Kill unused getbit_context->size_in_bits and add some doku.
[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( ((const uint8_t *)(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 /** This is equivalent to SKIP_LAST_CACHE; SKIP_COUNTER. */
81 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
82
83 /** Return the next num bits. */
84 #define SHOW_UBITS(name, gb, num)\
85 NEG_USR32(name##_cache, num)
86
87 static inline int get_bits_count(struct getbit_context *s)
88 {
89 return s->index;
90 }
91
92 /**
93 * Read 1-17 bits.
94 */
95 static inline unsigned int get_bits(struct getbit_context *s, int n)
96 {
97 register int tmp;
98 OPEN_READER(re, s)
99 UPDATE_CACHE(re, s)
100 tmp = SHOW_UBITS(re, s, n);
101 LAST_SKIP_BITS(re, s, n)
102 CLOSE_READER(re, s)
103 return tmp;
104 }
105
106 /**
107 * Show 1-17 bits.
108 */
109 static inline unsigned int show_bits(struct getbit_context *s, int n)
110 {
111 register int tmp;
112 OPEN_READER(re, s)
113 UPDATE_CACHE(re, s)
114 tmp = SHOW_UBITS(re, s, n);
115 return tmp;
116 }
117
118 static inline void skip_bits(struct getbit_context *s, int n)
119 {
120 /* gcc seems to optimize this to s->index+=n for the ALT_READER :)) */
121 OPEN_READER(re, s)
122 UPDATE_CACHE(re, s)
123 LAST_SKIP_BITS(re, s, n)
124 CLOSE_READER(re, s)
125 }
126
127 static inline unsigned int get_bits1(struct getbit_context *s)
128 {
129 int idx = s->index;
130 uint8_t result = s->buffer[idx >> 3];
131
132 result <<= (idx & 0x07);
133 result >>= 8 - 1;
134 idx++;
135 s->index = idx;
136 return result;
137 }
138
139 /**
140 * Initialize a getbit_context structure.
141 *
142 * \param buffer The bitstream buffer. It must be FF_INPUT_BUFFER_PADDING_SIZE
143 * bytes larger then the actual read bits * because some optimized bitstream
144 * readers read 32 or 64 bit at once and could read over the end.
145 *
146 * \param bit_size The size of the buffer in bits.
147 */
148 static inline void init_get_bits(struct getbit_context *s,
149 const uint8_t *buffer, int bit_size)
150 {
151 int buffer_size = (bit_size + 7) >> 3;
152 if (buffer_size < 0 || bit_size < 0) {
153 buffer_size = bit_size = 0;
154 buffer = NULL;
155 }
156 s->buffer = buffer;
157 s->buffer_end = buffer + buffer_size;
158 s->index = 0;
159 }
160
161 void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
162 const void *codes, int codes_size);
163
164 void free_vlc(struct vlc *vlc);
165
166 /**
167 *
168 * if the vlc code is invalid and max_depth=1 than no bits will be removed
169 * if the vlc code is invalid and max_depth>1 than the number of bits removed
170 * is undefined
171 */
172 #define GET_VLC(code, name, gb, table, bits, max_depth)\
173 {\
174 int n, index, nb_bits;\
175 \
176 index= SHOW_UBITS(name, gb, bits);\
177 code = table[index][0];\
178 n = table[index][1];\
179 \
180 if(max_depth > 1 && n < 0){\
181 LAST_SKIP_BITS(name, gb, bits)\
182 UPDATE_CACHE(name, gb)\
183 \
184 nb_bits = -n;\
185 \
186 index= SHOW_UBITS(name, gb, nb_bits) + code;\
187 code = table[index][0];\
188 n = table[index][1];\
189 if(max_depth > 2 && n < 0){\
190 LAST_SKIP_BITS(name, gb, nb_bits)\
191 UPDATE_CACHE(name, gb)\
192 \
193 nb_bits = -n;\
194 \
195 index= SHOW_UBITS(name, gb, nb_bits) + code;\
196 code = table[index][0];\
197 n = table[index][1];\
198 }\
199 }\
200 SKIP_BITS(name, gb, n)\
201 }