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 #define GET_DATA(v, table, i, size) \
32 const uint8_t *ptr = (const uint8_t *)table + i * size; \
35 v = *(const uint8_t *)ptr; \
38 v = *(const uint16_t *)ptr; \
41 v = *(const uint32_t *)ptr; \
46 static void alloc_table(struct vlc
*vlc
, int size
)
48 vlc
->table_size
+= size
;
49 if (vlc
->table_size
> vlc
->table_allocated
) {
50 vlc
->table_allocated
+= (1 << vlc
->bits
);
51 vlc
->table
= para_realloc(vlc
->table
,
52 sizeof(VLC_TYPE
) * 2 * vlc
->table_allocated
);
56 static int build_table(struct vlc
*vlc
, int table_nb_bits
, int nb_codes
,
57 const void *bits
, const void *codes
, int codes_size
,
58 uint32_t code_prefix
, int n_prefix
)
60 int i
, j
, k
, n
, table_size
, table_index
, nb
, n1
, idx
, code_prefix2
,
65 table_size
= 1 << table_nb_bits
;
66 table_index
= vlc
->table_size
;
67 alloc_table(vlc
, table_size
);
68 table
= &vlc
->table
[table_index
];
70 for (i
= 0; i
< table_size
; i
++) {
71 table
[i
][1] = 0; //bits
72 table
[i
][0] = -1; //codes
75 /* map codes and compute auxillary table sizes */
76 for (i
= 0; i
< nb_codes
; i
++) {
77 GET_DATA(n
, bits
, i
, 1);
78 GET_DATA(code
, codes
, i
, codes_size
);
79 /* we accept tables with holes */
83 /* if code matches the prefix, it is in the table */
85 code_prefix2
= code
>> n
;
86 if (n
<= 0 || code_prefix2
!= code_prefix
)
88 if (n
<= table_nb_bits
) {
89 /* no need to add another table */
90 j
= (code
<< (table_nb_bits
- n
)) & (table_size
- 1);
91 nb
= 1 << (table_nb_bits
- n
);
92 for (k
= 0; k
< nb
; k
++) {
93 if (table
[j
][1] /* bits */ != 0) {
94 PARA_EMERG_LOG("incorrect code\n");
97 table
[j
][1] = n
; //bits
103 j
= (code
>> n
) & ((1 << table_nb_bits
) - 1);
104 /* compute table size */
105 n1
= -table
[j
][1]; //bits
108 table
[j
][1] = -n1
; //bits
112 /* fill auxillary tables recursively */
113 for (i
= 0; i
< table_size
; i
++) {
114 n
= table
[i
][1]; //bits
117 if (n
> table_nb_bits
) {
119 table
[i
][1] = -n
; //bits
121 idx
= build_table(vlc
, n
, nb_codes
, bits
, codes
,
122 codes_size
, (code_prefix
<< table_nb_bits
) | i
,
123 n_prefix
+ table_nb_bits
);
124 /* vlc->table might have changed */
125 table
= &vlc
->table
[table_index
];
126 table
[i
][0] = idx
; //code
133 * Build VLC decoding tables suitable for use with get_vlc().
135 * \param vlc The structure to be initialized.
137 * \param nb_bits Set the decoding table size (2^nb_bits) entries. The bigger
138 * it is, the faster is the decoding. But it should not be too big to save
139 * memory and L1 cache. '9' is a good compromise.
141 * \param nb_codes Number of vlcs codes.
143 * \param bits Table which gives the size (in bits) of each vlc code.
145 * \param codes Table which gives the bit pattern of of each vlc code.
147 * \param codes_size The number of bytes of each entry of the \a codes tables.
149 * The wrap and size parameters allow to use any memory configuration and
150 * types (byte/word/long) to store the bits and codes tables.
152 void init_vlc(struct vlc
*vlc
, int nb_bits
, int nb_codes
, const void *bits
,
153 const void *codes
, int codes_size
)
155 PARA_INFO_LOG("nb_codes: %d\n", nb_codes
);
158 vlc
->table_allocated
= 0;
160 build_table(vlc
, nb_bits
, nb_codes
, bits
, codes
, codes_size
, 0, 0);
163 void free_vlc(struct vlc
*vlc
)
171 * \param gbc The getbit context structure.
173 * \param table The vlc tables to use.
175 * \param bits The number of bits which will be read at once, must be
176 * identical to nb_bits in init_vlc().
178 * \param max_depth The number of times bits bits must be read to completely
179 * read the longest vlc code = (max_vlc_length + bits - 1) / bits.
181 * \return The vlc code.
183 int get_vlc(struct getbit_context
*gbc
, VLC_TYPE(*table
)[2], int bits
,
186 int n
, idx
, nb_bits
, code
;
188 idx
= show_bits(gbc
, bits
);
189 code
= table
[idx
][0];
191 if (max_depth
> 1 && n
< 0) {
192 skip_bits(gbc
, bits
);
194 idx
= show_bits(gbc
, nb_bits
) + code
;
195 code
= table
[idx
][0];
197 if (max_depth
> 2 && n
< 0) {
198 skip_bits(gbc
, nb_bits
);
200 idx
= show_bits(gbc
, nb_bits
) + code
;
201 code
= table
[idx
][0];
206 return code
>= 0? code
: -E_VLC
;