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Diffstat (limited to 'src/jpeg-6b/jchuff.c')
| -rw-r--r-- | src/jpeg-6b/jchuff.c | 909 |
1 files changed, 0 insertions, 909 deletions
diff --git a/src/jpeg-6b/jchuff.c b/src/jpeg-6b/jchuff.c deleted file mode 100644 index f2352505..00000000 --- a/src/jpeg-6b/jchuff.c +++ /dev/null @@ -1,909 +0,0 @@ -/* - * 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 - } -} |