh-oh.  Report corrupted data to user and stuff zeroes into
       * the data stream, so that we can produce some kind of image.
       * We use a nonvolatile flag to ensure that only one warning message
       * appears per data segment.
       */
      if (! cinfo->entropy->insufficient_data) {
    WARNMS(cinfo, JWRN_HIT_MARKER);
    cinfo->entropy->insufficient_data = TRUE;
      }
      /* Fill the buffer with zero bits */
      get_buffer <<= MIN_GET_BITS - bits_left;
      bits_left = MIN_GET_BITS;
    }
  }

  /* Unload the local registers */
  state->next_input_byte = next_input_byte;
  state->bytes_in_buffer = bytes_in_buffer;
  state->get_buffer = get_buffer;
  state->bits_left = bits_left;

  return TRUE;
}

int jpeg_huff_decode	(	bitread_working_state *	state,
		register bit_buf_type	get_buffer,
		register int	bits_left,
		d_derived_tbl *	htbl,
		int	min_bits
	)

{
  register int l = min_bits;
  register int32_t code;

  /* HUFF_DECODE has determined that the code is at least min_bits */
  /* bits long, so fetch that many bits in one swoop. */

  CHECK_BIT_BUFFER(*state, l, return -1);
  code = GET_BITS(l);

  /* Collect the rest of the Huffman code one bit at a time. */
  /* This is per Figure F.16 in the JPEG spec. */

  while (code > htbl->maxcode[l]) {
    code <<= 1;
    CHECK_BIT_BUFFER(*state, 1, return -1);
    code |= GET_BITS(1);
    l++;
  }

  /* Unload the local registers */
  state->get_buffer = get_buffer;
  state->bits_left = bits_left;

  /* With garbage input we may reach the sentinel value l = 17. */

  if (l > 16) {
    WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
    return 0;           /* fake a zero as the safest result */
  }

  return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ];
}

static boolean process_restart ( j_decompress_ptr  cinfo )

static

{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int ci;

  /* Throw away any unused bits remaining in bit buffer; */
  /* include any full bytes in next_marker's count of discarded bytes */
  cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
  entropy->bitstate.bits_left = 0;

  /* Advance past the RSTn marker */
  if (! (*cinfo->marker->read_restart_marker) (cinfo))
    return FALSE;

  /* Re-initialize DC predictions to 0 */
  for (ci = 0; ci < cinfo->comps_in_scan; ci++)
    entropy->saved.last_dc_val[ci] = 0;

  /* Reset restart counter */
  entropy->restarts_to_go = cinfo->restart_interval;

  /* Reset out-of-data flag, unless read_restart_marker left us smack up
   * against a marker.  In that case we will end up treating the next data
   * segment as empty, and we can avoid producing bogus output pixels by
   * leaving the flag set.
   */
  if (cinfo->unread_marker == 0)
    entropy->pub.insufficient_data = FALSE;

  return TRUE;
}

static boolean decode_mcu ( j_decompress_ptr  cinfo, JBLOCKROW *  MCU_data  )

static

{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int blkn;
  BITREAD_STATE_VARS;
  savable_state state;

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
    return FALSE;
  }

  /* If we've run out of data, just leave the MCU set to zeroes.
   * This way, we return uniform gray for the remainder of the segment.
   */
  if (! entropy->pub.insufficient_data) {

    /* Load up working state */
    BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
    ASSIGN_STATE(state, entropy->saved);

    /* Outer loop handles each block in the MCU */

    for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
      JBLOCKROW block = MCU_data[blkn];
      d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
      d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
      register int s, k, r;

      /* Decode a single block's worth of coefficients */

      /* Section F.2.2.1: decode the DC coefficient difference */
      HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
      if (s) {
    CHECK_BIT_BUFFER(br_state, s, return FALSE);
    r = GET_BITS(s);
    s = HUFF_EXTEND(r, s);
      }

      if (entropy->dc_needed[blkn]) {
    /* Convert DC difference to actual value, update last_dc_val */
    int ci = cinfo->MCU_membership[blkn];
    s += state.last_dc_val[ci];
    state.last_dc_val[ci] = s;
    /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
    (*block)[0] = (JCOEF) s;
      }

      if (entropy->ac_needed[blkn]) {

    /* Section F.2.2.2: decode the AC coefficients */
    /* Since zeroes are skipped, output area must be cleared beforehand */
    for (k = 1; k < DCTSIZE2; k++) {
      HUFF_DECODE(s, br_state, actbl, return FALSE, label2);
      
      r = s >> 4;
      s &= 15;
      
      if (s) {
        k += r;
        CHECK_BIT_BUFFER(br_state, s, return FALSE);
        r = GET_BITS(s);
        s = HUFF_EXTEND(r, s);
        /* Output coefficient in natural (dezigzagged) order.
         * Note: the extra entries in jpeg_natural_order[] will save us
         * if k >= DCTSIZE2, which could happen if the data is corrupted.
         */
        (*block)[jpeg_natural_order[k]] = (JCOEF) s;
      } else {
        if (r != 15)
          break;
        k += 15;
      }
    }

      } else {

    /* Section F.2.2.2: decode the AC coefficients */
    /* In this path we just discard the values */
    for (k = 1; k < DCTSIZE2; k++) {
      HUFF_DECODE(s, br_state, actbl, return FALSE, label3);
      
      r = s >> 4;
      s &= 15;
      
      if (s) {
        k += r;
        CHECK_BIT_BUFFER(br_state, s, return FALSE);
        DROP_BITS(s);
      } else {
        if (r != 15)
          break;
        k += 15;
      }
    }

      }
    }

    /* Completed MCU, so update state */
    BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
    ASSIGN_STATE(entropy->saved, state);
  }

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;
}

void jinit_huff_decoder

(

j_decompress_ptr

cinfo

)

{
  huff_entropy_ptr entropy;
  int i;

  entropy = (huff_entropy_ptr)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                SIZEOF(huff_entropy_decoder));
  cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
  entropy->pub.start_pass = start_pass_huff_decoder;
  entropy->pub.decode_mcu = decode_mcu;

  /* Mark tables unallocated */
  for (i = 0; i < NUM_HUFF_TBLS; i++) {
    entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
  }
}

Variable Documentation

const int extend_test[16]

static

Initial value:

=   
  { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
    0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 }

const int extend_offset[16]

static

Initial value:

= 
  { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
    ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
    ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
    ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 }