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plt-scheme  4.2.1
Classes | Defines | Typedefs | Functions | Variables
jdhuff.c File Reference
#include "jinclude.h"
#include "jpeglib.h"
#include "jdhuff.h"

Go to the source code of this file.

Classes

struct  savable_state
struct  huff_entropy_decoder

Defines

#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_decoderhuff_entropy_ptr

Functions

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

Variables

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

Class Documentation

struct savable_state

Definition at line 29 of file jchuff.c.

Class Members
unsigned int EOBRUN
int last_dc_val
int put_bits
INT32 put_buffer
struct huff_entropy_decoder

Definition at line 52 of file jdhuff.c.

Collaboration diagram for huff_entropy_decoder:
Class Members
d_derived_tbl * ac_cur_tbls
d_derived_tbl * ac_derived_tbls
boolean ac_needed
bitread_perm_state bitstate
d_derived_tbl * dc_cur_tbls
d_derived_tbl * dc_derived_tbls
boolean dc_needed
unsigned int restarts_to_go
savable_state saved

Define Documentation

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

Definition at line 40 of file jdhuff.c.

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

Definition at line 447 of file jdhuff.c.

#define JPEG_INTERNALS

Definition at line 17 of file jdhuff.c.

#define MIN_GET_BITS   (BIT_BUF_SIZE-7)

Definition at line 287 of file jdhuff.c.


Typedef Documentation

Definition at line 78 of file jdhuff.c.


Function Documentation

decode_mcu ( j_decompress_ptr  cinfo,
JBLOCKROW MCU_data 
)

Definition at line 517 of file jdhuff.c.

{
  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;
}

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Definition at line 635 of file jdhuff.c.

{
  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;
  }
}

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

Definition at line 292 of file jdhuff.c.

{
  /* 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;
}
jpeg_huff_decode ( bitread_working_state state,
register bit_buf_type  get_buffer,
register int  bits_left,
d_derived_tbl htbl,
int  min_bits 
)

Definition at line 398 of file jdhuff.c.

{
  register int l = min_bits;
  register INT32 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]) ];
}
jpeg_make_d_derived_tbl ( j_decompress_ptr  cinfo,
boolean  isDC,
int  tblno,
d_derived_tbl **  pdtbl 
)

Definition at line 149 of file jdhuff.c.

{
  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) code) >= (((INT32) 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) p - (INT32) 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);
    }
  }
}

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Definition at line 468 of file jdhuff.c.

{
  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;
}

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Definition at line 86 of file jdhuff.c.

{
  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;
}

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Variable Documentation

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 }

Definition at line 453 of file jdhuff.c.

const int extend_test[16] [static]
Initial value:
   
  { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
    0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 }

Definition at line 449 of file jdhuff.c.