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comparison libavcodec/get_bits.h @ 9:ea1ba68cf0ed

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update to match api changes + add sscc produced source
author Nina Engelhardt <nengel@mailbox.tu-berlin.de>
date Wed, 05 Jun 2013 14:43:26 +0200
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1 /*
2 * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
3 *
4 * This file is part of FFmpeg.
5 *
6 * FFmpeg is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
10 *
11 * FFmpeg is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with FFmpeg; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19 */
20
21 /**
22 * @file
23 * bitstream reader API header.
24 */
25
26 #ifndef AVCODEC_GET_BITS_H
27 #define AVCODEC_GET_BITS_H
28
29 #include <stdint.h>
30 #include <stdlib.h>
31 #include <assert.h>
32 #include "libavutil/bswap.h"
33 #include "libavutil/common.h"
34 #include "libavutil/intreadwrite.h"
35 #include "libavutil/log.h"
36 #include "mathops.h"
37
38
39 typedef struct GetBitContext {
40 uint8_t *rbsp;
41 unsigned int rbsp_size;
42 uint8_t *raw;
43 const uint8_t *buffer, *buffer_end;
44 unsigned int alloc_size;
45 unsigned int buf_size;
46 uint32_t *buffer_ptr;
47 uint32_t cache0;
48 uint32_t cache1;
49 int bit_count;
50 int size_in_bits;
51 } GetBitContext;
52
53 /* Bitstream reader API docs:
54 name
55 arbitrary name which is used as prefix for the internal variables
56
57 gb
58 getbitcontext
59
60 OPEN_READER(name, gb)
61 loads gb into local variables
62
63 CLOSE_READER(name, gb)
64 stores local vars in gb
65
66 UPDATE_CACHE(name, gb)
67 refills the internal cache from the bitstream
68 after this call at least MIN_CACHE_BITS will be available,
69
70 GET_CACHE(name, gb)
71 will output the contents of the internal cache, next bit is MSB of 32 or 64 bit (FIXME 64bit)
72
73 SHOW_UBITS(name, gb, num)
74 will return the next num bits
75
76 SHOW_SBITS(name, gb, num)
77 will return the next num bits and do sign extension
78
79 SKIP_BITS(name, gb, num)
80 will skip over the next num bits
81 note, this is equivalent to SKIP_CACHE; SKIP_COUNTER
82
83 SKIP_CACHE(name, gb, num)
84 will remove the next num bits from the cache (note SKIP_COUNTER MUST be called before UPDATE_CACHE / CLOSE_READER)
85
86 SKIP_COUNTER(name, gb, num)
87 will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS)
88
89 LAST_SKIP_CACHE(name, gb, num)
90 will remove the next num bits from the cache if it is needed for UPDATE_CACHE otherwise it will do nothing
91
92 LAST_SKIP_BITS(name, gb, num)
93 is equivalent to LAST_SKIP_CACHE; SKIP_COUNTER
94
95 for examples see get_bits, show_bits, skip_bits, get_vlc
96 */
97
98 #define MIN_CACHE_BITS 32
99
100 #define OPEN_READER(name, gb)\
101 int name##_bit_count=(gb)->bit_count;\
102 uint32_t name##_cache0= (gb)->cache0;\
103 uint32_t name##_cache1= (gb)->cache1;\
104 uint32_t * name##_buffer_ptr=(gb)->buffer_ptr;\
105
106 #define CLOSE_READER(name, gb)\
107 (gb)->bit_count= name##_bit_count;\
108 (gb)->cache0= name##_cache0;\
109 (gb)->cache1= name##_cache1;\
110 (gb)->buffer_ptr= name##_buffer_ptr;\
111
112 #define UPDATE_CACHE(name, gb)\
113 if(name##_bit_count > 0){\
114 const uint32_t next= be2me_32( *name##_buffer_ptr );\
115 name##_cache0 |= NEG_USR32(next,name##_bit_count);\
116 name##_cache1 |= next<<name##_bit_count;\
117 name##_buffer_ptr++;\
118 name##_bit_count-= 32;\
119 }\
120
121 #if ARCH_X86
122 # define SKIP_CACHE(name, gb, num)\
123 __asm__(\
124 "shldl %2, %1, %0 \n\t"\
125 "shll %2, %1 \n\t"\
126 : "+r" (name##_cache0), "+r" (name##_cache1)\
127 : "Ic" ((uint8_t)(num))\
128 );
129 #else
130 # define SKIP_CACHE(name, gb, num)\
131 name##_cache0 <<= (num);\
132 name##_cache0 |= NEG_USR32(name##_cache1,num);\
133 name##_cache1 <<= (num);
134 #endif
135
136 #define SKIP_COUNTER(name, gb, num)\
137 name##_bit_count += (num);\
138
139 #define SKIP_BITS(name, gb, num)\
140 {\
141 SKIP_CACHE(name, gb, num)\
142 SKIP_COUNTER(name, gb, num)\
143 }\
144
145 #define LAST_SKIP_BITS(name, gb, num) SKIP_BITS(name, gb, num)
146 #define LAST_SKIP_CACHE(name, gb, num) SKIP_CACHE(name, gb, num)
147
148 #define SHOW_UBITS(name, gb, num)\
149 NEG_USR32(name##_cache0, num)
150
151 #define SHOW_SBITS(name, gb, num)\
152 NEG_SSR32(name##_cache0, num)
153
154 #define GET_CACHE(name, gb)\
155 (name##_cache0)
156
157 static inline int get_bits_count(const GetBitContext *s){
158 return ((uint8_t*)s->buffer_ptr - s->buffer)*8 - 32 + s->bit_count;
159 }
160
161 static inline void skip_bits_long(GetBitContext *s, int n){
162 OPEN_READER(re, s)
163 re_bit_count += n;
164 re_buffer_ptr += re_bit_count>>5;
165 re_bit_count &= 31;
166 re_cache0 = be2me_32( re_buffer_ptr[-1] ) << re_bit_count;
167 re_cache1 = 0;
168 UPDATE_CACHE(re, s)
169 CLOSE_READER(re, s)
170 }
171
172 /**
173 * read mpeg1 dc style vlc (sign bit + mantisse with no MSB).
174 * if MSB not set it is negative
175 * @param n length in bits
176 * @author BERO
177 */
178 static inline int get_xbits(GetBitContext *s, int n){
179 register int sign;
180 register int32_t cache;
181 OPEN_READER(re, s)
182 UPDATE_CACHE(re, s)
183 cache = GET_CACHE(re,s);
184 sign=(~cache)>>31;
185 LAST_SKIP_BITS(re, s, n)
186 CLOSE_READER(re, s)
187 return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
188 }
189
190 static inline int get_sbits(GetBitContext *s, int n){
191 register int tmp;
192 OPEN_READER(re, s)
193 UPDATE_CACHE(re, s)
194 tmp= SHOW_SBITS(re, s, n);
195 LAST_SKIP_BITS(re, s, n)
196 CLOSE_READER(re, s)
197 return tmp;
198 }
199
200 /**
201 * reads 1-17 bits.
202 * Note, the alt bitstream reader can read up to 25 bits, but the libmpeg2 reader can't
203 */
204 static inline unsigned int get_bits(GetBitContext *s, int n){
205 register int tmp;
206 OPEN_READER(re, s)
207 UPDATE_CACHE(re, s)
208 tmp= SHOW_UBITS(re, s, n);
209 LAST_SKIP_BITS(re, s, n)
210 CLOSE_READER(re, s)
211 return tmp;
212 }
213
214 /**
215 * shows 1-17 bits.
216 * Note, the alt bitstream reader can read up to 25 bits, but the libmpeg2 reader can't
217 */
218 static inline unsigned int show_bits(GetBitContext *s, int n){
219 register int tmp;
220 OPEN_READER(re, s)
221 UPDATE_CACHE(re, s)
222 tmp= SHOW_UBITS(re, s, n);
223 // CLOSE_READER(re, s)
224 return tmp;
225 }
226
227 static inline void skip_bits(GetBitContext *s, int n){
228 //Note gcc seems to optimize this to s->index+=n for the ALT_READER :))
229 OPEN_READER(re, s)
230 UPDATE_CACHE(re, s)
231 LAST_SKIP_BITS(re, s, n)
232 CLOSE_READER(re, s)
233 }
234
235 static inline unsigned int get_bits1(GetBitContext *s){
236 return get_bits(s, 1);
237 }
238
239 static inline unsigned int show_bits1(GetBitContext *s){
240 return show_bits(s, 1);
241 }
242
243 static inline void skip_bits1(GetBitContext *s){
244 skip_bits(s, 1);
245 }
246
247 /**
248 * reads 0-32 bits.
249 */
250 static inline unsigned int get_bits_long(GetBitContext *s, int n){
251 if(n<=MIN_CACHE_BITS) return get_bits(s, n);
252 else{
253 int ret= get_bits(s, 16) << (n-16);
254 return ret | get_bits(s, n-16);
255 }
256 }
257
258 /**
259 * reads 0-32 bits as a signed integer.
260 */
261 static inline int get_sbits_long(GetBitContext *s, int n) {
262 return sign_extend(get_bits_long(s, n), n);
263 }
264
265 /**
266 * shows 0-32 bits.
267 */
268 static inline unsigned int show_bits_long(GetBitContext *s, int n){
269 if(n<=MIN_CACHE_BITS) return show_bits(s, n);
270 else{
271 GetBitContext gb= *s;
272 return get_bits_long(&gb, n);
273 }
274 }
275
276 static inline int check_marker(GetBitContext *s, const char *msg)
277 {
278 int bit= get_bits1(s);
279 if(!bit)
280 av_log(AV_LOG_INFO, "Marker bit missing %s\n", msg);
281
282 return bit;
283 }
284
285 /**
286 * init GetBitContext.
287 * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes larger then the actual read bits
288 * because some optimized bitstream readers read 32 or 64 bit at once and could read over the end
289 * @param bit_size the size of the buffer in bits
290 *
291 * While GetBitContext stores the buffer size, for performance reasons you are
292 * responsible for checking for the buffer end yourself (take advantage of the padding)!
293 */
294 static inline void init_get_bits(GetBitContext *s,
295 const uint8_t *buffer, int bit_size)
296 {
297 int buffer_size= (bit_size+7)>>3;
298 if(buffer_size < 0 || bit_size < 0) {
299 buffer_size = bit_size = 0;
300 buffer = NULL;
301 }
302
303 s->buffer= buffer;
304 s->size_in_bits= bit_size;
305 s->buffer_end= buffer + buffer_size;
306
307 s->buffer_ptr = (uint32_t*)((intptr_t)buffer&(~3));
308 s->bit_count = 32 + 8*((intptr_t)buffer&3);
309 skip_bits_long(s, 0);
310 }
311
312 static inline void align_get_bits(GetBitContext *s)
313 {
314 int n= (-get_bits_count(s)) & 7;
315 if(n) skip_bits(s, n);
316 }
317
318 #define tprintf(p, ...) {}
319
320 static inline int get_bits_left(GetBitContext *gb)
321 {
322 return gb->size_in_bits - get_bits_count(gb);
323 }
324
325 #endif /* AVCODEC_GET_BITS_H */