bitstream.c

   1 /*
   2  * Common bit I/O utils.
   3  *
   4  * Extracted 2009 from mplayer 2009-02-10 libavcodec/bitstream.c.
   5  *
   6  * Copyright (c) 2000, 2001 Fabrice Bellard
   7  * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
   8  * alternative bitstream reader & writer by Michael Niedermayer <michaelni@gmx.at>
   9  *
  10  * Licensed under the GNU Lesser General Public License.
  11  * For licencing details see COPYING.LIB.
  12  */
  13
  14 /**
  15  * \file bitstream.c Bitstream API.
  16  */
  17
  18 #include <stdlib.h>
  19 #include <inttypes.h>
  20 #include <stdio.h>
  21 #include <string.h>
  22 #include <regex.h>
  23
  24 #include "para.h"
  25 #include "error.h"
  26 #include "string.h"
  27 #include "wma.h"
  28 #include "bitstream.h"
  29
  30 #define GET_DATA(v, table, i, size) \
  31 {\
  32         const uint8_t *ptr = (const uint8_t *)table + i * size; \
  33         switch (size) { \
  34         case 1: \
  35                 v = *(const uint8_t *)ptr; \
  36                 break; \
  37         case 2: \
  38                 v = *(const uint16_t *)ptr; \
  39                 break; \
  40         default: \
  41                 v = *(const uint32_t *)ptr; \
  42                 break; \
  43         } \
  44 }
  45
  46 static void alloc_table(struct vlc *vlc, int size)
  47 {
  48         vlc->table_size += size;
  49         if (vlc->table_size > vlc->table_allocated) {
  50                 vlc->table_allocated += (1 << vlc->bits);
  51                 vlc->table = para_realloc(vlc->table,
  52                         sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
  53         }
  54 }
  55
  56 static int build_table(struct vlc *vlc, int table_nb_bits, int nb_codes,
  57                 const void *bits, const void *codes, int codes_size,
  58                 uint32_t code_prefix, int n_prefix)
  59 {
  60         int i, j, k, n, table_size, table_index, nb, n1, idx, code_prefix2,
  61                 symbol;
  62         uint32_t code;
  63         VLC_TYPE(*table)[2];
  64
  65         table_size = 1 << table_nb_bits;
  66         table_index = vlc->table_size;
  67         alloc_table(vlc, table_size);
  68         table = &vlc->table[table_index];
  69
  70         for (i = 0; i < table_size; i++) {
  71                 table[i][1] = 0;        //bits
  72                 table[i][0] = -1;       //codes
  73         }
  74
  75         /* map codes and compute auxillary table sizes */
  76         for (i = 0; i < nb_codes; i++) {
  77                 GET_DATA(n, bits, i, 1);
  78                 GET_DATA(code, codes, i, codes_size);
  79                 /* we accept tables with holes */
  80                 if (n <= 0)
  81                         continue;
  82                 symbol = i;
  83                 /* if code matches the prefix, it is in the table */
  84                 n -= n_prefix;
  85                 code_prefix2 = code >> n;
  86                 if (n <= 0 || code_prefix2 != code_prefix)
  87                         continue;
  88                 if (n <= table_nb_bits) {
  89                         /* no need to add another table */
  90                         j = (code << (table_nb_bits - n)) & (table_size - 1);
  91                         nb = 1 << (table_nb_bits - n);
  92                         for (k = 0; k < nb; k++) {
  93                                 if (table[j][1] /* bits */ != 0) {
  94                                         PARA_EMERG_LOG("incorrect code\n");
  95                                         exit(EXIT_FAILURE);
  96                                 }
  97                                 table[j][1] = n;        //bits
  98                                 table[j][0] = symbol;
  99                                 j++;
 100                         }
 101                 } else {
 102                         n -= table_nb_bits;
 103                         j = (code >> n) & ((1 << table_nb_bits) - 1);
 104                         /* compute table size */
 105                         n1 = -table[j][1];      //bits
 106                         if (n > n1)
 107                                 n1 = n;
 108                         table[j][1] = -n1;      //bits
 109                 }
 110         }
 111
 112         /* fill auxillary tables recursively */
 113         for (i = 0; i < table_size; i++) {
 114                 n = table[i][1];        //bits
 115                 if (n < 0) {
 116                         n = -n;
 117                         if (n > table_nb_bits) {
 118                                 n = table_nb_bits;
 119                                 table[i][1] = -n;       //bits
 120                         }
 121                         idx = build_table(vlc, n, nb_codes, bits, codes,
 122                                 codes_size, (code_prefix << table_nb_bits) | i,
 123                                 n_prefix + table_nb_bits);
 124                         /* vlc->table might have changed */
 125                         table = &vlc->table[table_index];
 126                         table[i][0] = idx;      //code
 127                 }
 128         }
 129         return table_index;
 130 }
 131
 132 /**
 133  * Build VLC decoding tables suitable for use with get_vlc().
 134  *
 135  * \param vlc The structure to be initialized.
 136  *
 137  * \param nb_bits Set the decoding table size (2^nb_bits) entries. The bigger
 138  * it is, the faster is the decoding. But it should not be too big to save
 139  * memory and L1 cache. '9' is a good compromise.
 140  *
 141  * \param nb_codes Number of vlcs codes.
 142  *
 143  * \param bits Table which gives the size (in bits) of each vlc code.
 144  *
 145  * \param codes Table which gives the bit pattern of of each vlc code.
 146  *
 147  * \param codes_size The number of bytes of each entry of the \a codes tables.
 148  *
 149  * The wrap and size parameters allow to use any memory configuration and
 150  * types (byte/word/long) to store the bits and codes tables.
 151  */
 152 void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
 153                 const void *codes, int codes_size)
 154 {
 155         PARA_INFO_LOG("nb_codes: %d\n", nb_codes);
 156         vlc->bits = nb_bits;
 157         vlc->table = NULL;
 158         vlc->table_allocated = 0;
 159         vlc->table_size = 0;
 160         build_table(vlc, nb_bits, nb_codes, bits, codes, codes_size, 0, 0);
 161 }
 162
 163 void free_vlc(struct vlc *vlc)
 164 {
 165         freep(&vlc->table);
 166 }
 167
 168 /**
 169  * Parse a vlc code.
 170  *
 171  * \param gbc The getbit context structure.
 172  *
 173  * \param table The vlc tables to use.
 174  *
 175  * \param bits The number of bits which will be read at once, must be
 176  * identical to nb_bits in init_vlc().
 177  *
 178  * \param max_depth The number of times bits bits must be read to completely
 179  * read the longest vlc code = (max_vlc_length + bits - 1) / bits.
 180  *
 181  * \return The vlc code.
 182  */
 183 int get_vlc(struct getbit_context *gbc, VLC_TYPE(*table)[2], int bits,
 184                 int max_depth)
 185 {
 186         int n, idx, nb_bits, code;
 187
 188         idx = show_bits(gbc, bits);
 189         code = table[idx][0];
 190         n = table[idx][1];
 191         if (max_depth > 1 && n < 0) {
 192                 skip_bits(gbc, bits);
 193                 nb_bits = -n;
 194                 idx = show_bits(gbc, nb_bits) + code;
 195                 code = table[idx][0];
 196                 n = table[idx][1];
 197                 if (max_depth > 2 && n < 0) {
 198                         skip_bits(gbc, nb_bits);
 199                         nb_bits = -n;
 200                         idx = show_bits(gbc, nb_bits) + code;
 201                         code = table[idx][0];
 202                         n = table[idx][1];
 203                 }
 204         }
 205         skip_bits(gbc, n);
 206         return code >= 0? code : -E_VLC;
 207 }