2 * Common bit I/O utils.
4 * Extracted 2009 from mplayer 2009-02-10 libavcodec/bitstream.c.
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>
10 * Licensed under the GNU Lesser General Public License.
11 * For licencing details see COPYING.LIB.
15 * \file bitstream.c Bitstream API.
28 #include "bitstream.h"
30 /** Read an 8, 16, or 32 bit entity from a VLC table. */
31 #define GET_DATA(v, table, i, size) \
33 const uint8_t *ptr = (const uint8_t *)table + i * size; \
36 v = *(const uint8_t *)ptr; \
39 v = *(const uint16_t *)ptr; \
42 v = *(const uint32_t *)ptr; \
47 static void alloc_table(struct vlc *vlc, int size)
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);
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)
61 int i, j, k, n, table_size, table_index, nb, n1, idx, code_prefix2,
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];
71 for (i = 0; i < table_size; i++) {
72 table[i][1] = 0; //bits
73 table[i][0] = -1; //codes
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 */
84 /* if code matches the prefix, it is in the table */
86 code_prefix2 = code >> n;
87 if (n <= 0 || code_prefix2 != code_prefix)
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");
98 table[j][1] = n; //bits
104 j = (code >> n) & ((1 << table_nb_bits) - 1);
105 /* compute table size */
106 n1 = -table[j][1]; //bits
109 table[j][1] = -n1; //bits
113 /* fill auxillary tables recursively */
114 for (i = 0; i < table_size; i++) {
115 n = table[i][1]; //bits
118 if (n > table_nb_bits) {
120 table[i][1] = -n; //bits
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
134 * Build VLC decoding tables suitable for use with get_vlc().
136 * \param vlc The structure to be initialized.
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.
142 * \param nb_codes Number of vlcs codes.
144 * \param bits Table which gives the size (in bits) of each vlc code.
146 * \param codes Table which gives the bit pattern of of each vlc code.
148 * \param codes_size The number of bytes of each entry of the \a codes tables.
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.
153 void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
154 const void *codes, int codes_size)
156 PARA_INFO_LOG("nb_codes: %d\n", nb_codes);
159 vlc->table_allocated = 0;
161 build_table(vlc, nb_bits, nb_codes, bits, codes, codes_size, 0, 0);
165 * Deallocate all resources of a VLC table.
167 * \param vlc Pointer to an initialized vlc structure.
169 * The table given by \a vlc must have been initialized earlier via \ref
172 void free_vlc(struct vlc *vlc)
180 * \param gbc The getbit context structure.
182 * \param table The vlc tables to use.
184 * \param bits The number of bits which will be read at once, must be
185 * identical to nb_bits in init_vlc().
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.
190 * \return The vlc code.
192 int get_vlc(struct getbit_context *gbc, VLC_TYPE(*table)[2], int bits,
195 int n, idx, nb_bits, code;
197 idx = show_bits(gbc, bits);
198 code = table[idx][0];
200 if (max_depth > 1 && n < 0) {
201 skip_bits(gbc, bits);
203 idx = show_bits(gbc, nb_bits) + code;
204 code = table[idx][0];
206 if (max_depth > 2 && n < 0) {
207 skip_bits(gbc, nb_bits);
209 idx = show_bits(gbc, nb_bits) + code;
210 code = table[idx][0];
215 return code >= 0? code : -E_VLC;