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