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/*
* jdhuff.c
*
* Copyright (C) 1991, 1992, 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 decoding routines.
* These routines are invoked via the methods entropy_decode
* and entropy_decoder_init/term.
*/
#include "jinclude.h"
/* Static variables to avoid passing 'round extra parameters */
static decompress_info_ptr dcinfo;
static INT32 get_buffer; /* current bit-extraction buffer */
static int bits_left; /* # of unused bits in it */
LOCAL void
fix_huff_tbl (HUFF_TBL * htbl)
/* Compute derived values for a Huffman table */
{
int p, i, l, si;
char huffsize[257];
UINT16 huffcode[257];
UINT16 code;
/* Figure C.1: make table of Huffman code length for each symbol */
/* Note that this is in code-length order. */
p = 0;
for (l = 1; l <= 16; l++) {
for (i = 1; i <= (int) htbl->bits[l]; i++)
huffsize[p++] = (char) l;
}
huffsize[p] = 0;
/* Figure C.2: generate the codes themselves */
/* Note that this is in code-length order. */
code = 0;
si = huffsize[0];
p = 0;
while (huffsize[p]) {
while (((int) huffsize[p]) == si) {
huffcode[p++] = code;
code++;
}
code <<= 1;
si++;
}
/* We don't bother to fill in the encoding tables ehufco[] and ehufsi[], */
/* since they are not used for decoding. */
/* Figure F.15: generate decoding tables */
p = 0;
for (l = 1; l <= 16; l++) {
if (htbl->bits[l]) {
htbl->valptr[l] = p; /* huffval[] index of 1st sym of code len l */
htbl->mincode[l] = huffcode[p]; /* minimum code of length l */
p += htbl->bits[l];
htbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
} else {
htbl->maxcode[l] = -1;
}
}
htbl->maxcode[17] = 0xFFFFFL; /* ensures huff_DECODE terminates */
}
/* Extract the next N bits from the input stream (N <= 15) */
LOCAL int
get_bits (int nbits)
{
int result;
while (nbits > bits_left) {
int c = JGETC(dcinfo);
get_buffer <<= 8;
get_buffer |= c;
bits_left += 8;
/* If it's 0xFF, check and discard stuffed zero byte */
if (c == 0xff) {
c = JGETC(dcinfo); /* Byte stuffing */
if (c != 0)
ERREXIT1(dcinfo->emethods,
"Unexpected marker 0x%02x in compressed data", c);
}
}
bits_left -= nbits;
result = ((int) (get_buffer >> bits_left)) & ((1 << nbits) - 1);
return result;
}
/* Macro to make things go at some speed! */
#define get_bit() (bits_left ? \
((int) (get_buffer >> (--bits_left))) & 1 : \
get_bits(1))
/* Figure F.16: extract next coded symbol from input stream */
LOCAL int
huff_DECODE (HUFF_TBL * htbl)
{
int l, p;
INT32 code;
code = get_bit();
l = 1;
while (code > htbl->maxcode[l]) {
code = (code << 1) + get_bit();
l++;
}
/* With garbage input we may reach the sentinel value l = 17. */
if (l > 16) {
ERREXIT(dcinfo->emethods, "Corrupted data in JPEG file");
}
p = (int) (htbl->valptr[l] + (code - htbl->mincode[l]));
return (int) htbl->huffval[p];
}
/* Figure F.12: extend sign bit */
/* NB: on some compilers this will only work for s > 0 */
#define huff_EXTEND(x, s) ((x) < (1 << ((s)-1)) ? \
(x) + (-1 << (s)) + 1 : \
(x))
/* Decode a single block's worth of coefficients */
/* Note that only the difference is returned for the DC coefficient */
LOCAL void
decode_one_block (JBLOCK block, HUFF_TBL *dctbl, HUFF_TBL *actbl)
{
int s, k, r, n;
/* zero out the coefficient block */
MEMZERO((void *) block, SIZEOF(JBLOCK));
/* Section F.2.2.1: decode the DC coefficient difference */
s = huff_DECODE(dctbl);
if (s) {
r = get_bits(s);
s = huff_EXTEND(r, s);
}
block[0] = s;
/* Section F.2.2.2: decode the AC coefficients */
for (k = 1; k < DCTSIZE2; k++) {
r = huff_DECODE(actbl);
s = r & 15;
n = r >> 4;
if (s) {
k += n;
r = get_bits(s);
block[k] = huff_EXTEND(r, s);
} else {
if (n != 15)
break;
k += 15;
}
}
}
/*
* Initialize for a Huffman-compressed scan.
* This is invoked after reading the SOS marker.
*/
METHODDEF void
huff_decoder_init (decompress_info_ptr cinfo)
{
short ci;
jpeg_component_info * compptr;
/* Initialize static variables */
dcinfo = cinfo;
bits_left = 0;
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
/* Make sure requested tables are present */
if (cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no] == NULL ||
cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no] == NULL)
ERREXIT(cinfo->emethods, "Use of undefined Huffman table");
/* Compute derived values for Huffman tables */
/* We may do this more than once for same table, but it's not a big deal */
fix_huff_tbl(cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no]);
fix_huff_tbl(cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no]);
/* Initialize DC predictions to 0 */
cinfo->last_dc_val[ci] = 0;
}
/* Initialize restart stuff */
cinfo->restarts_to_go = cinfo->restart_interval;
cinfo->next_restart_num = 0;
}
/*
* Check for a restart marker & resynchronize decoder.
*/
LOCAL void
process_restart (decompress_info_ptr cinfo)
{
int c, nbytes;
short ci;
/* Throw away any partial unread byte */
bits_left = 0;
/* Scan for next JPEG marker */
nbytes = 0;
do {
do { /* skip any non-FF bytes */
nbytes++;
c = JGETC(cinfo);
} while (c != 0xFF);
do { /* skip any duplicate FFs */
nbytes++;
c = JGETC(cinfo);
} while (c == 0xFF);
} while (c == 0); /* repeat if it was a stuffed FF/00 */
if (c != (RST0 + cinfo->next_restart_num))
ERREXIT2(cinfo->emethods, "Found 0x%02x marker instead of RST%d",
c, cinfo->next_restart_num);
if (nbytes != 2)
TRACEMS2(cinfo->emethods, 1, "Skipped %d bytes before RST%d",
nbytes-2, cinfo->next_restart_num);
else
TRACEMS1(cinfo->emethods, 2, "RST%d", cinfo->next_restart_num);
/* Re-initialize DC predictions to 0 */
for (ci = 0; ci < cinfo->comps_in_scan; ci++)
cinfo->last_dc_val[ci] = 0;
/* Update restart state */
cinfo->restarts_to_go = cinfo->restart_interval;
cinfo->next_restart_num++;
cinfo->next_restart_num &= 7;
}
/*
* Decode and return one MCU's worth of Huffman-compressed coefficients.
*/
METHODDEF void
huff_decode (decompress_info_ptr cinfo, JBLOCK *MCU_data)
{
short blkn, ci;
jpeg_component_info * compptr;
/* Account for restart interval, process restart marker if needed */
if (cinfo->restart_interval) {
if (cinfo->restarts_to_go == 0)
process_restart(cinfo);
cinfo->restarts_to_go--;
}
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
ci = cinfo->MCU_membership[blkn];
compptr = cinfo->cur_comp_info[ci];
decode_one_block(MCU_data[blkn],
cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no],
cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no]);
/* Convert DC difference to actual value, update last_dc_val */
MCU_data[blkn][0] += cinfo->last_dc_val[ci];
cinfo->last_dc_val[ci] = MCU_data[blkn][0];
}
}
/*
* Finish up at the end of a Huffman-compressed scan.
*/
METHODDEF void
huff_decoder_term (decompress_info_ptr cinfo)
{
/* No work needed */
}
/*
* The method selection routine for Huffman entropy decoding.
*/
GLOBAL void
jseldhuffman (decompress_info_ptr cinfo)
{
if (! cinfo->arith_code) {
cinfo->methods->entropy_decoder_init = huff_decoder_init;
cinfo->methods->entropy_decode = huff_decode;
cinfo->methods->entropy_decoder_term = huff_decoder_term;
}
}
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