2 * Extracted 2009 from mplayer 2009-02-10 libavcodec/bitstream.h.
4 * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
6 * Licensed under the GNU Lesser General Public License.
7 * For licencing details see COPYING.LIB.
10 /** \file bitstream.h Bitstream structures and inline functions. */
12 #define AV_RB32(x) ((((const uint8_t*)(x))[0] << 24) | \
13 (((const uint8_t*)(x))[1] << 16) | \
14 (((const uint8_t*)(x))[2] << 8) | \
15 ((const uint8_t*)(x))[3])
17 /** Structure for bistream I/O. */
18 struct getbit_context
{
19 /* Start of the internal buffer. */
20 const uint8_t *buffer
;
21 /* End of the internal buffer. */
22 const uint8_t *buffer_end
;
27 #define VLC_TYPE int16_t
31 VLC_TYPE(*table
)[2]; ///< code, bits
32 int table_size
, table_allocated
;
35 /** Load \a gb into local variables. */
36 #define OPEN_READER(name, gb)\
37 int name##_index= (gb)->index;\
40 /** Store local vars in gb. */
41 #define CLOSE_READER(name, gb)\
42 (gb)->index= name##_index;\
45 * Refill the internal cache from the bitstream.
47 #define UPDATE_CACHE(name, gb)\
48 name##_cache= AV_RB32( ((gb)->buffer) \
49 + (name##_index >> 3) ) << (name##_index & 0x07);\
52 * Remove the next num bits from the cache.
54 * SKIP_COUNTER MUST be called before UPDATE_CACHE / CLOSE_READER).
56 #define SKIP_CACHE(name, gb, num)\
57 name##_cache <<= (num);
60 * Increment the internal bit counter.
64 #define SKIP_COUNTER(name, gb, num)\
65 name##_index += (num);\
67 /** Return the next num bits. */
68 #define SHOW_UBITS(name, gb, num) \
69 (((uint32_t)(name##_cache)) >> (32 - (num)))
71 static inline int get_bits_count(struct getbit_context
*s
)
79 static inline unsigned int get_bits(struct getbit_context
*s
, int n
)
84 tmp
= SHOW_UBITS(re
, s
, n
);
85 SKIP_COUNTER(re
, s
, n
)
90 static inline void skip_bits(struct getbit_context
*s
, int n
)
95 static inline unsigned int get_bits1(struct getbit_context
*s
)
98 uint8_t result
= s
->buffer
[idx
>> 3];
100 result
<<= (idx
& 0x07);
108 * Initialize a getbit_context structure.
110 * \param buffer The bitstream buffer. It must be FF_INPUT_BUFFER_PADDING_SIZE
111 * bytes larger then the actual read bits * because some optimized bitstream
112 * readers read 32 or 64 bit at once and could read over the end.
114 * \param bit_size The size of the buffer in bytes.
116 static inline void init_get_bits(struct getbit_context
*s
,
117 const uint8_t *buffer
, int size
)
120 s
->buffer_end
= buffer
+ size
;
124 void init_vlc(struct vlc
*vlc
, int nb_bits
, int nb_codes
, const void *bits
,
125 const void *codes
, int codes_size
);
127 void free_vlc(struct vlc
*vlc
);
132 * \param bits The number of bits which will be read at once, must be
133 * identical to nb_bits in init_vlc()
135 * \param max_depth The number of times bits bits must be read to completely
136 * read the longest vlc code = (max_vlc_length + bits - 1) / bits.
138 static inline int get_vlc(struct getbit_context
*gb
, VLC_TYPE(*table
)[2],
139 int bits
, int max_depth
)
141 int n
, idx
, nb_bits
, code
;
145 idx
= SHOW_UBITS(re
, gb
, bits
);
146 code
= table
[idx
][0];
148 if (max_depth
> 1 && n
< 0) {
149 SKIP_COUNTER(re
, gb
, bits
)
152 idx
= SHOW_UBITS(re
, gb
, nb_bits
) + code
;
153 code
= table
[idx
][0];
155 if (max_depth
> 2 && n
< 0) {
156 SKIP_COUNTER(re
, gb
, nb_bits
)
159 idx
= SHOW_UBITS(re
, gb
, nb_bits
) + code
;
160 code
= table
[idx
][0];
164 SKIP_CACHE(re
, gb
, n
)
165 SKIP_COUNTER(re
, gb
, n
)