source: liacs/MIR2010/SourceCode/cximage/jpeg/jdhuff.c@ 422

/*

 * jdhuff.c

 *

 * Copyright (C) 1991-1997, Thomas G. Lane.

 * This file is part of the Independent JPEG Group's software.

 * For conditions of distribution and use, see the accompanying README file.

 *

 * This file contains Huffman entropy decoding routines.

 *

 * Much of the complexity here has to do with supporting input suspension.

 * If the data source module demands suspension, we want to be able to back

 * up to the start of the current MCU.  To do this, we copy state variables

 * into local working storage, and update them back to the permanent

 * storage only upon successful completion of an MCU.

 */



#define JPEG_INTERNALS

#include "jinclude.h"

#include "jpeglib.h"

#include "jdhuff.h"             /* Declarations shared with jdphuff.c */





/*

 * Expanded entropy decoder object for Huffman decoding.

 *

 * The savable_state subrecord contains fields that change within an MCU,

 * but must not be updated permanently until we complete the MCU.

 */



typedef struct {

  int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */

} savable_state;



/* This macro is to work around compilers with missing or broken

 * structure assignment.  You'll need to fix this code if you have

 * such a compiler and you change MAX_COMPS_IN_SCAN.

 */



#ifndef NO_STRUCT_ASSIGN

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

#else

#if MAX_COMPS_IN_SCAN == 4

#define ASSIGN_STATE(dest,src)  \

        ((dest).last_dc_val[0] = (src).last_dc_val[0], \

         (dest).last_dc_val[1] = (src).last_dc_val[1], \

         (dest).last_dc_val[2] = (src).last_dc_val[2], \

         (dest).last_dc_val[3] = (src).last_dc_val[3])

#endif

#endif





typedef struct {

  struct jpeg_entropy_decoder pub; /* public fields */



  /* These fields are loaded into local variables at start of each MCU.

   * In case of suspension, we exit WITHOUT updating them.

   */

  bitread_perm_state bitstate;  /* Bit buffer at start of MCU */

  savable_state saved;          /* Other state at start of MCU */



  /* These fields are NOT loaded into local working state. */

  unsigned int restarts_to_go;  /* MCUs left in this restart interval */



  /* Pointers to derived tables (these workspaces have image lifespan) */

  d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];

  d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];



  /* Precalculated info set up by start_pass for use in decode_mcu: */



  /* Pointers to derived tables to be used for each block within an MCU */

  d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];

  d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];

  /* Whether we care about the DC and AC coefficient values for each block */

  boolean dc_needed[D_MAX_BLOCKS_IN_MCU];

  boolean ac_needed[D_MAX_BLOCKS_IN_MCU];

} huff_entropy_decoder;



typedef huff_entropy_decoder * huff_entropy_ptr;





/*

 * Initialize for a Huffman-compressed scan.

 */



METHODDEF(void)

start_pass_huff_decoder (j_decompress_ptr cinfo)

{

  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;

}





/*

 * Compute the derived values for a Huffman table.

 * This routine also performs some validation checks on the table.

 *

 * Note this is also used by jdphuff.c.

 */



GLOBAL(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) 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);

    }

  }

}





/*

 * Out-of-line code for bit fetching (shared with jdphuff.c).

 * See jdhuff.h for info about usage.

 * Note: current values of get_buffer and bits_left are passed as parameters,

 * but are returned in the corresponding fields of the state struct.

 *

 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width

 * of get_buffer to be used.  (On machines with wider words, an even larger

 * buffer could be used.)  However, on some machines 32-bit shifts are

 * quite slow and take time proportional to the number of places shifted.

 * (This is true with most PC compilers, for instance.)  In this case it may

 * be a win to set MIN_GET_BITS to the minimum value of 15.  This reduces the

 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.

 */



#ifdef SLOW_SHIFT_32

#define MIN_GET_BITS  15        /* minimum allowable value */

#else

#define MIN_GET_BITS  (BIT_BUF_SIZE-7)

#endif





GLOBAL(boolean)

jpeg_fill_bit_buffer (bitread_working_state * state,

                      register bit_buf_type get_buffer, register int bits_left,

                      int nbits)

/* Load up the bit buffer to a depth of at least 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;

}





/*

 * Out-of-line code for Huffman code decoding.

 * See jdhuff.h for info about usage.

 */



GLOBAL(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 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]) ];

}





/*

 * Figure F.12: extend sign bit.

 * On some machines, a shift and add will be faster than a table lookup.

 */



#ifdef AVOID_TABLES



#define HUFF_EXTEND(x,s)  ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))



#else



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



static const int extend_test[16] =   /* entry n is 2**(n-1) */

  { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,

    0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };



static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */

  { 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 };



#endif /* AVOID_TABLES */





/*

 * Check for a restart marker & resynchronize decoder.

 * Returns FALSE if must suspend.

 */



LOCAL(boolean)

process_restart (j_decompress_ptr cinfo)

{

  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;

}





/*

 * Decode and return one MCU's worth of Huffman-compressed coefficients.

 * The coefficients are reordered from zigzag order into natural array order,

 * but are not dequantized.

 *

 * The i'th block of the MCU is stored into the block pointed to by

 * MCU_data[i].  WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.

 * (Wholesale zeroing is usually a little faster than retail...)

 *

 * Returns FALSE if data source requested suspension.  In that case no

 * changes have been made to permanent state.  (Exception: some output

 * coefficients may already have been assigned.  This is harmless for

 * this module, since we'll just re-assign them on the next call.)

 */



METHODDEF(boolean)

decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)

{

  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;

}





/*

 * Module initialization routine for Huffman entropy decoding.

 */



GLOBAL(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;

  }

}

/*

 * BEWARE OF KLUDGE:  This subroutine is a hack for decoding illegal JPEG-in-

 *                    TIFF encapsulations produced by Microsoft's Wang Imaging

 * for Windows application with the public-domain TIFF Library.  Based upon an

 * examination of selected output files, this program apparently divides a JPEG

 * bit-stream into consecutive horizontal TIFF "strips", such that the JPEG

 * encoder's/decoder's DC coefficients for each image component are reset before

 * each "strip".  Moreover, a "strip" is not necessarily encoded in a multiple

 * of 8 bits, so one must sometimes discard 1-7 bits at the end of each "strip"

 * for alignment to the next input-Byte storage boundary.  IJG JPEG Library

 * decoder state is not normally exposed to client applications, so this sub-

 * routine provides the TIFF Library with a "hook" to make these corrections.

 * It should be called after "jpeg_start_decompress()" and before

 * "jpeg_finish_decompress()", just before decoding each "strip" using

 * "jpeg_read_raw_data()" or "jpeg_read_scanlines()".

 *

 * This kludge is not sanctioned or supported by the Independent JPEG Group, and

 * future changes to the IJG JPEG Library might invalidate it.  Do not send bug

 * reports about this code to IJG developers.  Instead, contact the author for

 * advice: Scott B. Marovich <marovich@hpl.hp.com>, Hewlett-Packard Labs, 6/01.

 */

GLOBAL(void)

jpeg_reset_huff_decode (register j_decompress_ptr cinfo,register float *refbw)

{ register huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;

  register int ci = 0;



  /* Re-initialize DC predictions */

  do entropy->saved.last_dc_val[ci] = (int)-refbw[ci << 1];

  while (++ci < cinfo->comps_in_scan);

  /* Discard encoded input bits, up to the next Byte boundary */

  entropy->bitstate.bits_left &= ~7;

}