www.pudn.com > imgport.rar > jchuff.c, change:2008-11-05,size:29161b


/* 
 * jchuff.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 encoding routines. 
 * 
 * Much of the complexity here has to do with supporting output suspension. 
 * If the data destination 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 JPEG objects only upon successful completion of an MCU. 
 */ 
 
#define JPEG_INTERNALS 
#include "jinclude.h" 
#include "jpeglib.h" 
#include "jchuff.h"		/* Declarations shared with jcphuff.c */ 
 
 
/* Expanded entropy encoder object for Huffman encoding. 
 * 
 * The savable_state subrecord contains fields that change within an MCU, 
 * but must not be updated permanently until we complete the MCU. 
 */ 
 
typedef struct { 
  JPEG_INT32 put_buffer;		/* current bit-accumulation buffer */ 
  int put_bits;			/* # of bits now in it */ 
  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).put_buffer = (src).put_buffer, \ 
	 (dest).put_bits = (src).put_bits, \ 
	 (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_encoder pub; /* public fields */ 
 
  savable_state saved;		/* Bit buffer & DC 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 */ 
  int next_restart_num;		/* next restart number to write (0-7) */ 
 
  /* Pointers to derived tables (these workspaces have image lifespan) */ 
  c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS]; 
  c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS]; 
 
#ifdef ENTROPY_OPT_SUPPORTED	/* Statistics tables for optimization */ 
  long * dc_count_ptrs[NUM_HUFF_TBLS]; 
  long * ac_count_ptrs[NUM_HUFF_TBLS]; 
#endif 
} huff_entropy_encoder; 
 
typedef huff_entropy_encoder * huff_entropy_ptr; 
 
/* Working state while writing an MCU. 
 * This struct contains all the fields that are needed by subroutines. 
 */ 
 
typedef struct { 
  JOCTET * next_output_byte;	/* => next byte to write in buffer */ 
  size_t free_in_buffer;	/* # of byte spaces remaining in buffer */ 
  savable_state cur;		/* Current bit buffer & DC state */ 
  j_compress_ptr cinfo;		/* dump_buffer needs access to this */ 
} working_state; 
 
 
/* Forward declarations */ 
METHODDEF(boolean) encode_mcu_huff JPP((j_compress_ptr cinfo, 
					JBLOCKROW *MCU_data)); 
METHODDEF(void) finish_pass_huff JPP((j_compress_ptr cinfo)); 
#ifdef ENTROPY_OPT_SUPPORTED 
METHODDEF(boolean) encode_mcu_gather JPP((j_compress_ptr cinfo, 
					  JBLOCKROW *MCU_data)); 
METHODDEF(void) finish_pass_gather JPP((j_compress_ptr cinfo)); 
#endif 
 
 
/* 
 * Initialize for a Huffman-compressed scan. 
 * If gather_statistics is TRUE, we do not output anything during the scan, 
 * just count the Huffman symbols used and generate Huffman code tables. 
 */ 
 
METHODDEF(void) 
start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics) 
{ 
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 
  int ci, dctbl, actbl; 
  jpeg_component_info * compptr; 
 
  if (gather_statistics) { 
#ifdef ENTROPY_OPT_SUPPORTED 
    entropy->pub.encode_mcu = encode_mcu_gather; 
    entropy->pub.finish_pass = finish_pass_gather; 
#else 
    ERREXIT(cinfo, JERR_NOT_COMPILED); 
#endif 
  } else { 
    entropy->pub.encode_mcu = encode_mcu_huff; 
    entropy->pub.finish_pass = finish_pass_huff; 
  } 
 
  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; 
    if (gather_statistics) { 
#ifdef ENTROPY_OPT_SUPPORTED 
      /* Check for invalid table indexes */ 
      /* (make_c_derived_tbl does this in the other path) */ 
      if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS) 
	ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl); 
      if (actbl < 0 || actbl >= NUM_HUFF_TBLS) 
	ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl); 
      /* Allocate and zero the statistics tables */ 
      /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */ 
      if (entropy->dc_count_ptrs[dctbl] == NULL) 
	entropy->dc_count_ptrs[dctbl] = (long *) 
	  (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 
				      257 * SIZEOF(long)); 
      MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * SIZEOF(long)); 
      if (entropy->ac_count_ptrs[actbl] == NULL) 
	entropy->ac_count_ptrs[actbl] = (long *) 
	  (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 
				      257 * SIZEOF(long)); 
      MEMZERO(entropy->ac_count_ptrs[actbl], 257 * SIZEOF(long)); 
#endif 
    } else { 
      /* Compute derived values for Huffman tables */ 
      /* We may do this more than once for a table, but it's not expensive */ 
      jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl, 
			      & entropy->dc_derived_tbls[dctbl]); 
      jpeg_make_c_derived_tbl(cinfo, FALSE, actbl, 
			      & entropy->ac_derived_tbls[actbl]); 
    } 
    /* Initialize DC predictions to 0 */ 
    entropy->saved.last_dc_val[ci] = 0; 
  } 
 
  /* Initialize bit buffer to empty */ 
  entropy->saved.put_buffer = 0; 
  entropy->saved.put_bits = 0; 
 
  /* Initialize restart stuff */ 
  entropy->restarts_to_go = cinfo->restart_interval; 
  entropy->next_restart_num = 0; 
} 
 
 
/* 
 * Compute the derived values for a Huffman table. 
 * This routine also performs some validation checks on the table. 
 * 
 * Note this is also used by jcphuff.c. 
 */ 
 
GLOBAL(void) 
jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno, 
			 c_derived_tbl ** pdtbl) 
{ 
  JHUFF_TBL *htbl; 
  c_derived_tbl *dtbl; 
  int p, i, l, lastp, si, maxsymbol; 
  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 = (c_derived_tbl *) 
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 
				  SIZEOF(c_derived_tbl)); 
  dtbl = *pdtbl; 
   
  /* 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; 
  lastp = 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 (((JPEG_INT32) code) >= (((JPEG_INT32) 1) << si)) 
      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 
    code <<= 1; 
    si++; 
  } 
   
  /* Figure C.3: generate encoding tables */ 
  /* These are code and size indexed by symbol value */ 
 
  /* Set all codeless symbols to have code length 0; 
   * this lets us detect duplicate VAL entries here, and later 
   * allows emit_bits to detect any attempt to emit such symbols. 
   */ 
  MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi)); 
 
  /* This is also a convenient place to check for out-of-range 
   * and duplicated VAL entries.  We allow 0..255 for AC symbols 
   * but only 0..15 for DC.  (We could constrain them further 
   * based on data depth and mode, but this seems enough.) 
   */ 
  maxsymbol = isDC ? 15 : 255; 
 
  for (p = 0; p < lastp; p++) { 
    i = htbl->huffval[p]; 
    if (i < 0 || i > maxsymbol || dtbl->ehufsi[i]) 
      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 
    dtbl->ehufco[i] = huffcode[p]; 
    dtbl->ehufsi[i] = huffsize[p]; 
  } 
} 
 
 
/* Outputting bytes to the file */ 
 
/* Emit a byte, taking 'action' if must suspend. */ 
#define emit_byte(state,val,action)  \ 
	{ *(state)->next_output_byte++ = (JOCTET) (val);  \ 
	  if (--(state)->free_in_buffer == 0)  \ 
	    if (! dump_buffer(state))  \ 
	      { action; } } 
 
 
LOCAL(boolean) 
dump_buffer (working_state * state) 
/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */ 
{ 
  struct jpeg_destination_mgr * dest = state->cinfo->dest; 
 
  if (! (*dest->empty_output_buffer) (state->cinfo)) 
    return FALSE; 
  /* After a successful buffer dump, must reset buffer pointers */ 
  state->next_output_byte = dest->next_output_byte; 
  state->free_in_buffer = dest->free_in_buffer; 
  return TRUE; 
} 
 
 
/* Outputting bits to the file */ 
 
/* Only the right 24 bits of put_buffer are used; the valid bits are 
 * left-justified in this part.  At most 16 bits can be passed to emit_bits 
 * in one call, and we never retain more than 7 bits in put_buffer 
 * between calls, so 24 bits are sufficient. 
 */ 
 
INLINE 
LOCAL(boolean) 
emit_bits (working_state * state, unsigned int code, int size) 
/* Emit some bits; return TRUE if successful, FALSE if must suspend */ 
{ 
  /* This routine is heavily used, so it's worth coding tightly. */ 
  register JPEG_INT32 put_buffer = (JPEG_INT32) code; 
  register int put_bits = state->cur.put_bits; 
 
  /* if size is 0, caller used an invalid Huffman table entry */ 
  if (size == 0) 
    ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE); 
 
  put_buffer &= (((JPEG_INT32) 1)<<size) - 1; /* mask off any extra bits in code */ 
   
  put_bits += size;		/* new number of bits in buffer */ 
   
  put_buffer <<= 24 - put_bits; /* align incoming bits */ 
 
  put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */ 
   
  while (put_bits >= 8) { 
    int c = (int) ((put_buffer >> 16) & 0xFF); 
     
    emit_byte(state, c, return FALSE); 
    if (c == 0xFF) {		/* need to stuff a zero byte? */ 
      emit_byte(state, 0, return FALSE); 
    } 
    put_buffer <<= 8; 
    put_bits -= 8; 
  } 
 
  state->cur.put_buffer = put_buffer; /* update state variables */ 
  state->cur.put_bits = put_bits; 
 
  return TRUE; 
} 
 
 
LOCAL(boolean) 
flush_bits (working_state * state) 
{ 
  if (! emit_bits(state, 0x7F, 7)) /* fill any partial byte with ones */ 
    return FALSE; 
  state->cur.put_buffer = 0;	/* and reset bit-buffer to empty */ 
  state->cur.put_bits = 0; 
  return TRUE; 
} 
 
 
/* Encode a single block's worth of coefficients */ 
 
LOCAL(boolean) 
encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val, 
		  c_derived_tbl *dctbl, c_derived_tbl *actbl) 
{ 
  register int temp, temp2; 
  register int nbits; 
  register int k, r, i; 
   
  /* Encode the DC coefficient difference per section F.1.2.1 */ 
   
  temp = temp2 = block[0] - last_dc_val; 
 
  if (temp < 0) { 
    temp = -temp;		/* temp is abs value of input */ 
    /* For a negative input, want temp2 = bitwise complement of abs(input) */ 
    /* This code assumes we are on a two's complement machine */ 
    temp2--; 
  } 
   
  /* Find the number of bits needed for the magnitude of the coefficient */ 
  nbits = 0; 
  while (temp) { 
    nbits++; 
    temp >>= 1; 
  } 
  /* Check for out-of-range coefficient values. 
   * Since we're encoding a difference, the range limit is twice as much. 
   */ 
  if (nbits > MAX_COEF_BITS+1) 
    ERREXIT(state->cinfo, JERR_BAD_DCT_COEF); 
   
  /* Emit the Huffman-coded symbol for the number of bits */ 
  if (! emit_bits(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits])) 
    return FALSE; 
 
  /* Emit that number of bits of the value, if positive, */ 
  /* or the complement of its magnitude, if negative. */ 
  if (nbits)			/* emit_bits rejects calls with size 0 */ 
    if (! emit_bits(state, (unsigned int) temp2, nbits)) 
      return FALSE; 
 
  /* Encode the AC coefficients per section F.1.2.2 */ 
   
  r = 0;			/* r = run length of zeros */ 
   
  for (k = 1; k < DCTSIZE2; k++) { 
    if ((temp = block[jpeg_natural_order[k]]) == 0) { 
      r++; 
    } else { 
      /* if run length > 15, must emit special run-length-16 codes (0xF0) */ 
      while (r > 15) { 
	if (! emit_bits(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0])) 
	  return FALSE; 
	r -= 16; 
      } 
 
      temp2 = temp; 
      if (temp < 0) { 
	temp = -temp;		/* temp is abs value of input */ 
	/* This code assumes we are on a two's complement machine */ 
	temp2--; 
      } 
       
      /* Find the number of bits needed for the magnitude of the coefficient */ 
      nbits = 1;		/* there must be at least one 1 bit */ 
      while ((temp >>= 1)) 
	nbits++; 
      /* Check for out-of-range coefficient values */ 
      if (nbits > MAX_COEF_BITS) 
	ERREXIT(state->cinfo, JERR_BAD_DCT_COEF); 
       
      /* Emit Huffman symbol for run length / number of bits */ 
      i = (r << 4) + nbits; 
      if (! emit_bits(state, actbl->ehufco[i], actbl->ehufsi[i])) 
	return FALSE; 
 
      /* Emit that number of bits of the value, if positive, */ 
      /* or the complement of its magnitude, if negative. */ 
      if (! emit_bits(state, (unsigned int) temp2, nbits)) 
	return FALSE; 
       
      r = 0; 
    } 
  } 
 
  /* If the last coef(s) were zero, emit an end-of-block code */ 
  if (r > 0) 
    if (! emit_bits(state, actbl->ehufco[0], actbl->ehufsi[0])) 
      return FALSE; 
 
  return TRUE; 
} 
 
 
/* 
 * Emit a restart marker & resynchronize predictions. 
 */ 
 
LOCAL(boolean) 
emit_restart (working_state * state, int restart_num) 
{ 
  int ci; 
 
  if (! flush_bits(state)) 
    return FALSE; 
 
  emit_byte(state, 0xFF, return FALSE); 
  emit_byte(state, JPEG_RST0 + restart_num, return FALSE); 
 
  /* Re-initialize DC predictions to 0 */ 
  for (ci = 0; ci < state->cinfo->comps_in_scan; ci++) 
    state->cur.last_dc_val[ci] = 0; 
 
  /* The restart counter is not updated until we successfully write the MCU. */ 
 
  return TRUE; 
} 
 
 
/* 
 * Encode and output one MCU's worth of Huffman-compressed coefficients. 
 */ 
 
METHODDEF(boolean) 
encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 
{ 
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 
  working_state state; 
  int blkn, ci; 
  jpeg_component_info * compptr; 
 
  /* Load up working state */ 
  state.next_output_byte = cinfo->dest->next_output_byte; 
  state.free_in_buffer = cinfo->dest->free_in_buffer; 
  ASSIGN_STATE(state.cur, entropy->saved); 
  state.cinfo = cinfo; 
 
  /* Emit restart marker if needed */ 
  if (cinfo->restart_interval) { 
    if (entropy->restarts_to_go == 0) 
      if (! emit_restart(&state, entropy->next_restart_num)) 
	return FALSE; 
  } 
 
  /* Encode the MCU data blocks */ 
  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 
    ci = cinfo->MCU_membership[blkn]; 
    compptr = cinfo->cur_comp_info[ci]; 
    if (! encode_one_block(&state, 
			   MCU_data[blkn][0], state.cur.last_dc_val[ci], 
			   entropy->dc_derived_tbls[compptr->dc_tbl_no], 
			   entropy->ac_derived_tbls[compptr->ac_tbl_no])) 
      return FALSE; 
    /* Update last_dc_val */ 
    state.cur.last_dc_val[ci] = MCU_data[blkn][0][0]; 
  } 
 
  /* Completed MCU, so update state */ 
  cinfo->dest->next_output_byte = state.next_output_byte; 
  cinfo->dest->free_in_buffer = state.free_in_buffer; 
  ASSIGN_STATE(entropy->saved, state.cur); 
 
  /* Update restart-interval state too */ 
  if (cinfo->restart_interval) { 
    if (entropy->restarts_to_go == 0) { 
      entropy->restarts_to_go = cinfo->restart_interval; 
      entropy->next_restart_num++; 
      entropy->next_restart_num &= 7; 
    } 
    entropy->restarts_to_go--; 
  } 
 
  return TRUE; 
} 
 
 
/* 
 * Finish up at the end of a Huffman-compressed scan. 
 */ 
 
METHODDEF(void) 
finish_pass_huff (j_compress_ptr cinfo) 
{ 
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 
  working_state state; 
 
  /* Load up working state ... flush_bits needs it */ 
  state.next_output_byte = cinfo->dest->next_output_byte; 
  state.free_in_buffer = cinfo->dest->free_in_buffer; 
  ASSIGN_STATE(state.cur, entropy->saved); 
  state.cinfo = cinfo; 
 
  /* Flush out the last data */ 
  if (! flush_bits(&state)) 
    ERREXIT(cinfo, JERR_CANT_SUSPEND); 
 
  /* Update state */ 
  cinfo->dest->next_output_byte = state.next_output_byte; 
  cinfo->dest->free_in_buffer = state.free_in_buffer; 
  ASSIGN_STATE(entropy->saved, state.cur); 
} 
 
 
/* 
 * Huffman coding optimization. 
 * 
 * We first scan the supplied data and count the number of uses of each symbol 
 * that is to be Huffman-coded. (This process MUST agree with the code above.) 
 * Then we build a Huffman coding tree for the observed counts. 
 * Symbols which are not needed at all for the particular image are not 
 * assigned any code, which saves space in the DHT marker as well as in 
 * the compressed data. 
 */ 
 
#ifdef ENTROPY_OPT_SUPPORTED 
 
 
/* Process a single block's worth of coefficients */ 
 
LOCAL(void) 
htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val, 
		 long dc_counts[], long ac_counts[]) 
{ 
  register int temp; 
  register int nbits; 
  register int k, r; 
   
  /* Encode the DC coefficient difference per section F.1.2.1 */ 
   
  temp = block[0] - last_dc_val; 
  if (temp < 0) 
    temp = -temp; 
   
  /* Find the number of bits needed for the magnitude of the coefficient */ 
  nbits = 0; 
  while (temp) { 
    nbits++; 
    temp >>= 1; 
  } 
  /* Check for out-of-range coefficient values. 
   * Since we're encoding a difference, the range limit is twice as much. 
   */ 
  if (nbits > MAX_COEF_BITS+1) 
    ERREXIT(cinfo, JERR_BAD_DCT_COEF); 
 
  /* Count the Huffman symbol for the number of bits */ 
  dc_counts[nbits]++; 
   
  /* Encode the AC coefficients per section F.1.2.2 */ 
   
  r = 0;			/* r = run length of zeros */ 
   
  for (k = 1; k < DCTSIZE2; k++) { 
    if ((temp = block[jpeg_natural_order[k]]) == 0) { 
      r++; 
    } else { 
      /* if run length > 15, must emit special run-length-16 codes (0xF0) */ 
      while (r > 15) { 
	ac_counts[0xF0]++; 
	r -= 16; 
      } 
       
      /* Find the number of bits needed for the magnitude of the coefficient */ 
      if (temp < 0) 
	temp = -temp; 
       
      /* Find the number of bits needed for the magnitude of the coefficient */ 
      nbits = 1;		/* there must be at least one 1 bit */ 
      while ((temp >>= 1)) 
	nbits++; 
      /* Check for out-of-range coefficient values */ 
      if (nbits > MAX_COEF_BITS) 
	ERREXIT(cinfo, JERR_BAD_DCT_COEF); 
       
      /* Count Huffman symbol for run length / number of bits */ 
      ac_counts[(r << 4) + nbits]++; 
       
      r = 0; 
    } 
  } 
 
  /* If the last coef(s) were zero, emit an end-of-block code */ 
  if (r > 0) 
    ac_counts[0]++; 
} 
 
 
/* 
 * Trial-encode one MCU's worth of Huffman-compressed coefficients. 
 * No data is actually output, so no suspension return is possible. 
 */ 
 
METHODDEF(boolean) 
encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 
{ 
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 
  int blkn, ci; 
  jpeg_component_info * compptr; 
 
  /* Take care of restart intervals if needed */ 
  if (cinfo->restart_interval) { 
    if (entropy->restarts_to_go == 0) { 
      /* Re-initialize DC predictions to 0 */ 
      for (ci = 0; ci < cinfo->comps_in_scan; ci++) 
	entropy->saved.last_dc_val[ci] = 0; 
      /* Update restart state */ 
      entropy->restarts_to_go = cinfo->restart_interval; 
    } 
    entropy->restarts_to_go--; 
  } 
 
  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 
    ci = cinfo->MCU_membership[blkn]; 
    compptr = cinfo->cur_comp_info[ci]; 
    htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci], 
		    entropy->dc_count_ptrs[compptr->dc_tbl_no], 
		    entropy->ac_count_ptrs[compptr->ac_tbl_no]); 
    entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0]; 
  } 
 
  return TRUE; 
} 
 
 
/* 
 * Generate the best Huffman code table for the given counts, fill htbl. 
 * Note this is also used by jcphuff.c. 
 * 
 * The JPEG standard requires that no symbol be assigned a codeword of all 
 * one bits (so that padding bits added at the end of a compressed segment 
 * can't look like a valid code).  Because of the canonical ordering of 
 * codewords, this just means that there must be an unused slot in the 
 * longest codeword length category.  Section K.2 of the JPEG spec suggests 
 * reserving such a slot by pretending that symbol 256 is a valid symbol 
 * with count 1.  In theory that's not optimal; giving it count zero but 
 * including it in the symbol set anyway should give a better Huffman code. 
 * But the theoretically better code actually seems to come out worse in 
 * practice, because it produces more all-ones bytes (which incur stuffed 
 * zero bytes in the final file).  In any case the difference is tiny. 
 * 
 * The JPEG standard requires Huffman codes to be no more than 16 bits long. 
 * If some symbols have a very small but nonzero probability, the Huffman tree 
 * must be adjusted to meet the code length restriction.  We currently use 
 * the adjustment method suggested in JPEG section K.2.  This method is *not* 
 * optimal; it may not choose the best possible limited-length code.  But 
 * typically only very-low-frequency symbols will be given less-than-optimal 
 * lengths, so the code is almost optimal.  Experimental comparisons against 
 * an optimal limited-length-code algorithm indicate that the difference is 
 * microscopic --- usually less than a hundredth of a percent of total size. 
 * So the extra complexity of an optimal algorithm doesn't seem worthwhile. 
 */ 
 
GLOBAL(void) 
jpeg_gen_optimal_table (j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[]) 
{ 
#define MAX_CLEN 32		/* assumed maximum initial code length */ 
  UINT8 bits[MAX_CLEN+1];	/* bits[k] = # of symbols with code length k */ 
  int codesize[257];		/* codesize[k] = code length of symbol k */ 
  int others[257];		/* next symbol in current branch of tree */ 
  int c1, c2; 
  int p, i, j; 
  long v; 
 
  /* This algorithm is explained in section K.2 of the JPEG standard */ 
 
  MEMZERO(bits, SIZEOF(bits)); 
  MEMZERO(codesize, SIZEOF(codesize)); 
  for (i = 0; i < 257; i++) 
    others[i] = -1;		/* init links to empty */ 
   
  freq[256] = 1;		/* make sure 256 has a nonzero count */ 
  /* Including the pseudo-symbol 256 in the Huffman procedure guarantees 
   * that no real symbol is given code-value of all ones, because 256 
   * will be placed last in the largest codeword category. 
   */ 
 
  /* Huffman's basic algorithm to assign optimal code lengths to symbols */ 
 
  for (;;) { 
    /* Find the smallest nonzero frequency, set c1 = its symbol */ 
    /* In case of ties, take the larger symbol number */ 
    c1 = -1; 
    v = 1000000000L; 
    for (i = 0; i <= 256; i++) { 
      if (freq[i] && freq[i] <= v) { 
	v = freq[i]; 
	c1 = i; 
      } 
    } 
 
    /* Find the next smallest nonzero frequency, set c2 = its symbol */ 
    /* In case of ties, take the larger symbol number */ 
    c2 = -1; 
    v = 1000000000L; 
    for (i = 0; i <= 256; i++) { 
      if (freq[i] && freq[i] <= v && i != c1) { 
	v = freq[i]; 
	c2 = i; 
      } 
    } 
 
    /* Done if we've merged everything into one frequency */ 
    if (c2 < 0) 
      break; 
     
    /* Else merge the two counts/trees */ 
    freq[c1] += freq[c2]; 
    freq[c2] = 0; 
 
    /* Increment the codesize of everything in c1's tree branch */ 
    codesize[c1]++; 
    while (others[c1] >= 0) { 
      c1 = others[c1]; 
      codesize[c1]++; 
    } 
     
    others[c1] = c2;		/* chain c2 onto c1's tree branch */ 
     
    /* Increment the codesize of everything in c2's tree branch */ 
    codesize[c2]++; 
    while (others[c2] >= 0) { 
      c2 = others[c2]; 
      codesize[c2]++; 
    } 
  } 
 
  /* Now count the number of symbols of each code length */ 
  for (i = 0; i <= 256; i++) { 
    if (codesize[i]) { 
      /* The JPEG standard seems to think that this can't happen, */ 
      /* but I'm paranoid... */ 
      if (codesize[i] > MAX_CLEN) 
	ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW); 
 
      bits[codesize[i]]++; 
    } 
  } 
 
  /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure 
   * Huffman procedure assigned any such lengths, we must adjust the coding. 
   * Here is what the JPEG spec says about how this next bit works: 
   * Since symbols are paired for the longest Huffman code, the symbols are 
   * removed from this length category two at a time.  The prefix for the pair 
   * (which is one bit shorter) is allocated to one of the pair; then, 
   * skipping the BITS entry for that prefix length, a code word from the next 
   * shortest nonzero BITS entry is converted into a prefix for two code words 
   * one bit longer. 
   */ 
   
  for (i = MAX_CLEN; i > 16; i--) { 
    while (bits[i] > 0) { 
      j = i - 2;		/* find length of new prefix to be used */ 
      while (bits[j] == 0) 
	j--; 
       
      bits[i] -= 2;		/* remove two symbols */ 
      bits[i-1]++;		/* one goes in this length */ 
      bits[j+1] += 2;		/* two new symbols in this length */ 
      bits[j]--;		/* symbol of this length is now a prefix */ 
    } 
  } 
 
  /* Remove the count for the pseudo-symbol 256 from the largest codelength */ 
  while (bits[i] == 0)		/* find largest codelength still in use */ 
    i--; 
  bits[i]--; 
   
  /* Return final symbol counts (only for lengths 0..16) */ 
  MEMCOPY(htbl->bits, bits, SIZEOF(htbl->bits)); 
   
  /* Return a list of the symbols sorted by code length */ 
  /* It's not real clear to me why we don't need to consider the codelength 
   * changes made above, but the JPEG spec seems to think this works. 
   */ 
  p = 0; 
  for (i = 1; i <= MAX_CLEN; i++) { 
    for (j = 0; j <= 255; j++) { 
      if (codesize[j] == i) { 
	htbl->huffval[p] = (UINT8) j; 
	p++; 
      } 
    } 
  } 
 
  /* Set sent_table FALSE so updated table will be written to JPEG file. */ 
  htbl->sent_table = FALSE; 
} 
 
 
/* 
 * Finish up a statistics-gathering pass and create the new Huffman tables. 
 */ 
 
METHODDEF(void) 
finish_pass_gather (j_compress_ptr cinfo) 
{ 
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 
  int ci, dctbl, actbl; 
  jpeg_component_info * compptr; 
  JHUFF_TBL **htblptr; 
  boolean did_dc[NUM_HUFF_TBLS]; 
  boolean did_ac[NUM_HUFF_TBLS]; 
 
  /* It's important not to apply jpeg_gen_optimal_table more than once 
   * per table, because it clobbers the input frequency counts! 
   */ 
  MEMZERO(did_dc, SIZEOF(did_dc)); 
  MEMZERO(did_ac, SIZEOF(did_ac)); 
 
  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; 
    if (! did_dc[dctbl]) { 
      htblptr = & cinfo->dc_huff_tbl_ptrs[dctbl]; 
      if (*htblptr == NULL) 
	*htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo); 
      jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[dctbl]); 
      did_dc[dctbl] = TRUE; 
    } 
    if (! did_ac[actbl]) { 
      htblptr = & cinfo->ac_huff_tbl_ptrs[actbl]; 
      if (*htblptr == NULL) 
	*htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo); 
      jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[actbl]); 
      did_ac[actbl] = TRUE; 
    } 
  } 
} 
 
 
#endif /* ENTROPY_OPT_SUPPORTED */ 
 
 
/* 
 * Module initialization routine for Huffman entropy encoding. 
 */ 
 
GLOBAL(void) 
jinit_huff_encoder (j_compress_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_encoder)); 
  cinfo->entropy = (struct jpeg_entropy_encoder *) entropy; 
  entropy->pub.start_pass = start_pass_huff; 
 
  /* Mark tables unallocated */ 
  for (i = 0; i < NUM_HUFF_TBLS; i++) { 
    entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; 
#ifdef ENTROPY_OPT_SUPPORTED 
    entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL; 
#endif 
  } 
}