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