/* | |

* 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 { | |

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 (((INT32) code) >= (((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 INT32 put_buffer = (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 &= (((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 | |

} | |

} |