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  * Copyright (C) 2009 Andre Noll <maan@tuebingen.mpg.de>
  10  *
  11  * Licensed under the GNU Lesser General Public License. see file COPYING.LIB.
  12  */
  13
  14 /** \file bitstream.c Bitstream API for the wma decoder. */
  15
  16 #include <regex.h>
  17
  18 #include "para.h"
  19 #include "error.h"
  20 #include "string.h"
  21 #include "wma.h"
  22 #include "portable_io.h"
  23 #include "bitstream.h"
  24
  25 static inline uint32_t get_data(const void *table, int i, int size)
  26 {
  27         const uint8_t *ptr = (const uint8_t *)table + i * size;
  28         uint32_t v;
  29
  30         switch (size) {
  31         case 1:
  32                 v = *(const uint8_t *)ptr;
  33                 break;
  34         case 2:
  35                 v = *(const uint16_t *)ptr;
  36                 break;
  37         default:
  38                 v = *(const uint32_t *)ptr;
  39                 break;
  40         }
  41         return v;
  42 }
  43
  44 static void alloc_table(struct vlc *vlc, int size)
  45 {
  46         vlc->table_size += size;
  47         if (vlc->table_size > vlc->table_allocated) {
  48                 vlc->table_allocated += (1 << vlc->bits);
  49                 vlc->table = para_realloc(vlc->table,
  50                         sizeof(int16_t) * 2 * vlc->table_allocated);
  51         }
  52 }
  53
  54 static int build_table(struct vlc *vlc, int table_nb_bits, int nb_codes,
  55                 const void *bits, const void *codes, int codes_size,
  56                 uint32_t code_prefix, int n_prefix)
  57 {
  58         int i, j, k, n, table_size, table_index, nb, n1, idx;
  59         uint32_t code;
  60         int16_t (*table)[2];
  61
  62         table_size = 1 << table_nb_bits;
  63         table_index = vlc->table_size;
  64         alloc_table(vlc, table_size);
  65         table = &vlc->table[table_index];
  66
  67         for (i = 0; i < table_size; i++) {
  68                 table[i][1] = 0; /* bits */
  69                 table[i][0] = -1; /* codes */
  70         }
  71
  72         /* map codes and compute auxiliary table sizes */
  73         for (i = 0; i < nb_codes; i++) {
  74                 n = get_data(bits, i, 1);
  75                 /* we accept tables with holes */
  76                 n -= n_prefix;
  77                 if (n <= 0)
  78                         continue;
  79                 code = get_data(codes, i, codes_size);
  80                 /* if code matches the prefix, it is in the table */
  81                 if ((code >> n) != code_prefix)
  82                         continue;
  83                 if (n <= table_nb_bits) {
  84                         /* no need to add another table */
  85                         j = (code << (table_nb_bits - n)) & (table_size - 1);
  86                         nb = 1 << (table_nb_bits - n);
  87                         for (k = 0; k < nb; k++) {
  88                                 assert(table[j][1] == 0); /* incorrect code */
  89                                 table[j][1] = n; /* bits */
  90                                 table[j][0] = i;
  91                                 j++;
  92                         }
  93                 } else {
  94                         n -= table_nb_bits;
  95                         j = (code >> n) & ((1 << table_nb_bits) - 1);
  96                         /* compute table size */
  97                         n1 = -table[j][1]; /* bits */
  98                         if (n > n1)
  99                                 n1 = n;
 100                         table[j][1] = -n1; /* bits */
 101                 }
 102         }
 103
 104         /* fill auxiliary tables recursively */
 105         for (i = 0; i < table_size; i++) {
 106                 n = table[i][1]; /* bits */
 107                 if (n < 0) {
 108                         n = -n;
 109                         if (n > table_nb_bits) {
 110                                 n = table_nb_bits;
 111                                 table[i][1] = -n; /* bits */
 112                         }
 113                         idx = build_table(vlc, n, nb_codes, bits, codes,
 114                                 codes_size, (code_prefix << table_nb_bits) | i,
 115                                 n_prefix + table_nb_bits);
 116                         /* vlc->table might have changed */
 117                         table = &vlc->table[table_index];
 118                         table[i][0] = idx; /* code */
 119                 }
 120         }
 121         return table_index;
 122 }
 123
 124 /**
 125  * Build VLC decoding tables suitable for use with get_vlc().
 126  *
 127  * \param vlc The structure to be initialized.
 128  * \param nb_bits Set the decoding table size (2^nb_bits) entries.
 129  * \param nb_codes Number of vlc codes.
 130  * \param bits Table which gives the size (in bits) of each vlc code.
 131  * \param codes Table which gives the bit pattern of of each vlc code.
 132  * \param codes_size The number of bytes of each entry of the \a codes tables.
 133  *
 134  * The bigger \a nb_bits is, the faster is the decoding. But it should not be
 135  * too big to save memory and L1 cache. '9' is a good compromise.
 136  *
 137  * The wrap and size parameters allow to use any memory configuration and
 138  * types (byte/word/long) to store the bits and codes tables.
 139  */
 140 void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
 141                 const void *codes, int codes_size)
 142 {
 143         PARA_INFO_LOG("nb_codes: %d\n", nb_codes);
 144         vlc->bits = nb_bits;
 145         vlc->table = NULL;
 146         vlc->table_allocated = 0;
 147         vlc->table_size = 0;
 148         build_table(vlc, nb_bits, nb_codes, bits, codes, codes_size, 0, 0);
 149 }
 150
 151 /**
 152  * Deallocate all resources of a VLC table.
 153  *
 154  * \param vlc Pointer to an initialized vlc structure.
 155  *
 156  * The table given by \a vlc must have been initialized earlier via \ref
 157  * init_vlc().
 158  */
 159 void free_vlc(struct vlc *vlc)
 160 {
 161         freep(&vlc->table);
 162 }
 163
 164 /**
 165  * Parse a vlc code.
 166  *
 167  * \param gbc The getbit context structure.
 168  * \param vlc The vlc tables to use.
 169  *
 170  * \return The vlc code.
 171  */
 172 int get_vlc(struct getbit_context *gbc, const struct vlc *vlc)
 173 {
 174         int n, idx, nb_bits, code;
 175
 176         idx = show_bits(gbc, vlc->bits);
 177         code = vlc->table[idx][0];
 178         n = vlc->table[idx][1];
 179         if (n < 0) {
 180                 skip_bits(gbc, vlc->bits);
 181                 nb_bits = -n;
 182                 idx = show_bits(gbc, nb_bits) + code;
 183                 code = vlc->table[idx][0];
 184                 n = vlc->table[idx][1];
 185                 if (n < 0) {
 186                         skip_bits(gbc, nb_bits);
 187                         nb_bits = -n;
 188                         idx = show_bits(gbc, nb_bits) + code;
 189                         code = vlc->table[idx][0];
 190                         n = vlc->table[idx][1];
 191                 }
 192         }
 193         skip_bits(gbc, n);
 194         return code >= 0? code : -E_VLC;
 195 }