274 lines
7.7 KiB
C
274 lines
7.7 KiB
C
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/*
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* Common bit i/o utils
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* Copyright (c) 2000, 2001 Fabrice Bellard.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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* Modified by Matt Campbell <mattcampbell@pobox.com> for the stand-alone
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* mpaudec library. Based on common.c from libavcodec.
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*/
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#include "internal.h"
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/**
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* init GetBitContext.
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* @param buffer bitstream buffer
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* @param bit_size the size of the buffer in bits
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*/
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void init_get_bits(GetBitContext *s,
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const uint8_t *buffer, int bit_size)
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{
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s->buffer= buffer;
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s->size_in_bits= bit_size;
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s->index=0;
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}
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unsigned int show_bits(const GetBitContext *s, int n)
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{
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int i;
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unsigned int result = 0;
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assert(s->size_in_bits - s->index >= n);
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for (i = s->index; i < s->index + n; i++) {
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int byte_index = i / 8;
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unsigned int right_shift = 7 - (i % 8);
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uint8_t byte = s->buffer[byte_index];
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uint8_t bit;
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result <<= 1;
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if (right_shift == 0)
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bit = byte & 0x1;
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else
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bit = (byte >> right_shift) & 0x1;
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result |= (unsigned int)bit;
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}
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return result;
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}
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void skip_bits(GetBitContext *s, int n)
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{
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s->index += n;
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}
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unsigned int get_bits(GetBitContext *s, int n)
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{
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unsigned int result = show_bits(s, n);
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skip_bits(s, n);
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return result;
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}
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int get_bits_count(const GetBitContext *s)
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{
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return s->index;
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}
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/* VLC decoding */
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/*#define DEBUG_VLC*/
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#define GET_DATA(v, table, i, wrap, size) \
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{\
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const uint8_t *ptr = (const uint8_t *)table + i * wrap;\
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switch(size) {\
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case 1:\
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v = *(const uint8_t *)ptr;\
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break;\
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case 2:\
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v = *(const uint16_t *)ptr;\
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break;\
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default:\
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v = *(const uint32_t *)ptr;\
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break;\
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}\
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}
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static int alloc_table(VLC *vlc, int size)
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{
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int index;
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index = vlc->table_size;
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vlc->table_size += size;
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if (vlc->table_size > vlc->table_allocated) {
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vlc->table_allocated += (1 << vlc->bits);
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vlc->table = realloc(vlc->table,
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sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
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if (!vlc->table)
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return -1;
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}
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return index;
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}
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static int build_table(VLC *vlc, int table_nb_bits,
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int nb_codes,
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const void *bits, int bits_wrap, int bits_size,
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const void *codes, int codes_wrap, int codes_size,
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uint32_t code_prefix, int n_prefix)
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{
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int i, j, k, n, table_size, table_index, nb, n1, index;
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uint32_t code;
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VLC_TYPE (*table)[2];
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table_size = 1 << table_nb_bits;
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table_index = alloc_table(vlc, table_size);
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#ifdef DEBUG_VLC
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printf("new table index=%d size=%d code_prefix=%x n=%d\n",
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table_index, table_size, code_prefix, n_prefix);
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#endif
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if (table_index < 0)
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return -1;
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table = &vlc->table[table_index];
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for(i=0;i<table_size;i++) {
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table[i][1] = 0; /*bits*/
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table[i][0] = -1; /*codes*/
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}
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/* first pass: map codes and compute auxillary table sizes */
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for(i=0;i<nb_codes;i++) {
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GET_DATA(n, bits, i, bits_wrap, bits_size);
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GET_DATA(code, codes, i, codes_wrap, codes_size);
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/* we accept tables with holes */
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if (n <= 0)
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continue;
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#if defined(DEBUG_VLC) && 0
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printf("i=%d n=%d code=0x%x\n", i, n, code);
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#endif
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/* if code matches the prefix, it is in the table */
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n -= n_prefix;
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if (n > 0 && (code >> n) == code_prefix) {
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if (n <= table_nb_bits) {
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/* no need to add another table */
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j = (code << (table_nb_bits - n)) & (table_size - 1);
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nb = 1 << (table_nb_bits - n);
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for(k=0;k<nb;k++) {
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#ifdef DEBUG_VLC
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printf("%4x: code=%d n=%d\n",
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j, i, n);
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#endif
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assert(table[j][1] /*bits*/ == 0);
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table[j][1] = n; /*bits*/
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table[j][0] = i; /*code*/
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j++;
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}
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} else {
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n -= table_nb_bits;
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j = (code >> n) & ((1 << table_nb_bits) - 1);
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#ifdef DEBUG_VLC
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printf("%4x: n=%d (subtable)\n",
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j, n);
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#endif
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/* compute table size */
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n1 = -table[j][1]; /*bits*/
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if (n > n1)
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n1 = n;
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table[j][1] = -n1; /*bits*/
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}
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}
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}
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/* second pass : fill auxillary tables recursively */
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for(i=0;i<table_size;i++) {
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n = table[i][1]; /*bits*/
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if (n < 0) {
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n = -n;
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if (n > table_nb_bits) {
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n = table_nb_bits;
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table[i][1] = -n; /*bits*/
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}
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index = build_table(vlc, n, nb_codes,
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bits, bits_wrap, bits_size,
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codes, codes_wrap, codes_size,
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(code_prefix << table_nb_bits) | i,
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n_prefix + table_nb_bits);
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if (index < 0)
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return -1;
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/* note: realloc has been done, so reload tables */
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table = &vlc->table[table_index];
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table[i][0] = index; /*code*/
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}
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}
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return table_index;
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}
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/* Build VLC decoding tables suitable for use with get_vlc().
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'nb_bits' set thee decoding table size (2^nb_bits) entries. The
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bigger it is, the faster is the decoding. But it should not be too
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big to save memory and L1 cache. '9' is a good compromise.
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'nb_codes' : number of vlcs codes
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'bits' : table which gives the size (in bits) of each vlc code.
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'codes' : table which gives the bit pattern of of each vlc code.
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'xxx_wrap' : give the number of bytes between each entry of the
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'bits' or 'codes' tables.
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'xxx_size' : gives the number of bytes of each entry of the 'bits'
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or 'codes' tables.
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'wrap' and 'size' allows to use any memory configuration and types
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(byte/word/long) to store the 'bits' and 'codes' tables.
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*/
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int init_vlc(VLC *vlc, int nb_bits, int nb_codes,
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const void *bits, int bits_wrap, int bits_size,
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const void *codes, int codes_wrap, int codes_size)
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{
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vlc->bits = nb_bits;
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vlc->table = NULL;
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vlc->table_allocated = 0;
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vlc->table_size = 0;
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#ifdef DEBUG_VLC
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printf("build table nb_codes=%d\n", nb_codes);
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#endif
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if (build_table(vlc, nb_bits, nb_codes,
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bits, bits_wrap, bits_size,
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codes, codes_wrap, codes_size,
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0, 0) < 0) {
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free(vlc->table);
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return -1;
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}
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return 0;
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}
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void free_vlc(VLC *vlc)
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{
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free(vlc->table);
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}
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int get_vlc(GetBitContext *s, const VLC *vlc)
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{
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int code = 0;
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int depth = 0, max_depth = 3;
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int n, index, bits = vlc->bits;
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do {
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index = show_bits(s, bits) + code;
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code = vlc->table[index][0];
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n = vlc->table[index][1];
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depth++;
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if (n < 0 && depth < max_depth) {
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skip_bits(s, bits);
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bits = -n;
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}
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} while (n < 0 && depth < max_depth);
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skip_bits(s, n);
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return code;
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}
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