+++ /dev/null
-/*
- * jchuff.c
- *
- * Copyright (C) 1991-1997, 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"
-#include "jchuff.h" /* Declarations shared with jcphuff.c */
-
-
-/* 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];
-
-#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
-
-
-/*
- * 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;
- if (gather_statistics) {
-#ifdef ENTROPY_OPT_SUPPORTED
- /* Check for invalid table indexes */
- /* (make_c_derived_tbl does this in the other path) */
- if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS)
- ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
- if (actbl < 0 || actbl >= NUM_HUFF_TBLS)
- ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
- /* Allocate and zero the statistics tables */
- /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
- if (entropy->dc_count_ptrs[dctbl] == NULL)
- entropy->dc_count_ptrs[dctbl] = (long *)
- (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
- 257 * SIZEOF(long));
- MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * SIZEOF(long));
- if (entropy->ac_count_ptrs[actbl] == NULL)
- entropy->ac_count_ptrs[actbl] = (long *)
- (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
- 257 * SIZEOF(long));
- MEMZERO(entropy->ac_count_ptrs[actbl], 257 * SIZEOF(long));
-#endif
- } else {
- /* Compute derived values for Huffman tables */
- /* We may do this more than once for a table, but it's not expensive */
- jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl,
- & entropy->dc_derived_tbls[dctbl]);
- jpeg_make_c_derived_tbl(cinfo, FALSE, actbl,
- & entropy->ac_derived_tbls[actbl]);
- }
- /* Initialize DC predictions to 0 */
- entropy->saved.last_dc_val[ci] = 0;
- }
-
- /* Initialize bit buffer to empty */
- entropy->saved.put_buffer = 0;
- entropy->saved.put_bits = 0;
-
- /* Initialize restart stuff */
- entropy->restarts_to_go = cinfo->restart_interval;
- entropy->next_restart_num = 0;
-}
-
-
-/*
- * Compute the derived values for a Huffman table.
- * This routine also performs some validation checks on the table.
- *
- * Note this is also used by jcphuff.c.
- */
-
-GLOBAL(void)
-jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno,
- c_derived_tbl ** pdtbl)
-{
- JHUFF_TBL *htbl;
- c_derived_tbl *dtbl;
- int p, i, l, lastp, si, maxsymbol;
- char huffsize[257];
- unsigned int huffcode[257];
- unsigned int code;
-
- /* Note that huffsize[] and huffcode[] are filled in code-length order,
- * paralleling the order of the symbols themselves in htbl->huffval[].
- */
-
- /* Find the input Huffman table */
- if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
- ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
- htbl =
- isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
- if (htbl == NULL)
- ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
-
- /* Allocate a workspace if we haven't already done so. */
- if (*pdtbl == NULL)
- *pdtbl = (c_derived_tbl *)
- (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
- SIZEOF(c_derived_tbl));
- dtbl = *pdtbl;
-
- /* Figure C.1: make table of Huffman code length for each symbol */
-
- p = 0;
- for (l = 1; l <= 16; l++) {
- i = (int) htbl->bits[l];
- if (i < 0 || p + i > 256) /* protect against table overrun */
- ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
- while (i--)
- huffsize[p++] = (char) l;
- }
- huffsize[p] = 0;
- lastp = p;
-
- /* Figure C.2: generate the codes themselves */
- /* We also validate that the counts represent a legal Huffman code tree. */
-
- code = 0;
- si = huffsize[0];
- p = 0;
- while (huffsize[p]) {
- while (((int) huffsize[p]) == si) {
- huffcode[p++] = code;
- code++;
- }
- /* code is now 1 more than the last code used for codelength si; but
- * it must still fit in si bits, since no code is allowed to be all ones.
- */
- if (((INT32) code) >= (((INT32) 1) << si))
- ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
- code <<= 1;
- si++;
- }
-
- /* Figure C.3: generate encoding tables */
- /* These are code and size indexed by symbol value */
-
- /* Set all codeless symbols to have code length 0;
- * this lets us detect duplicate VAL entries here, and later
- * allows emit_bits to detect any attempt to emit such symbols.
- */
- MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));
-
- /* This is also a convenient place to check for out-of-range
- * and duplicated VAL entries. We allow 0..255 for AC symbols
- * but only 0..15 for DC. (We could constrain them further
- * based on data depth and mode, but this seems enough.)
- */
- maxsymbol = isDC ? 15 : 255;
-
- for (p = 0; p < lastp; p++) {
- i = htbl->huffval[p];
- if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
- ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
- dtbl->ehufco[i] = huffcode[p];
- dtbl->ehufsi[i] = huffsize[p];
- }
-}
-
-
-/* Outputting bytes to the file */
-
-/* Emit a byte, taking 'action' if must suspend. */
-#define emit_byte(state,val,action) \
- { *(state)->next_output_byte++ = (JOCTET) (val); \
- if (--(state)->free_in_buffer == 0) \
- if (! dump_buffer(state)) \
- { action; } }
-
-
-LOCAL(boolean)
-dump_buffer (working_state * state)
-/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
-{
- struct jpeg_destination_mgr * dest = state->cinfo->dest;
-
- if (! (*dest->empty_output_buffer) (state->cinfo))
- return FALSE;
- /* After a successful buffer dump, must reset buffer pointers */
- state->next_output_byte = dest->next_output_byte;
- state->free_in_buffer = dest->free_in_buffer;
- return TRUE;
-}
-
-
-/* Outputting bits to the file */
-
-/* Only the right 24 bits of 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 put_buffer
- * between calls, so 24 bits are sufficient.
- */
-
-INLINE
-LOCAL(boolean)
-emit_bits (working_state * state, unsigned int code, int size)
-/* Emit some bits; return TRUE if successful, FALSE if must suspend */
-{
- /* This routine is heavily used, so it's worth coding tightly. */
- register INT32 put_buffer = (INT32) code;
- register int put_bits = state->cur.put_bits;
-
- /* if size is 0, caller used an invalid Huffman table entry */
- if (size == 0)
- ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);
-
- put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
-
- put_bits += size; /* new number of bits in buffer */
-
- put_buffer <<= 24 - put_bits; /* align incoming bits */
-
- put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */
-
- while (put_bits >= 8) {
- int c = (int) ((put_buffer >> 16) & 0xFF);
-
- emit_byte(state, c, return FALSE);
- if (c == 0xFF) { /* need to stuff a zero byte? */
- emit_byte(state, 0, return FALSE);
- }
- put_buffer <<= 8;
- put_bits -= 8;
- }
-
- state->cur.put_buffer = put_buffer; /* update state variables */
- state->cur.put_bits = put_bits;
-
- return TRUE;
-}
-
-
-LOCAL(boolean)
-flush_bits (working_state * state)
-{
- if (! emit_bits(state, 0x7F, 7)) /* fill any partial byte with ones */
- return FALSE;
- state->cur.put_buffer = 0; /* and reset bit-buffer to empty */
- state->cur.put_bits = 0;
- return TRUE;
-}
-
-
-/* Encode a single block's worth of coefficients */
-
-LOCAL(boolean)
-encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val,
- c_derived_tbl *dctbl, c_derived_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] - last_dc_val;
-
- 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;
- }
- /* Check for out-of-range coefficient values.
- * Since we're encoding a difference, the range limit is twice as much.
- */
- if (nbits > MAX_COEF_BITS+1)
- ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
-
- /* Emit the Huffman-coded symbol for the number of bits */
- if (! emit_bits(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))
- return FALSE;
-
- /* 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 */
- if (! emit_bits(state, (unsigned int) temp2, nbits))
- return FALSE;
-
- /* 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) {
- if (! emit_bits(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0]))
- return FALSE;
- 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++;
- /* Check for out-of-range coefficient values */
- if (nbits > MAX_COEF_BITS)
- ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
-
- /* Emit Huffman symbol for run length / number of bits */
- i = (r << 4) + nbits;
- if (! emit_bits(state, actbl->ehufco[i], actbl->ehufsi[i]))
- return FALSE;
-
- /* Emit that number of bits of the value, if positive, */
- /* or the complement of its magnitude, if negative. */
- if (! emit_bits(state, (unsigned int) temp2, nbits))
- return FALSE;
-
- r = 0;
- }
- }
-
- /* If the last coef(s) were zero, emit an end-of-block code */
- if (r > 0)
- if (! emit_bits(state, actbl->ehufco[0], actbl->ehufsi[0]))
- return FALSE;
-
- return TRUE;
-}
-
-
-/*
- * Emit a restart marker & resynchronize predictions.
- */
-
-LOCAL(boolean)
-emit_restart (working_state * state, int restart_num)
-{
- int ci;
-
- if (! flush_bits(state))
- return FALSE;
-
- emit_byte(state, 0xFF, return FALSE);
- emit_byte(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;
-}
-
-
-/*
- * Encode and output one MCU's worth of Huffman-compressed coefficients.
- */
-
-METHODDEF(boolean)
-encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
-{
- huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
- working_state state;
- int blkn, ci;
- jpeg_component_info * compptr;
-
- /* Load up working state */
- state.next_output_byte = cinfo->dest->next_output_byte;
- state.free_in_buffer = cinfo->dest->free_in_buffer;
- ASSIGN_STATE(state.cur, entropy->saved);
- state.cinfo = cinfo;
-
- /* Emit restart marker if needed */
- if (cinfo->restart_interval) {
- if (entropy->restarts_to_go == 0)
- if (! emit_restart(&state, entropy->next_restart_num))
- return FALSE;
- }
-
- /* Encode the MCU data blocks */
- for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
- ci = cinfo->MCU_membership[blkn];
- compptr = cinfo->cur_comp_info[ci];
- if (! encode_one_block(&state,
- MCU_data[blkn][0], state.cur.last_dc_val[ci],
- entropy->dc_derived_tbls[compptr->dc_tbl_no],
- entropy->ac_derived_tbls[compptr->ac_tbl_no]))
- return FALSE;
- /* Update last_dc_val */
- state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
- }
-
- /* Completed MCU, so 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);
-
- /* Update restart-interval state too */
- if (cinfo->restart_interval) {
- if (entropy->restarts_to_go == 0) {
- entropy->restarts_to_go = cinfo->restart_interval;
- entropy->next_restart_num++;
- entropy->next_restart_num &= 7;
- }
- entropy->restarts_to_go--;
- }
-
- return TRUE;
-}
-
-
-/*
- * Finish up at the end of a Huffman-compressed scan.
- */
-
-METHODDEF(void)
-finish_pass_huff (j_compress_ptr cinfo)
-{
- huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
- working_state state;
-
- /* Load up working state ... flush_bits needs it */
- state.next_output_byte = cinfo->dest->next_output_byte;
- state.free_in_buffer = cinfo->dest->free_in_buffer;
- ASSIGN_STATE(state.cur, entropy->saved);
- state.cinfo = cinfo;
-
- /* 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.
- *
- * 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 a Huffman coding tree for the observed counts.
- * Symbols which are not needed at all for the particular image are not
- * assigned any code, which saves space in the DHT marker as well as in
- * the compressed data.
- */
-
-#ifdef ENTROPY_OPT_SUPPORTED
-
-
-/* Process a single block's worth of coefficients */
-
-LOCAL(void)
-htest_one_block (j_compress_ptr cinfo, 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;
- }
- /* Check for out-of-range coefficient values.
- * Since we're encoding a difference, the range limit is twice as much.
- */
- if (nbits > MAX_COEF_BITS+1)
- ERREXIT(cinfo, JERR_BAD_DCT_COEF);
-
- /* 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++;
- /* Check for out-of-range coefficient values */
- if (nbits > MAX_COEF_BITS)
- ERREXIT(cinfo, JERR_BAD_DCT_COEF);
-
- /* 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(cinfo, 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 best Huffman code table for the given counts, fill htbl.
- * Note this is also used by jcphuff.c.
- *
- * The JPEG standard requires that no symbol be assigned a codeword of all
- * one bits (so that padding bits added at the end of a compressed segment
- * can't look like a valid code). Because of the canonical ordering of
- * codewords, this just means that there must be an unused slot in the
- * longest codeword length category. Section K.2 of the JPEG spec suggests
- * reserving such a slot by pretending that symbol 256 is a valid symbol
- * with count 1. In theory that's not optimal; giving it count zero but
- * including it in the symbol set anyway should give a better Huffman code.
- * But the theoretically better code actually seems to come out worse in
- * practice, because it produces more all-ones bytes (which incur stuffed
- * zero bytes in the final file). In any case the difference is tiny.
- *
- * 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 JPEG section K.2. This method is *not*
- * optimal; it may not choose the best possible limited-length code. But
- * typically only very-low-frequency symbols will be given less-than-optimal
- * lengths, so the code is almost optimal. Experimental comparisons against
- * an optimal limited-length-code algorithm indicate that the difference is
- * microscopic --- usually less than a hundredth of a percent of total size.
- * So the extra complexity of an optimal algorithm doesn't seem worthwhile.
- */
-
-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 256 has 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 last 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
- }
-}
projects / opencv / blobdiff