/*+
−
 * 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,+
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 * but are not dequantized.+
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 *+
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 * The i'th block of the MCU is stored into the block pointed to by+
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 * MCU_data[i].  WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.+
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 * (Wholesale zeroing is usually a little faster than retail...)+
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 *+
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 * Returns FALSE if data source requested suspension.  In that case no+
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 * changes have been made to permanent state.  (Exception: some output+
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 * 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;+
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  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.+
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   * 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];+
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      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;+
−
  }+
−
}+
−