Alien-FreeImage
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src/Source/LibJPEG/jchuff.c view on Meta::CPAN
/*
* jchuff.c
*
* Copyright (C) 1991-1997, Thomas G. Lane.
* Modified 2006-2013 by Guido Vollbeding.
* 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.
* Both sequential and progressive modes are supported in this single module.
*
* 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.
*
* We do not support output suspension for the progressive JPEG mode, since
* the library currently does not allow multiple-scan files to be written
* with output suspension.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
/* The legal range of a DCT coefficient is
* -1024 .. +1023 for 8-bit data;
* -16384 .. +16383 for 12-bit data.
* Hence the magnitude should always fit in 10 or 14 bits respectively.
*/
#if BITS_IN_JSAMPLE == 8
#define MAX_COEF_BITS 10
#else
#define MAX_COEF_BITS 14
#endif
/* Derived data constructed for each Huffman table */
typedef struct {
unsigned int ehufco[256]; /* code for each symbol */
char ehufsi[256]; /* length of code for each symbol */
/* If no code has been allocated for a symbol S, ehufsi[S] contains 0 */
} c_derived_tbl;
/* 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];
/* Statistics tables for optimization */
long * dc_count_ptrs[NUM_HUFF_TBLS];
long * ac_count_ptrs[NUM_HUFF_TBLS];
/* Following fields used only in progressive mode */
/* Mode flag: TRUE for optimization, FALSE for actual data output */
boolean gather_statistics;
/* next_output_byte/free_in_buffer are local copies of cinfo->dest fields.
*/
JOCTET * next_output_byte; /* => next byte to write in buffer */
size_t free_in_buffer; /* # of byte spaces remaining in buffer */
j_compress_ptr cinfo; /* link to cinfo (needed for dump_buffer) */
/* Coding status for AC components */
int ac_tbl_no; /* the table number of the single component */
unsigned int EOBRUN; /* run length of EOBs */
unsigned int BE; /* # of buffered correction bits before MCU */
src/Source/LibJPEG/jchuff.c view on Meta::CPAN
return; /* no real work */
while (nbits > 0) {
emit_bits_e(entropy, (unsigned int) (*bufstart), 1);
bufstart++;
nbits--;
}
}
/*
* Emit any pending EOBRUN symbol.
*/
LOCAL(void)
emit_eobrun (huff_entropy_ptr entropy)
{
register int temp, nbits;
if (entropy->EOBRUN > 0) { /* if there is any pending EOBRUN */
temp = entropy->EOBRUN;
nbits = 0;
while ((temp >>= 1))
nbits++;
/* safety check: shouldn't happen given limited correction-bit buffer */
if (nbits > 14)
ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);
emit_ac_symbol(entropy, entropy->ac_tbl_no, nbits << 4);
if (nbits)
emit_bits_e(entropy, entropy->EOBRUN, nbits);
entropy->EOBRUN = 0;
/* Emit any buffered correction bits */
emit_buffered_bits(entropy, entropy->bit_buffer, entropy->BE);
entropy->BE = 0;
}
}
/*
* Emit a restart marker & resynchronize predictions.
*/
LOCAL(boolean)
emit_restart_s (working_state * state, int restart_num)
{
int ci;
if (! flush_bits_s(state))
return FALSE;
emit_byte_s(state, 0xFF, return FALSE);
emit_byte_s(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;
}
LOCAL(void)
emit_restart_e (huff_entropy_ptr entropy, int restart_num)
{
int ci;
emit_eobrun(entropy);
if (! entropy->gather_statistics) {
flush_bits_e(entropy);
emit_byte_e(entropy, 0xFF);
emit_byte_e(entropy, JPEG_RST0 + restart_num);
}
if (entropy->cinfo->Ss == 0) {
/* Re-initialize DC predictions to 0 */
for (ci = 0; ci < entropy->cinfo->comps_in_scan; ci++)
entropy->saved.last_dc_val[ci] = 0;
} else {
/* Re-initialize all AC-related fields to 0 */
entropy->EOBRUN = 0;
entropy->BE = 0;
}
}
/*
* MCU encoding for DC initial scan (either spectral selection,
* or first pass of successive approximation).
*/
METHODDEF(boolean)
encode_mcu_DC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
{
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
register int temp, temp2;
register int nbits;
int blkn, ci, tbl;
ISHIFT_TEMPS
entropy->next_output_byte = cinfo->dest->next_output_byte;
entropy->free_in_buffer = cinfo->dest->free_in_buffer;
/* Emit restart marker if needed */
if (cinfo->restart_interval)
if (entropy->restarts_to_go == 0)
emit_restart_e(entropy, entropy->next_restart_num);
/* Encode the MCU data blocks */
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
ci = cinfo->MCU_membership[blkn];
tbl = cinfo->cur_comp_info[ci]->dc_tbl_no;
/* Compute the DC value after the required point transform by Al.
* This is simply an arithmetic right shift.
*/
src/Source/LibJPEG/jchuff.c view on Meta::CPAN
}
/* 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, tbl;
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!
*/
if (cinfo->progressive_mode)
/* Flush out buffered data (all we care about is counting the EOB symbol) */
emit_eobrun(entropy);
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];
/* DC needs no table for refinement scan */
if (cinfo->Ss == 0 && cinfo->Ah == 0) {
tbl = compptr->dc_tbl_no;
if (! did_dc[tbl]) {
htblptr = & cinfo->dc_huff_tbl_ptrs[tbl];
if (*htblptr == NULL)
*htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[tbl]);
did_dc[tbl] = TRUE;
}
}
/* AC needs no table when not present */
if (cinfo->Se) {
tbl = compptr->ac_tbl_no;
if (! did_ac[tbl]) {
htblptr = & cinfo->ac_huff_tbl_ptrs[tbl];
if (*htblptr == NULL)
*htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[tbl]);
did_ac[tbl] = TRUE;
}
}
}
}
/*
* 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.
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