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 #define NEG_USR32(a,s) (((uint32_t)(a))>>(32-(s)))
19 /** Structure for bistream I/O. */
20 struct getbit_context {
21 /* Start of the internal buffer. */
22 const uint8_t *buffer;
23 /* End of the internal buffer. */
24 const uint8_t *buffer_end;
29 #define VLC_TYPE int16_t
33 VLC_TYPE(*table)[2]; ///< code, bits
34 int table_size, table_allocated;
37 /** Load \a gb into local variables. */
38 #define OPEN_READER(name, gb)\
39 int name##_index= (gb)->index;\
42 /** Store local vars in gb. */
43 #define CLOSE_READER(name, gb)\
44 (gb)->index= name##_index;\
47 * Refill the internal cache from the bitstream.
49 #define UPDATE_CACHE(name, gb)\
50 name##_cache= AV_RB32( ((gb)->buffer) \
51 + (name##_index >> 3) ) << (name##_index & 0x07);\
54 * Remove the next num bits from the cache.
56 * SKIP_COUNTER MUST be called before UPDATE_CACHE / CLOSE_READER).
58 #define SKIP_CACHE(name, gb, num)\
59 name##_cache <<= (num);
62 * Increment the internal bit counter.
64 * \sa SKIP_CACHE, SKIP_BITS.
66 #define SKIP_COUNTER(name, gb, num)\
67 name##_index += (num);\
70 * Skip over the next num bits.
72 * This is equivalent to SKIP_CACHE; SKIP_COUNTER.
74 #define SKIP_BITS(name, gb, num)\
76 SKIP_CACHE(name, gb, num)\
77 SKIP_COUNTER(name, gb, num)\
80 /** Return the next num bits. */
81 #define SHOW_UBITS(name, gb, num)\
82 NEG_USR32(name##_cache, num)
84 static inline int get_bits_count(struct getbit_context *s)
92 static inline unsigned int get_bits(struct getbit_context *s, int n)
97 tmp = SHOW_UBITS(re, s, n);
98 SKIP_COUNTER(re, s, n)
103 static inline void skip_bits(struct getbit_context *s, int n)
105 /* gcc seems to optimize this to s->index+=n for the ALT_READER :)) */
108 SKIP_COUNTER(re, s, n)
112 static inline unsigned int get_bits1(struct getbit_context *s)
115 uint8_t result = s->buffer[idx >> 3];
117 result <<= (idx & 0x07);
125 * Initialize a getbit_context structure.
127 * \param buffer The bitstream buffer. It must be FF_INPUT_BUFFER_PADDING_SIZE
128 * bytes larger then the actual read bits * because some optimized bitstream
129 * readers read 32 or 64 bit at once and could read over the end.
131 * \param bit_size The size of the buffer in bytes.
133 static inline void init_get_bits(struct getbit_context *s,
134 const uint8_t *buffer, int size)
137 s->buffer_end = buffer + size;
141 void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
142 const void *codes, int codes_size);
144 void free_vlc(struct vlc *vlc);
149 * \param bits The number of bits which will be read at once, must be
150 * identical to nb_bits in init_vlc()
152 * \param max_depth The number of times bits bits must be read to completely
153 * read the longest vlc code = (max_vlc_length + bits - 1) / bits.
155 static inline int get_vlc(struct getbit_context *gb, VLC_TYPE(*table)[2],
156 int bits, int max_depth)
158 int n, idx, nb_bits, code;
162 idx = SHOW_UBITS(re, gb, bits);
163 code = table[idx][0];
165 if (max_depth > 1 && n < 0) {
166 SKIP_COUNTER(re, gb, bits)
169 idx = SHOW_UBITS(re, gb, nb_bits) + code;
170 code = table[idx][0];
172 if (max_depth > 2 && n < 0) {
173 SKIP_COUNTER(re, gb, nb_bits)
176 idx = SHOW_UBITS(re, gb, nb_bits) + code;
177 code = table[idx][0];