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/*
* jchuff.c
*
* Copyright (C) 1991, 1992, 1993, 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.
* These routines are invoked via the methods entropy_encode,
* entropy_encode_init/term, and entropy_optimize.
*/
#include "jinclude.h"
/* Static variables to avoid passing 'round extra parameters */
static compress_info_ptr cinfo;
static INT32 huff_put_buffer; /* current bit-accumulation buffer */
static int huff_put_bits; /* # of bits now in it */
static char * output_buffer; /* output buffer */
static int bytes_in_buffer;
LOCAL void
fix_huff_tbl (HUFF_TBL * htbl)
/* Compute derived values for a Huffman table */
{
int p, i, l, lastp, 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;
lastp = p;
/* 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++;
}
/* Figure C.3: generate encoding tables */
/* These are code and size indexed by symbol value */
/* Set any codeless symbols to have code length 0;
* this allows emit_bits to detect any attempt to emit such symbols.
*/
MEMZERO(htbl->priv.enc.ehufsi, SIZEOF(htbl->priv.enc.ehufsi));
for (p = 0; p < lastp; p++) {
htbl->priv.enc.ehufco[htbl->huffval[p]] = huffcode[p];
htbl->priv.enc.ehufsi[htbl->huffval[p]] = huffsize[p];
}
}
/* Outputting bytes to the file */
LOCAL void
flush_bytes (void)
{
if (bytes_in_buffer)
(*cinfo->methods->entropy_output) (cinfo, output_buffer, bytes_in_buffer);
bytes_in_buffer = 0;
}
#define emit_byte(val) \
MAKESTMT( if (bytes_in_buffer >= JPEG_BUF_SIZE) \
flush_bytes(); \
output_buffer[bytes_in_buffer++] = (char) (val); )
/* Outputting bits to the file */
/* Only the right 24 bits of huff_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 huff_put_buffer
* between calls, so 24 bits are sufficient.
*/
INLINE
LOCAL void
emit_bits (UINT16 code, int size)
{
/* This routine is heavily used, so it's worth coding tightly. */
register INT32 put_buffer = code;
register int put_bits = huff_put_bits;
/* if size is 0, caller used an invalid Huffman table entry */
if (size == 0)
ERREXIT(cinfo->emethods, "Missing Huffman code table entry");
put_buffer &= (((INT32) 1) << size) - 1; /* Mask off any excess bits in code */
put_bits += size; /* new number of bits in buffer */
put_buffer <<= 24 - put_bits; /* align incoming bits */
put_buffer |= huff_put_buffer; /* and merge with old buffer contents */
while (put_bits >= 8) {
int c = (int) ((put_buffer >> 16) & 0xFF);
emit_byte(c);
if (c == 0xFF) { /* need to stuff a zero byte? */
emit_byte(0);
}
put_buffer <<= 8;
put_bits -= 8;
}
huff_put_buffer = put_buffer; /* Update global variables */
huff_put_bits = put_bits;
}
LOCAL void
flush_bits (void)
{
emit_bits((UINT16) 0x7F, 7); /* fill any partial byte with ones */
huff_put_buffer = 0; /* and reset bit-buffer to empty */
huff_put_bits = 0;
}
/* Encode a single block's worth of coefficients */
/* Note that the DC coefficient has already been converted to a difference */
LOCAL void
encode_one_block (JBLOCK block, HUFF_TBL *dctbl, HUFF_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];
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;
}
/* Emit the Huffman-coded symbol for the number of bits */
emit_bits(dctbl->priv.enc.ehufco[nbits], dctbl->priv.enc.ehufsi[nbits]);
/* 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 */
emit_bits((UINT16) temp2, 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[k]) == 0) {
r++;
} else {
/* if run length > 15, must emit special run-length-16 codes (0xF0) */
while (r > 15) {
emit_bits(actbl->priv.enc.ehufco[0xF0], actbl->priv.enc.ehufsi[0xF0]);
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++;
/* Emit Huffman symbol for run length / number of bits */
i = (r << 4) + nbits;
emit_bits(actbl->priv.enc.ehufco[i], actbl->priv.enc.ehufsi[i]);
/* Emit that number of bits of the value, if positive, */
/* or the complement of its magnitude, if negative. */
emit_bits((UINT16) temp2, nbits);
r = 0;
}
}
/* If the last coef(s) were zero, emit an end-of-block code */
if (r > 0)
emit_bits(actbl->priv.enc.ehufco[0], actbl->priv.enc.ehufsi[0]);
}
/*
* Initialize for a Huffman-compressed scan.
* This is invoked after writing the SOS marker.
* The pipeline controller must establish the entropy_output method pointer
* before calling this routine.
*/
METHODDEF void
huff_init (compress_info_ptr xinfo)
{
short ci;
jpeg_component_info * compptr;
/* Initialize static variables */
cinfo = xinfo;
huff_put_buffer = 0;
huff_put_bits = 0;
/* Initialize the output buffer */
output_buffer = (char *) (*cinfo->emethods->alloc_small)
((size_t) JPEG_BUF_SIZE);
bytes_in_buffer = 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;
}
/*
* Emit a restart marker & resynchronize predictions.
*/
LOCAL void
emit_restart (compress_info_ptr cinfo)
{
short ci;
flush_bits();
emit_byte(0xFF);
emit_byte(RST0 + 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;
}
/*
* Encode and output one MCU's worth of Huffman-compressed coefficients.
*/
METHODDEF void
huff_encode (compress_info_ptr cinfo, JBLOCK *MCU_data)
{
short blkn, ci;
jpeg_component_info * compptr;
JCOEF temp;
/* Account for restart interval, emit restart marker if needed */
if (cinfo->restart_interval) {
if (cinfo->restarts_to_go == 0)
emit_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];
/* Convert DC value to difference, update last_dc_val */
temp = MCU_data[blkn][0];
MCU_data[blkn][0] -= cinfo->last_dc_val[ci];
cinfo->last_dc_val[ci] = temp;
encode_one_block(MCU_data[blkn],
cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no],
cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no]);
}
}
/*
* Finish up at the end of a Huffman-compressed scan.
*/
METHODDEF void
huff_term (compress_info_ptr cinfo)
{
/* Flush out the last data */
flush_bits();
flush_bytes();
/* Release the I/O buffer */
(*cinfo->emethods->free_small) ((void *) output_buffer);
}
/*
* 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.
*/
#ifdef ENTROPY_OPT_SUPPORTED
/* These are static so htest_one_block can find 'em */
static long * dc_count_ptrs[NUM_HUFF_TBLS];
static long * ac_count_ptrs[NUM_HUFF_TBLS];
LOCAL void
gen_huff_coding (compress_info_ptr cinfo, HUFF_TBL *htbl, long freq[])
/* Generate the optimal coding for the given counts */
{
#define MAX_CLEN 32 /* assumed maximum initial code length */
UINT8 bits[MAX_CLEN+1]; /* bits[k] = # of symbols with code length k */
short codesize[257]; /* codesize[k] = code length of symbol k */
short 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->emethods, "Huffman code size table 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++;
}
}
}
}
/* Process a single block's worth of coefficients */
/* Note that the DC coefficient has already been converted to a difference */
LOCAL void
htest_one_block (JBLOCK block, JCOEF block0,
long dc_counts[], long ac_counts[])
{
register INT32 temp;
register int nbits;
register int k, r;
/* Encode the DC coefficient difference per section F.1.2.1 */
/* Find the number of bits needed for the magnitude of the coefficient */
temp = block0;
if (temp < 0) temp = -temp;
for (nbits = 0; 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[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;
for (nbits = 0; temp; nbits++)
temp >>= 1;
/* 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.
*/
LOCAL void
htest_encode (compress_info_ptr cinfo, JBLOCK *MCU_data)
{
short blkn, ci;
jpeg_component_info * compptr;
/* Take care of restart intervals if needed */
if (cinfo->restart_interval) {
if (cinfo->restarts_to_go == 0) {
/* 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->restarts_to_go--;
}
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
ci = cinfo->MCU_membership[blkn];
compptr = cinfo->cur_comp_info[ci];
/* NB: unlike the real entropy encoder, we may not change the input data */
htest_one_block(MCU_data[blkn],
(JCOEF) (MCU_data[blkn][0] - cinfo->last_dc_val[ci]),
dc_count_ptrs[compptr->dc_tbl_no],
ac_count_ptrs[compptr->ac_tbl_no]);
cinfo->last_dc_val[ci] = MCU_data[blkn][0];
}
}
/*
* Find the best coding parameters for a Huffman-coded scan.
* When called, the scan data has already been converted to a sequence of
* MCU groups of quantized coefficients, which are stored in a "big" array.
* The source_method knows how to iterate through that array.
* On return, the MCU data is unmodified, but the Huffman tables referenced
* by the scan components may have been altered.
*/
METHODDEF void
huff_optimize (compress_info_ptr cinfo, MCU_output_caller_ptr source_method)
/* Optimize Huffman-coding parameters (Huffman symbol table) */
{
int i, tbl;
HUFF_TBL **htblptr;
/* Allocate and zero the count tables */
/* Note that gen_huff_coding expects 257 entries in each table! */
for (i = 0; i < NUM_HUFF_TBLS; i++) {
dc_count_ptrs[i] = NULL;
ac_count_ptrs[i] = NULL;
}
for (i = 0; i < cinfo->comps_in_scan; i++) {
/* Create DC table */
tbl = cinfo->cur_comp_info[i]->dc_tbl_no;
if (dc_count_ptrs[tbl] == NULL) {
dc_count_ptrs[tbl] = (long *) (*cinfo->emethods->alloc_small)
(257 * SIZEOF(long));
MEMZERO(dc_count_ptrs[tbl], 257 * SIZEOF(long));
}
/* Create AC table */
tbl = cinfo->cur_comp_info[i]->ac_tbl_no;
if (ac_count_ptrs[tbl] == NULL) {
ac_count_ptrs[tbl] = (long *) (*cinfo->emethods->alloc_small)
(257 * SIZEOF(long));
MEMZERO(ac_count_ptrs[tbl], 257 * SIZEOF(long));
}
}
/* Initialize DC predictions to 0 */
for (i = 0; i < cinfo->comps_in_scan; i++) {
cinfo->last_dc_val[i] = 0;
}
/* Initialize restart stuff */
cinfo->restarts_to_go = cinfo->restart_interval;
/* Scan the MCU data, count symbol uses */
(*source_method) (cinfo, htest_encode);
/* Now generate optimal Huffman tables */
for (tbl = 0; tbl < NUM_HUFF_TBLS; tbl++) {
if (dc_count_ptrs[tbl] != NULL) {
htblptr = & cinfo->dc_huff_tbl_ptrs[tbl];
if (*htblptr == NULL)
*htblptr = (HUFF_TBL *) (*cinfo->emethods->alloc_small) (SIZEOF(HUFF_TBL));
/* Set sent_table FALSE so updated table will be written to JPEG file. */
(*htblptr)->sent_table = FALSE;
/* Compute the optimal Huffman encoding */
gen_huff_coding(cinfo, *htblptr, dc_count_ptrs[tbl]);
/* Release the count table */
(*cinfo->emethods->free_small) ((void *) dc_count_ptrs[tbl]);
}
if (ac_count_ptrs[tbl] != NULL) {
htblptr = & cinfo->ac_huff_tbl_ptrs[tbl];
if (*htblptr == NULL)
*htblptr = (HUFF_TBL *) (*cinfo->emethods->alloc_small) (SIZEOF(HUFF_TBL));
/* Set sent_table FALSE so updated table will be written to JPEG file. */
(*htblptr)->sent_table = FALSE;
/* Compute the optimal Huffman encoding */
gen_huff_coding(cinfo, *htblptr, ac_count_ptrs[tbl]);
/* Release the count table */
(*cinfo->emethods->free_small) ((void *) ac_count_ptrs[tbl]);
}
}
}
#endif /* ENTROPY_OPT_SUPPORTED */
/*
* The method selection routine for Huffman entropy encoding.
*/
GLOBAL void
jselchuffman (compress_info_ptr cinfo)
{
if (! cinfo->arith_code) {
cinfo->methods->entropy_encode_init = huff_init;
cinfo->methods->entropy_encode = huff_encode;
cinfo->methods->entropy_encode_term = huff_term;
#ifdef ENTROPY_OPT_SUPPORTED
cinfo->methods->entropy_optimize = huff_optimize;
/* The standard Huffman tables are only valid for 8-bit data precision.
* If the precision is higher, force optimization on so that usable
* tables will be computed. This test can be removed if default tables
* are supplied that are valid for the desired precision.
*/
if (cinfo->data_precision > 8)
cinfo->optimize_coding = TRUE;
if (cinfo->optimize_coding)
cinfo->total_passes++; /* one pass needed for entropy optimization */
#endif
}
}
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