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1 line
23 KiB
C
1 line
23 KiB
C
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/*
* jchuff.c
*
* Copyright (C) 1991-1994, 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"
/* 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;
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) */
#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
LOCAL void fix_huff_tbl JPP((JCHUFF_TBL * htbl));
/*
* 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;
/* Make sure requested tables are present */
/* (In gather mode, tables need not be allocated yet) */
if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS ||
(cinfo->dc_huff_tbl_ptrs[dctbl] == NULL && !gather_statistics))
ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
if (actbl < 0 || actbl >= NUM_HUFF_TBLS ||
(cinfo->ac_huff_tbl_ptrs[actbl] == NULL && !gather_statistics))
ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
if (gather_statistics) {
#ifdef ENTROPY_OPT_SUPPORTED
/* Allocate and zero the statistics tables */
/* Note that gen_huff_coding expects 257 entries in each table! */
if (entropy->dc_count_ptrs[dctbl] == NULL)
entropy->dc_count_ptrs
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