817 lines
24 KiB
C++
817 lines
24 KiB
C++
// * jchuff.c
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// *
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// * Copyright (C) 1991-1995, Thomas G. Lane.
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// * This file is part of the Independent JPEG Group's software.
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// * For conditions of distribution and use, see the accompanying README file.
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// *
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// * This file contains Huffman entropy encoding routines.
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// *
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// * Much of the complexity here has to do with supporting output suspension.
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// * If the data destination module demands suspension, we want to be able to
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// * back up to the start of the current MCU. To do this, we copy state
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// * variables into local working storage, and update them back to the
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// * permanent JPEG objects only upon successful completion of an MCU.
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#define JPEG_INTERNALS
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#include "JINCLUDE.h"
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#include "JPEGLIB.h"
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#include "JCHUFF.h" // Declarations shared with jcphuff.c
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// Expanded entropy encoder object for Huffman encoding.
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// *
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// * The savable_state subrecord contains fields that change within an MCU,
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// * but must not be updated permanently until we complete the MCU.
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typedef struct {
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INT32 put_buffer; // current bit-accumulation buffer
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int put_bits; // # of bits now in it
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int last_dc_val[MAX_COMPS_IN_SCAN]; // last DC coef for each component
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} savable_state;
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// This macro is to work around compilers with missing or broken
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// * structure assignment. You'll need to fix this code if you have
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// * such a compiler and you change MAX_COMPS_IN_SCAN.
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#ifndef NO_STRUCT_ASSIGN
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#define ASSIGN_STATE(dest,src) ((dest) = (src))
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#else
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#if MAX_COMPS_IN_SCAN == 4
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#define ASSIGN_STATE(dest,src) \
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((dest).put_buffer = (src).put_buffer, \
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(dest).put_bits = (src).put_bits, \
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(dest).last_dc_val[0] = (src).last_dc_val[0], \
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(dest).last_dc_val[1] = (src).last_dc_val[1], \
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(dest).last_dc_val[2] = (src).last_dc_val[2], \
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(dest).last_dc_val[3] = (src).last_dc_val[3])
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#endif
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#endif
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typedef struct {
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struct jpeg_entropy_encoder pub; // public fields
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savable_state saved; // Bit buffer & DC state at start of MCU
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// These fields are NOT loaded into local working state.
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unsigned int restarts_to_go; // MCUs left in this restart interval
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int next_restart_num; // next restart number to write (0-7)
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// Pointers to derived tables (these workspaces have image lifespan)
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c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
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c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
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#ifdef ENTROPY_OPT_SUPPORTED // Statistics tables for optimization
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LONG * dc_count_ptrs[NUM_HUFF_TBLS];
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LONG * ac_count_ptrs[NUM_HUFF_TBLS];
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#endif
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} huff_entropy_encoder;
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typedef huff_entropy_encoder * huff_entropy_ptr;
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// Working state while writing an MCU.
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// * This struct contains all the fields that are needed by subroutines.
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typedef struct {
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JOCTET * next_output_byte; // => next byte to write in buffer
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size_t free_in_buffer; // # of byte spaces remaining in buffer
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savable_state cur; // Current bit buffer & DC state
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j_compress_ptr cinfo; // dump_buffer needs access to this
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} working_state;
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// Forward declarations
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METHODDEF boolean encode_mcu_huff JPP((j_compress_ptr cinfo,
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JBLOCKROW *MCU_data));
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METHODDEF void finish_pass_huff JPP((j_compress_ptr cinfo));
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#ifdef ENTROPY_OPT_SUPPORTED
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METHODDEF boolean encode_mcu_gather JPP((j_compress_ptr cinfo,
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JBLOCKROW *MCU_data));
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METHODDEF void finish_pass_gather JPP((j_compress_ptr cinfo));
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#endif
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// * Initialize for a Huffman-compressed scan.
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// * If gather_statistics is TRUE, we do not output anything during the scan,
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// * just count the Huffman symbols used and generate Huffman code tables.
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METHODDEF void
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start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics)
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{
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huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
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int ci, dctbl, actbl;
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jpeg_component_info * compptr;
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if (gather_statistics) {
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#ifdef ENTROPY_OPT_SUPPORTED
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entropy->pub.encode_mcu = encode_mcu_gather;
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entropy->pub.finish_pass = finish_pass_gather;
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#else
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ERREXIT(cinfo, JERR_NOT_COMPILED);
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#endif
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} else {
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entropy->pub.encode_mcu = encode_mcu_huff;
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entropy->pub.finish_pass = finish_pass_huff;
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}
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for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
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compptr = cinfo->cur_comp_info[ci];
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dctbl = compptr->dc_tbl_no;
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actbl = compptr->ac_tbl_no;
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// Make sure requested tables are present
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// (In gather mode, tables need not be allocated yet)
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if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS ||
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(cinfo->dc_huff_tbl_ptrs[dctbl] == NULL && !gather_statistics))
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ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
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if (actbl < 0 || actbl >= NUM_HUFF_TBLS ||
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(cinfo->ac_huff_tbl_ptrs[actbl] == NULL && !gather_statistics))
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ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
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if (gather_statistics) {
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#ifdef ENTROPY_OPT_SUPPORTED
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// Allocate and zero the statistics tables
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// Note that jpeg_gen_optimal_table expects 257 entries in each table!
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if (entropy->dc_count_ptrs[dctbl] == NULL)
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entropy->dc_count_ptrs[dctbl] = (LONG *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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257 * SIZEOF(LONG));
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MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * SIZEOF(LONG));
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if (entropy->ac_count_ptrs[actbl] == NULL)
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entropy->ac_count_ptrs[actbl] = (LONG *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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257 * SIZEOF(LONG));
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MEMZERO(entropy->ac_count_ptrs[actbl], 257 * SIZEOF(LONG));
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#endif
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} else {
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// Compute derived values for Huffman tables
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// We may do this more than once for a table, but it's not expensive
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jpeg_make_c_derived_tbl(cinfo, cinfo->dc_huff_tbl_ptrs[dctbl],
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& entropy->dc_derived_tbls[dctbl]);
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jpeg_make_c_derived_tbl(cinfo, cinfo->ac_huff_tbl_ptrs[actbl],
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& entropy->ac_derived_tbls[actbl]);
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}
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// Initialize DC predictions to 0
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entropy->saved.last_dc_val[ci] = 0;
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}
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// Initialize bit buffer to empty
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entropy->saved.put_buffer = 0;
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entropy->saved.put_bits = 0;
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// Initialize restart stuff
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entropy->restarts_to_go = cinfo->restart_interval;
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entropy->next_restart_num = 0;
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}
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// * Compute the derived values for a Huffman table.
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// * Note this is also used by jcphuff.c.
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GLOBAL void
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jpeg_make_c_derived_tbl (j_compress_ptr cinfo, JHUFF_TBL * htbl,
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c_derived_tbl ** pdtbl)
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{
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c_derived_tbl *dtbl;
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int p, i, l, lastp, si;
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char huffsize[257];
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unsigned int huffcode[257];
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unsigned int code;
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// Allocate a workspace if we haven't already done so.
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if (*pdtbl == NULL)
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*pdtbl = (c_derived_tbl *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(c_derived_tbl));
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dtbl = *pdtbl;
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// Figure C.1: make table of Huffman code length for each symbol
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// Note that this is in code-length order.
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p = 0;
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for (l = 1; l <= 16; l++) {
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for (i = 1; i <= (int) htbl->bits[l]; i++)
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huffsize[p++] = (char) l;
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}
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huffsize[p] = 0;
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lastp = p;
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// Figure C.2: generate the codes themselves
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// Note that this is in code-length order.
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code = 0;
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si = huffsize[0];
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p = 0;
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while (huffsize[p]) {
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while (((int) huffsize[p]) == si) {
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huffcode[p++] = code;
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code++;
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}
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code <<= 1;
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si++;
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}
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// Figure C.3: generate encoding tables
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// These are code and size indexed by symbol value
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// Set any codeless symbols to have code length 0;
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// * this allows emit_bits to detect any attempt to emit such symbols.
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MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));
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for (p = 0; p < lastp; p++) {
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dtbl->ehufco[htbl->huffval[p]] = huffcode[p];
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dtbl->ehufsi[htbl->huffval[p]] = huffsize[p];
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}
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}
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// Outputting bytes to the file
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// Emit a byte, taking 'action' if must suspend.
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#define emit_byte(state,val,action) \
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{ *(state)->next_output_byte++ = (JOCTET) (val); \
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if (--(state)->free_in_buffer == 0) \
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if (! dump_buffer(state)) \
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{ action; } }
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LOCAL boolean
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dump_buffer (working_state * state)
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// Empty the output buffer; return TRUE if successful, FALSE if must suspend
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{
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struct jpeg_destination_mgr * dest = state->cinfo->dest;
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if (! (*dest->empty_output_buffer) (state->cinfo))
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return FALSE;
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// After a successful buffer dump, must reset buffer pointers
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state->next_output_byte = dest->next_output_byte;
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state->free_in_buffer = dest->free_in_buffer;
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return TRUE;
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}
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// Outputting bits to the file
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// Only the right 24 bits of put_buffer are used; the valid bits are
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// * left-justified in this part. At most 16 bits can be passed to emit_bits
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// * in one call, and we never retain more than 7 bits in put_buffer
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// * between calls, so 24 bits are sufficient.
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INLINE
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LOCAL boolean
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emit_bits (working_state * state, unsigned int code, int size)
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// Emit some bits; return TRUE if successful, FALSE if must suspend
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{
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// This routine is heavily used, so it's worth coding tightly.
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register INT32 put_buffer = (INT32) code;
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register int put_bits = state->cur.put_bits;
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// if size is 0, caller used an invalid Huffman table entry
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if (size == 0)
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ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);
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put_buffer &= (((INT32) 1)<<size) - 1; // mask off any extra bits in code
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put_bits += size; // new number of bits in buffer
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put_buffer <<= 24 - put_bits; // align incoming bits
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put_buffer |= state->cur.put_buffer; // and merge with old buffer contents
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while (put_bits >= 8) {
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int c = (int) ((put_buffer >> 16) & 0xFF);
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emit_byte(state, c, return FALSE);
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if (c == 0xFF) { // need to stuff a zero byte?
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emit_byte(state, 0, return FALSE);
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}
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put_buffer <<= 8;
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put_bits -= 8;
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}
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state->cur.put_buffer = put_buffer; // update state variables
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state->cur.put_bits = put_bits;
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return TRUE;
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}
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LOCAL boolean
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flush_bits (working_state * state)
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{
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if (! emit_bits(state, 0x7F, 7)) // fill any partial byte with ones
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return FALSE;
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state->cur.put_buffer = 0; // and reset bit-buffer to empty
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state->cur.put_bits = 0;
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return TRUE;
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}
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// Encode a single block's worth of coefficients
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LOCAL boolean
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encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val,
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c_derived_tbl *dctbl, c_derived_tbl *actbl)
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{
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register int temp, temp2;
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register int nbits;
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register int k, r, i;
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// Encode the DC coefficient difference per section F.1.2.1
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temp = temp2 = block[0] - last_dc_val;
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if (temp < 0) {
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temp = -temp; // temp is abs value of input
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// For a negative input, want temp2 = bitwise complement of abs(input)
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// This code assumes we are on a two's complement machine
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temp2--;
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}
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// Find the number of bits needed for the magnitude of the coefficient
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nbits = 0;
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while (temp) {
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nbits++;
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temp >>= 1;
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}
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// Emit the Huffman-coded symbol for the number of bits
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if (! emit_bits(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))
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return FALSE;
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// Emit that number of bits of the value, if positive,
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// or the complement of its magnitude, if negative.
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if (nbits) // emit_bits rejects calls with size 0
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if (! emit_bits(state, (unsigned int) temp2, nbits))
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return FALSE;
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// Encode the AC coefficients per section F.1.2.2
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r = 0; // r = run length of zeros
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for (k = 1; k < DCTSIZE2; k++) {
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if ((temp = block[jpeg_natural_order[k]]) == 0) {
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r++;
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} else {
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// if run length > 15, must emit special run-length-16 codes (0xF0)
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while (r > 15) {
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if (! emit_bits(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0]))
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return FALSE;
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r -= 16;
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}
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temp2 = temp;
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if (temp < 0) {
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temp = -temp; // temp is abs value of input
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// This code assumes we are on a two's complement machine
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temp2--;
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}
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// Find the number of bits needed for the magnitude of the coefficient
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nbits = 1; // there must be at least one 1 bit
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while ((temp >>= 1))
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nbits++;
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// Emit Huffman symbol for run length / number of bits
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i = (r << 4) + nbits;
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if (! emit_bits(state, actbl->ehufco[i], actbl->ehufsi[i]))
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return FALSE;
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// Emit that number of bits of the value, if positive,
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// or the complement of its magnitude, if negative.
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if (! emit_bits(state, (unsigned int) temp2, nbits))
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return FALSE;
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r = 0;
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}
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}
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// If the last coef(s) were zero, emit an end-of-block code
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if (r > 0)
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if (! emit_bits(state, actbl->ehufco[0], actbl->ehufsi[0]))
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return FALSE;
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return TRUE;
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}
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// * Emit a restart marker & resynchronize predictions.
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LOCAL boolean
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emit_restart (working_state * state, int restart_num)
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{
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int ci;
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if (! flush_bits(state))
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return FALSE;
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emit_byte(state, 0xFF, return FALSE);
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emit_byte(state, JPEG_RST0 + restart_num, return FALSE);
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// Re-initialize DC predictions to 0
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for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)
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state->cur.last_dc_val[ci] = 0;
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// The restart counter is not updated until we successfully write the MCU.
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return TRUE;
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}
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// * Encode and output one MCU's worth of Huffman-compressed coefficients.
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METHODDEF boolean
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encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
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{
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huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
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working_state state;
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int blkn, ci;
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jpeg_component_info * compptr;
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// Load up working state
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state.next_output_byte = cinfo->dest->next_output_byte;
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state.free_in_buffer = cinfo->dest->free_in_buffer;
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ASSIGN_STATE(state.cur, entropy->saved);
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state.cinfo = cinfo;
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// Emit restart marker if needed
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if (cinfo->restart_interval) {
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if (entropy->restarts_to_go == 0)
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if (! emit_restart(&state, entropy->next_restart_num))
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return FALSE;
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}
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// Encode the MCU data blocks
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for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
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ci = cinfo->MCU_membership[blkn];
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compptr = cinfo->cur_comp_info[ci];
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if (! encode_one_block(&state,
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MCU_data[blkn][0], state.cur.last_dc_val[ci],
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entropy->dc_derived_tbls[compptr->dc_tbl_no],
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entropy->ac_derived_tbls[compptr->ac_tbl_no]))
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return FALSE;
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// Update last_dc_val
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state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
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}
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// Completed MCU, so update state
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cinfo->dest->next_output_byte = state.next_output_byte;
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cinfo->dest->free_in_buffer = state.free_in_buffer;
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ASSIGN_STATE(entropy->saved, state.cur);
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// Update restart-interval state too
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if (cinfo->restart_interval) {
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if (entropy->restarts_to_go == 0) {
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entropy->restarts_to_go = cinfo->restart_interval;
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entropy->next_restart_num++;
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entropy->next_restart_num &= 7;
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}
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entropy->restarts_to_go--;
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}
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return TRUE;
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}
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// * Finish up at the end of a Huffman-compressed scan.
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METHODDEF void
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finish_pass_huff (j_compress_ptr cinfo)
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{
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huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
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working_state state;
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// Load up working state ... flush_bits needs it
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state.next_output_byte = cinfo->dest->next_output_byte;
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state.free_in_buffer = cinfo->dest->free_in_buffer;
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ASSIGN_STATE(state.cur, entropy->saved);
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state.cinfo = cinfo;
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|
|
|
// 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.
|
|
// *
|
|
// * This actually is optimization, in the sense that we find the best possible
|
|
// * Huffman table(s) for the given data. 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 an
|
|
// * optimal Huffman coding tree for the observed counts.
|
|
// *
|
|
// * 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 the JPEG spec. This method is *not*
|
|
// * optimal; it may not choose the best possible limited-length code. But
|
|
// * since the symbols involved are infrequently used, it's not clear that
|
|
// * going to extra trouble is worthwhile.
|
|
|
|
#ifdef ENTROPY_OPT_SUPPORTED
|
|
|
|
|
|
// Process a single block's worth of coefficients
|
|
|
|
LOCAL void
|
|
htest_one_block (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;
|
|
}
|
|
|
|
// 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++;
|
|
|
|
// 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(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 optimal coding for the given counts, fill htbl.
|
|
// * Note this is also used by jcphuff.c.
|
|
|
|
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 there is 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 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
|
|
}
|
|
}
|