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 /** Read an 8, 16, or 32 bit entity from a VLC table. */
  31 #define GET_DATA(v, table, i, size) \
  32 {\
  33         const uint8_t *ptr = (const uint8_t *)table + i * size; \
  34         switch (size) { \
  35         case 1: \
  36                 v = *(const uint8_t *)ptr; \
  37                 break; \
  38         case 2: \
  39                 v = *(const uint16_t *)ptr; \
  40                 break; \
  41         default: \
  42                 v = *(const uint32_t *)ptr; \
  43                 break; \
  44         } \
  45 }
  46
  47 static void alloc_table(struct vlc *vlc, int size)
  48 {
  49         vlc->table_size += size;
  50         if (vlc->table_size > vlc->table_allocated) {
  51                 vlc->table_allocated += (1 << vlc->bits);
  52                 vlc->table = para_realloc(vlc->table,
  53                         sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
  54         }
  55 }
  56
  57 static int build_table(struct vlc *vlc, int table_nb_bits, int nb_codes,
  58                 const void *bits, const void *codes, int codes_size,
  59                 uint32_t code_prefix, int n_prefix)
  60 {
  61         int i, j, k, n, table_size, table_index, nb, n1, idx, code_prefix2,
  62                 symbol;
  63         uint32_t code;
  64         VLC_TYPE(*table)[2];
  65
  66         table_size = 1 << table_nb_bits;
  67         table_index = vlc->table_size;
  68         alloc_table(vlc, table_size);
  69         table = &vlc->table[table_index];
  70
  71         for (i = 0; i < table_size; i++) {
  72                 table[i][1] = 0;        //bits
  73                 table[i][0] = -1;       //codes
  74         }
  75
  76         /* map codes and compute auxillary table sizes */
  77         for (i = 0; i < nb_codes; i++) {
  78                 GET_DATA(n, bits, i, 1);
  79                 GET_DATA(code, codes, i, codes_size);
  80                 /* we accept tables with holes */
  81                 if (n <= 0)
  82                         continue;
  83                 symbol = i;
  84                 /* if code matches the prefix, it is in the table */
  85                 n -= n_prefix;
  86                 code_prefix2 = code >> n;
  87                 if (n <= 0 || code_prefix2 != code_prefix)
  88                         continue;
  89                 if (n <= table_nb_bits) {
  90                         /* no need to add another table */
  91                         j = (code << (table_nb_bits - n)) & (table_size - 1);
  92                         nb = 1 << (table_nb_bits - n);
  93                         for (k = 0; k < nb; k++) {
  94                                 if (table[j][1] /* bits */ != 0) {
  95                                         PARA_EMERG_LOG("incorrect code\n");
  96                                         exit(EXIT_FAILURE);
  97                                 }
  98                                 table[j][1] = n;        //bits
  99                                 table[j][0] = symbol;
 100                                 j++;
 101                         }
 102                 } else {
 103                         n -= table_nb_bits;
 104                         j = (code >> n) & ((1 << table_nb_bits) - 1);
 105                         /* compute table size */
 106                         n1 = -table[j][1];      //bits
 107                         if (n > n1)
 108                                 n1 = n;
 109                         table[j][1] = -n1;      //bits
 110                 }
 111         }
 112
 113         /* fill auxillary tables recursively */
 114         for (i = 0; i < table_size; i++) {
 115                 n = table[i][1];        //bits
 116                 if (n < 0) {
 117                         n = -n;
 118                         if (n > table_nb_bits) {
 119                                 n = table_nb_bits;
 120                                 table[i][1] = -n;       //bits
 121                         }
 122                         idx = build_table(vlc, n, nb_codes, bits, codes,
 123                                 codes_size, (code_prefix << table_nb_bits) | i,
 124                                 n_prefix + table_nb_bits);
 125                         /* vlc->table might have changed */
 126                         table = &vlc->table[table_index];
 127                         table[i][0] = idx;      //code
 128                 }
 129         }
 130         return table_index;
 131 }
 132
 133 /**
 134  * Build VLC decoding tables suitable for use with get_vlc().
 135  *
 136  * \param vlc The structure to be initialized.
 137  *
 138  * \param nb_bits Set the decoding table size (2^nb_bits) entries. The bigger
 139  * it is, the faster is the decoding. But it should not be too big to save
 140  * memory and L1 cache. '9' is a good compromise.
 141  *
 142  * \param nb_codes Number of vlcs codes.
 143  *
 144  * \param bits Table which gives the size (in bits) of each vlc code.
 145  *
 146  * \param codes Table which gives the bit pattern of of each vlc code.
 147  *
 148  * \param codes_size The number of bytes of each entry of the \a codes tables.
 149  *
 150  * The wrap and size parameters allow to use any memory configuration and
 151  * types (byte/word/long) to store the bits and codes tables.
 152  */
 153 void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
 154                 const void *codes, int codes_size)
 155 {
 156         PARA_INFO_LOG("nb_codes: %d\n", nb_codes);
 157         vlc->bits = nb_bits;
 158         vlc->table = NULL;
 159         vlc->table_allocated = 0;
 160         vlc->table_size = 0;
 161         build_table(vlc, nb_bits, nb_codes, bits, codes, codes_size, 0, 0);
 162 }
 163
 164 /**
 165  * Deallocate all resources of a VLC table.
 166  *
 167  * \param vlc Pointer to an initialized vlc structure.
 168  *
 169  * The table given by \a vlc must have been initialized earlier via \ref
 170  * init_vlc().
 171  */
 172 void free_vlc(struct vlc *vlc)
 173 {
 174         freep(&vlc->table);
 175 }
 176
 177 /**
 178  * Parse a vlc code.
 179  *
 180  * \param gbc The getbit context structure.
 181  *
 182  * \param table The vlc tables to use.
 183  *
 184  * \param bits The number of bits which will be read at once, must be
 185  * identical to nb_bits in init_vlc().
 186  *
 187  * \param max_depth The number of times bits bits must be read to completely
 188  * read the longest vlc code = (max_vlc_length + bits - 1) / bits.
 189  *
 190  * \return The vlc code.
 191  */
 192 int get_vlc(struct getbit_context *gbc, VLC_TYPE(*table)[2], int bits,
 193                 int max_depth)
 194 {
 195         int n, idx, nb_bits, code;
 196
 197         idx = show_bits(gbc, bits);
 198         code = table[idx][0];
 199         n = table[idx][1];
 200         if (max_depth > 1 && n < 0) {
 201                 skip_bits(gbc, bits);
 202                 nb_bits = -n;
 203                 idx = show_bits(gbc, nb_bits) + code;
 204                 code = table[idx][0];
 205                 n = table[idx][1];
 206                 if (max_depth > 2 && n < 0) {
 207                         skip_bits(gbc, nb_bits);
 208                         nb_bits = -n;
 209                         idx = show_bits(gbc, nb_bits) + code;
 210                         code = table[idx][0];
 211                         n = table[idx][1];
 212                 }
 213         }
 214         skip_bits(gbc, n);
 215         return code >= 0? code : -E_VLC;
 216 }