/* 
 * 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; 
  } 
} 
