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, see file COPYING.LIB.
9 /** \file bitstream.h Bitstream structures and inline functions. */
11 /** Structure for bistream I/O. */
12 struct getbit_context
{
13 /** Start of the internal buffer. */
14 const uint8_t *buffer
;
15 /** Length of buffer in bits (always a multiple of 8). */
21 /** A variable length code table. */
23 /** Number of bits of the table. */
25 /** The code and the bits table. */
27 /** The size of the table. */
29 /** Amount of memory allocated so far. */
33 static inline uint32_t show_bits(struct getbit_context
*gbc
, int num
)
39 assert(idx
+ num
<= gbc
->num_bits
);
40 p
= (const char *)gbc
->buffer
+ (idx
>> 3);
42 return (x
<< (idx
& 7)) >> (32 - num
);
45 static inline int get_bits_count(struct getbit_context
*gbc
)
50 static inline void skip_bits(struct getbit_context
*gbc
, int n
)
52 assert(gbc
->index
+ n
<= gbc
->num_bits
);
56 static inline unsigned int get_bits(struct getbit_context
*gbc
, int n
)
58 unsigned int ret
= show_bits(gbc
, n
); /* checks n */
63 /* This is rather hot, we can do better than get_bits(gbc, 1). */
64 static inline unsigned int get_bit(struct getbit_context
*gbc
)
69 assert(gbc
->index
< gbc
->num_bits
);
71 tmp
= gbc
->buffer
[idx
>> 3];
72 mask
= 1 << (7 - (idx
& 7));
73 return !!(tmp
& mask
);
77 * Initialize a getbit_context structure.
79 * \param gbc The structure to initialize.
80 * \param buffer The bitstream buffer.
81 * \param size The size of the buffer in bytes.
83 * The bitstream buffer must be 4 bytes larger then the actual read bits
84 * because the bitstream reader might read 32 bits at once and could read over
87 static inline void init_get_bits(struct getbit_context
*gbc
,
88 const uint8_t *buffer
, int size
)
91 gbc
->num_bits
= size
* 8;
95 void init_vlc(struct vlc
*vlc
, int nb_bits
, int nb_codes
, const void *bits
,
96 const void *codes
, int codes_size
);
97 void free_vlc(struct vlc
*vlc
);
98 int get_vlc(struct getbit_context
*gbc
, const struct vlc
*vlc
);