d052337c1a1825d29bc700c8a918177220dc4f74
[paraslash.git] / bitstream.h
1 /*
2 * Extracted 2009 from mplayer 2009-02-10 libavcodec/bitstream.h.
3 *
4 * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
5 *
6 * Licensed under the GNU Lesser General Public License.
7 * For licencing details see COPYING.LIB.
8 */
9
10 /** \file bitstream.h Bitstream structures and inline functions. */
11
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])
16
17 #define NEG_USR32(a,s) (((uint32_t)(a))>>(32-(s)))
18
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;
25 /** Bit counter. */
26 int index;
27 };
28
29 #define VLC_TYPE int16_t
30
31 struct vlc {
32 int bits;
33 VLC_TYPE(*table)[2]; ///< code, bits
34 int table_size, table_allocated;
35 };
36
37 /** Load \a gb into local variables. */
38 #define OPEN_READER(name, gb)\
39 int name##_index= (gb)->index;\
40 int name##_cache= 0;\
41
42 /** Store local vars in gb. */
43 #define CLOSE_READER(name, gb)\
44 (gb)->index= name##_index;\
45
46 /**
47 * Refill the internal cache from the bitstream.
48 */
49 #define UPDATE_CACHE(name, gb)\
50 name##_cache= AV_RB32( ((gb)->buffer) \
51 + (name##_index >> 3) ) << (name##_index & 0x07);\
52
53 /**
54 * Remove the next num bits from the cache.
55 *
56 * SKIP_COUNTER MUST be called before UPDATE_CACHE / CLOSE_READER).
57 */
58 #define SKIP_CACHE(name, gb, num)\
59 name##_cache <<= (num);
60
61 /**
62 * Increment the internal bit counter.
63 *
64 * \sa SKIP_CACHE, SKIP_BITS.
65 */
66 #define SKIP_COUNTER(name, gb, num)\
67 name##_index += (num);\
68
69 /**
70 * Skip over the next num bits.
71 *
72 * This is equivalent to SKIP_CACHE; SKIP_COUNTER.
73 */
74 #define SKIP_BITS(name, gb, num)\
75 {\
76 SKIP_CACHE(name, gb, num)\
77 SKIP_COUNTER(name, gb, num)\
78 }\
79
80 /** Return the next num bits. */
81 #define SHOW_UBITS(name, gb, num)\
82 NEG_USR32(name##_cache, num)
83
84 static inline int get_bits_count(struct getbit_context *s)
85 {
86 return s->index;
87 }
88
89 /**
90 * Read 1-17 bits.
91 */
92 static inline unsigned int get_bits(struct getbit_context *s, int n)
93 {
94 register int tmp;
95 OPEN_READER(re, s)
96 UPDATE_CACHE(re, s)
97 tmp = SHOW_UBITS(re, s, n);
98 SKIP_COUNTER(re, s, n)
99 CLOSE_READER(re, s)
100 return tmp;
101 }
102
103 static inline void skip_bits(struct getbit_context *s, int n)
104 {
105 /* gcc seems to optimize this to s->index+=n for the ALT_READER :)) */
106 OPEN_READER(re, s)
107 UPDATE_CACHE(re, s)
108 SKIP_COUNTER(re, s, n)
109 CLOSE_READER(re, s)
110 }
111
112 static inline unsigned int get_bits1(struct getbit_context *s)
113 {
114 int idx = s->index;
115 uint8_t result = s->buffer[idx >> 3];
116
117 result <<= (idx & 0x07);
118 result >>= 8 - 1;
119 idx++;
120 s->index = idx;
121 return result;
122 }
123
124 /**
125 * Initialize a getbit_context structure.
126 *
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.
130 *
131 * \param bit_size The size of the buffer in bytes.
132 */
133 static inline void init_get_bits(struct getbit_context *s,
134 const uint8_t *buffer, int size)
135 {
136 s->buffer = buffer;
137 s->buffer_end = buffer + size;
138 s->index = 0;
139 }
140
141 void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
142 const void *codes, int codes_size);
143
144 void free_vlc(struct vlc *vlc);
145
146 /**
147 * Parse a vlc code.
148 *
149 * \param bits The number of bits which will be read at once, must be
150 * identical to nb_bits in init_vlc()
151 *
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.
154 */
155 static inline int get_vlc(struct getbit_context *gb, VLC_TYPE(*table)[2],
156 int bits, int max_depth)
157 {
158 int n, idx, nb_bits, code;
159
160 OPEN_READER(re, gb)
161 UPDATE_CACHE(re, gb)
162 idx = SHOW_UBITS(re, gb, bits);
163 code = table[idx][0];
164 n = table[idx][1];
165 if (max_depth > 1 && n < 0) {
166 SKIP_COUNTER(re, gb, bits)
167 UPDATE_CACHE(re, gb)
168 nb_bits = -n;
169 idx = SHOW_UBITS(re, gb, nb_bits) + code;
170 code = table[idx][0];
171 n = table[idx][1];
172 if (max_depth > 2 && n < 0) {
173 SKIP_COUNTER(re, gb, nb_bits)
174 UPDATE_CACHE(re, gb)
175 nb_bits = -n;
176 idx = SHOW_UBITS(re, gb, nb_bits) + code;
177 code = table[idx][0];
178 n = table[idx][1];
179 }
180 }
181 SKIP_BITS(re, gb, n)
182 CLOSE_READER(re, gb)
183 return code;
184 }