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