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 /** Structure for bistream I/O. */
13 struct getbit_context
{
14 /* Start of the internal buffer. */
15 const uint8_t *buffer
;
16 /* End of the internal buffer. */
17 const uint8_t *buffer_end
;
22 #define VLC_TYPE int16_t
26 VLC_TYPE(*table
)[2]; ///< code, bits
27 int table_size
, table_allocated
;
30 static inline uint32_t show_bits(struct getbit_context
*gbc
, int num
)
33 const uint8_t *p
= gbc
->buffer
+ (idx
>> 3);
34 uint32_t x
= ((p
[0] << 24) | (p
[1] << 16) | (p
[2] << 8) | p
[3]);
35 return (x
<< (idx
& 7)) >> (32 - num
);
38 static inline int get_bits_count(struct getbit_context
*gbc
)
43 static inline void skip_bits(struct getbit_context
*gbc
, int n
)
48 static inline unsigned int get_bits(struct getbit_context
*gbc
, int n
)
50 unsigned int ret
= show_bits(gbc
, n
);
55 /* This is rather hot, we can do better than get_bits(gbc, 1). */
56 static inline unsigned int get_bit(struct getbit_context
*gbc
)
58 int idx
= gbc
->index
++;
59 uint8_t tmp
= gbc
->buffer
[idx
>> 3], mask
= (1 << (7 - (idx
& 7)));
60 return !!(tmp
& mask
);
64 * Initialize a getbit_context structure.
66 * \param buffer The bitstream buffer. It must be FF_INPUT_BUFFER_PADDING_SIZE
67 * bytes larger then the actual read bits * because some optimized bitstream
68 * readers read 32 or 64 bit at once and could read over the end.
70 * \param bit_size The size of the buffer in bytes.
72 static inline void init_get_bits(struct getbit_context
*gbc
,
73 const uint8_t *buffer
, int size
)
76 gbc
->buffer_end
= buffer
+ size
;
80 void init_vlc(struct vlc
*vlc
, int nb_bits
, int nb_codes
, const void *bits
,
81 const void *codes
, int codes_size
);
83 void free_vlc(struct vlc
*vlc
);
88 * \param bits The number of bits which will be read at once, must be
89 * identical to nb_bits in init_vlc()
91 * \param max_depth The number of times bits bits must be read to completely
92 * read the longest vlc code = (max_vlc_length + bits - 1) / bits.
94 static inline int get_vlc(struct getbit_context
*gbc
, VLC_TYPE(*table
)[2],
95 int bits
, int max_depth
)
97 int n
, idx
, nb_bits
, code
;
99 idx
= show_bits(gbc
, bits
);
100 code
= table
[idx
][0];
102 if (max_depth
> 1 && n
< 0) {
103 skip_bits(gbc
, bits
);
105 idx
= show_bits(gbc
, nb_bits
) + code
;
106 code
= table
[idx
][0];
108 if (max_depth
> 2 && n
< 0) {
109 skip_bits(gbc
, nb_bits
);
111 idx
= show_bits(gbc
, nb_bits
) + code
;
112 code
= table
[idx
][0];