libavcodec/get_bits.h
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00001 /*
00002  * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
00003  *
00004  * This file is part of FFmpeg.
00005  *
00006  * FFmpeg is free software; you can redistribute it and/or
00007  * modify it under the terms of the GNU Lesser General Public
00008  * License as published by the Free Software Foundation; either
00009  * version 2.1 of the License, or (at your option) any later version.
00010  *
00011  * FFmpeg is distributed in the hope that it will be useful,
00012  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00013  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014  * Lesser General Public License for more details.
00015  *
00016  * You should have received a copy of the GNU Lesser General Public
00017  * License along with FFmpeg; if not, write to the Free Software
00018  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00019  */
00020 
00026 #ifndef AVCODEC_GET_BITS_H
00027 #define AVCODEC_GET_BITS_H
00028 
00029 #include <stdint.h>
00030 #include "libavutil/common.h"
00031 #include "libavutil/intreadwrite.h"
00032 #include "libavutil/log.h"
00033 #include "mathops.h"
00034 
00035 /*
00036  * Safe bitstream reading:
00037  * optionally, the get_bits API can check to ensure that we
00038  * don't read past input buffer boundaries. This is protected
00039  * with CONFIG_SAFE_BITSTREAM_READER at the global level, and
00040  * then below that with UNCHECKED_BITSTREAM_READER at the per-
00041  * decoder level. This means that decoders that check internally
00042  * can "#define UNCHECKED_BITSTREAM_READER 1" to disable
00043  * overread checks.
00044  * Boundary checking causes a minor performance penalty so for
00045  * applications that won't want/need this, it can be disabled
00046  * globally using "#define CONFIG_SAFE_BITSTREAM_READER 0".
00047  */
00048 #ifndef UNCHECKED_BITSTREAM_READER
00049 #define UNCHECKED_BITSTREAM_READER !CONFIG_SAFE_BITSTREAM_READER
00050 #endif
00051 
00052 typedef struct GetBitContext {
00053     const uint8_t *buffer, *buffer_end;
00054     int index;
00055     int size_in_bits;
00056     int size_in_bits_plus8;
00057 } GetBitContext;
00058 
00059 #define VLC_TYPE int16_t
00060 
00061 typedef struct VLC {
00062     int bits;
00063     VLC_TYPE (*table)[2]; 
00064     int table_size, table_allocated;
00065 } VLC;
00066 
00067 typedef struct RL_VLC_ELEM {
00068     int16_t level;
00069     int8_t len;
00070     uint8_t run;
00071 } RL_VLC_ELEM;
00072 
00073 /* Bitstream reader API docs:
00074 name
00075     arbitrary name which is used as prefix for the internal variables
00076 
00077 gb
00078     getbitcontext
00079 
00080 OPEN_READER(name, gb)
00081     load gb into local variables
00082 
00083 CLOSE_READER(name, gb)
00084     store local vars in gb
00085 
00086 UPDATE_CACHE(name, gb)
00087     refill the internal cache from the bitstream
00088     after this call at least MIN_CACHE_BITS will be available,
00089 
00090 GET_CACHE(name, gb)
00091     will output the contents of the internal cache, next bit is MSB of 32 or 64 bit (FIXME 64bit)
00092 
00093 SHOW_UBITS(name, gb, num)
00094     will return the next num bits
00095 
00096 SHOW_SBITS(name, gb, num)
00097     will return the next num bits and do sign extension
00098 
00099 SKIP_BITS(name, gb, num)
00100     will skip over the next num bits
00101     note, this is equivalent to SKIP_CACHE; SKIP_COUNTER
00102 
00103 SKIP_CACHE(name, gb, num)
00104     will remove the next num bits from the cache (note SKIP_COUNTER MUST be called before UPDATE_CACHE / CLOSE_READER)
00105 
00106 SKIP_COUNTER(name, gb, num)
00107     will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS)
00108 
00109 LAST_SKIP_BITS(name, gb, num)
00110     like SKIP_BITS, to be used if next call is UPDATE_CACHE or CLOSE_READER
00111 
00112 for examples see get_bits, show_bits, skip_bits, get_vlc
00113 */
00114 
00115 #ifdef LONG_BITSTREAM_READER
00116 #   define MIN_CACHE_BITS 32
00117 #else
00118 #   define MIN_CACHE_BITS 25
00119 #endif
00120 
00121 #if UNCHECKED_BITSTREAM_READER
00122 #define OPEN_READER(name, gb)                   \
00123     unsigned int name##_index = (gb)->index;    \
00124     av_unused unsigned int name##_cache
00125 
00126 #define HAVE_BITS_REMAINING(name, gb) 1
00127 #else
00128 #define OPEN_READER(name, gb)                   \
00129     unsigned int name##_index = (gb)->index;    \
00130     unsigned int av_unused name##_cache = 0;    \
00131     unsigned int av_unused name##_size_plus8 =  \
00132                 (gb)->size_in_bits_plus8
00133 
00134 #define HAVE_BITS_REMAINING(name, gb)           \
00135     name##_index < name##_size_plus8
00136 #endif
00137 
00138 #define CLOSE_READER(name, gb) (gb)->index = name##_index
00139 
00140 #ifdef BITSTREAM_READER_LE
00141 
00142 # ifdef LONG_BITSTREAM_READER
00143 #   define UPDATE_CACHE(name, gb) name##_cache = \
00144         AV_RL64((gb)->buffer + (name##_index >> 3)) >> (name##_index & 7)
00145 # else
00146 #   define UPDATE_CACHE(name, gb) name##_cache = \
00147         AV_RL32((gb)->buffer + (name##_index >> 3)) >> (name##_index & 7)
00148 # endif
00149 
00150 # define SKIP_CACHE(name, gb, num) name##_cache >>= (num)
00151 
00152 #else
00153 
00154 # ifdef LONG_BITSTREAM_READER
00155 #   define UPDATE_CACHE(name, gb) name##_cache = \
00156         AV_RB64((gb)->buffer + (name##_index >> 3)) >> (32 - (name##_index & 7))
00157 # else
00158 #   define UPDATE_CACHE(name, gb) name##_cache = \
00159         AV_RB32((gb)->buffer + (name##_index >> 3)) << (name##_index & 7)
00160 # endif
00161 
00162 # define SKIP_CACHE(name, gb, num) name##_cache <<= (num)
00163 
00164 #endif
00165 
00166 #if UNCHECKED_BITSTREAM_READER
00167 #   define SKIP_COUNTER(name, gb, num) name##_index += (num)
00168 #else
00169 #   define SKIP_COUNTER(name, gb, num) \
00170     name##_index = FFMIN(name##_size_plus8, name##_index + (num))
00171 #endif
00172 
00173 #define SKIP_BITS(name, gb, num) do {           \
00174         SKIP_CACHE(name, gb, num);              \
00175         SKIP_COUNTER(name, gb, num);            \
00176     } while (0)
00177 
00178 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
00179 
00180 #ifdef BITSTREAM_READER_LE
00181 #   define SHOW_UBITS(name, gb, num) zero_extend(name##_cache, num)
00182 #   define SHOW_SBITS(name, gb, num) sign_extend(name##_cache, num)
00183 #else
00184 #   define SHOW_UBITS(name, gb, num) NEG_USR32(name##_cache, num)
00185 #   define SHOW_SBITS(name, gb, num) NEG_SSR32(name##_cache, num)
00186 #endif
00187 
00188 #define GET_CACHE(name, gb) ((uint32_t)name##_cache)
00189 
00190 static inline int get_bits_count(const GetBitContext *s)
00191 {
00192     return s->index;
00193 }
00194 
00195 static inline void skip_bits_long(GetBitContext *s, int n){
00196 #if UNCHECKED_BITSTREAM_READER
00197     s->index += n;
00198 #else
00199     s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
00200 #endif
00201 }
00202 
00208 static inline int get_xbits(GetBitContext *s, int n)
00209 {
00210     register int sign;
00211     register int32_t cache;
00212     OPEN_READER(re, s);
00213     UPDATE_CACHE(re, s);
00214     cache = GET_CACHE(re, s);
00215     sign = ~cache >> 31;
00216     LAST_SKIP_BITS(re, s, n);
00217     CLOSE_READER(re, s);
00218     return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
00219 }
00220 
00221 static inline int get_sbits(GetBitContext *s, int n)
00222 {
00223     register int tmp;
00224     OPEN_READER(re, s);
00225     UPDATE_CACHE(re, s);
00226     tmp = SHOW_SBITS(re, s, n);
00227     LAST_SKIP_BITS(re, s, n);
00228     CLOSE_READER(re, s);
00229     return tmp;
00230 }
00231 
00235 static inline unsigned int get_bits(GetBitContext *s, int n)
00236 {
00237     register int tmp;
00238     OPEN_READER(re, s);
00239     UPDATE_CACHE(re, s);
00240     tmp = SHOW_UBITS(re, s, n);
00241     LAST_SKIP_BITS(re, s, n);
00242     CLOSE_READER(re, s);
00243     return tmp;
00244 }
00245 
00249 static inline unsigned int show_bits(GetBitContext *s, int n)
00250 {
00251     register int tmp;
00252     OPEN_READER(re, s);
00253     UPDATE_CACHE(re, s);
00254     tmp = SHOW_UBITS(re, s, n);
00255     return tmp;
00256 }
00257 
00258 static inline void skip_bits(GetBitContext *s, int n)
00259 {
00260     OPEN_READER(re, s);
00261     UPDATE_CACHE(re, s);
00262     LAST_SKIP_BITS(re, s, n);
00263     CLOSE_READER(re, s);
00264 }
00265 
00266 static inline unsigned int get_bits1(GetBitContext *s)
00267 {
00268     unsigned int index = s->index;
00269     uint8_t result = s->buffer[index>>3];
00270 #ifdef BITSTREAM_READER_LE
00271     result >>= index & 7;
00272     result &= 1;
00273 #else
00274     result <<= index & 7;
00275     result >>= 8 - 1;
00276 #endif
00277 #if !UNCHECKED_BITSTREAM_READER
00278     if (s->index < s->size_in_bits_plus8)
00279 #endif
00280         index++;
00281     s->index = index;
00282 
00283     return result;
00284 }
00285 
00286 static inline unsigned int show_bits1(GetBitContext *s)
00287 {
00288     return show_bits(s, 1);
00289 }
00290 
00291 static inline void skip_bits1(GetBitContext *s)
00292 {
00293     skip_bits(s, 1);
00294 }
00295 
00299 static inline unsigned int get_bits_long(GetBitContext *s, int n)
00300 {
00301     if (n <= MIN_CACHE_BITS)
00302         return get_bits(s, n);
00303     else {
00304 #ifdef BITSTREAM_READER_LE
00305         int ret = get_bits(s, 16);
00306         return ret | (get_bits(s, n-16) << 16);
00307 #else
00308         int ret = get_bits(s, 16) << (n-16);
00309         return ret | get_bits(s, n-16);
00310 #endif
00311     }
00312 }
00313 
00317 static inline int get_sbits_long(GetBitContext *s, int n)
00318 {
00319     return sign_extend(get_bits_long(s, n), n);
00320 }
00321 
00325 static inline unsigned int show_bits_long(GetBitContext *s, int n)
00326 {
00327     if (n <= MIN_CACHE_BITS)
00328         return show_bits(s, n);
00329     else {
00330         GetBitContext gb = *s;
00331         return get_bits_long(&gb, n);
00332     }
00333 }
00334 
00335 static inline int check_marker(GetBitContext *s, const char *msg)
00336 {
00337     int bit = get_bits1(s);
00338     if (!bit)
00339         av_log(NULL, AV_LOG_INFO, "Marker bit missing %s\n", msg);
00340 
00341     return bit;
00342 }
00343 
00350 static inline void init_get_bits(GetBitContext *s, const uint8_t *buffer,
00351                                  int bit_size)
00352 {
00353     int buffer_size = (bit_size+7)>>3;
00354     if (buffer_size < 0 || bit_size < 0) {
00355         buffer_size = bit_size = 0;
00356         buffer = NULL;
00357     }
00358 
00359     s->buffer       = buffer;
00360     s->size_in_bits = bit_size;
00361     s->size_in_bits_plus8 = bit_size + 8;
00362     s->buffer_end   = buffer + buffer_size;
00363     s->index        = 0;
00364 }
00365 
00366 static inline void align_get_bits(GetBitContext *s)
00367 {
00368     int n = -get_bits_count(s) & 7;
00369     if (n) skip_bits(s, n);
00370 }
00371 
00372 #define init_vlc(vlc, nb_bits, nb_codes,                \
00373                  bits, bits_wrap, bits_size,            \
00374                  codes, codes_wrap, codes_size,         \
00375                  flags)                                 \
00376         ff_init_vlc_sparse(vlc, nb_bits, nb_codes,         \
00377                            bits, bits_wrap, bits_size,     \
00378                            codes, codes_wrap, codes_size,  \
00379                            NULL, 0, 0, flags)
00380 
00381 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
00382              const void *bits, int bits_wrap, int bits_size,
00383              const void *codes, int codes_wrap, int codes_size,
00384              const void *symbols, int symbols_wrap, int symbols_size,
00385              int flags);
00386 #define INIT_VLC_LE         2
00387 #define INIT_VLC_USE_NEW_STATIC 4
00388 void ff_free_vlc(VLC *vlc);
00389 
00390 #define INIT_VLC_STATIC(vlc, bits, a,b,c,d,e,f,g, static_size) do {     \
00391         static VLC_TYPE table[static_size][2];                          \
00392         (vlc)->table = table;                                           \
00393         (vlc)->table_allocated = static_size;                           \
00394         init_vlc(vlc, bits, a,b,c,d,e,f,g, INIT_VLC_USE_NEW_STATIC);    \
00395     } while (0)
00396 
00397 
00403 #define GET_VLC(code, name, gb, table, bits, max_depth)         \
00404     do {                                                        \
00405         int n, nb_bits;                                         \
00406         unsigned int index;                                     \
00407                                                                 \
00408         index = SHOW_UBITS(name, gb, bits);                     \
00409         code  = table[index][0];                                \
00410         n     = table[index][1];                                \
00411                                                                 \
00412         if (max_depth > 1 && n < 0) {                           \
00413             LAST_SKIP_BITS(name, gb, bits);                     \
00414             UPDATE_CACHE(name, gb);                             \
00415                                                                 \
00416             nb_bits = -n;                                       \
00417                                                                 \
00418             index = SHOW_UBITS(name, gb, nb_bits) + code;       \
00419             code  = table[index][0];                            \
00420             n     = table[index][1];                            \
00421             if (max_depth > 2 && n < 0) {                       \
00422                 LAST_SKIP_BITS(name, gb, nb_bits);              \
00423                 UPDATE_CACHE(name, gb);                         \
00424                                                                 \
00425                 nb_bits = -n;                                   \
00426                                                                 \
00427                 index = SHOW_UBITS(name, gb, nb_bits) + code;   \
00428                 code  = table[index][0];                        \
00429                 n     = table[index][1];                        \
00430             }                                                   \
00431         }                                                       \
00432         SKIP_BITS(name, gb, n);                                 \
00433     } while (0)
00434 
00435 #define GET_RL_VLC(level, run, name, gb, table, bits, max_depth, need_update) \
00436     do {                                                                \
00437         int n, nb_bits;                                                 \
00438         unsigned int index;                                             \
00439                                                                         \
00440         index = SHOW_UBITS(name, gb, bits);                             \
00441         level = table[index].level;                                     \
00442         n     = table[index].len;                                       \
00443                                                                         \
00444         if (max_depth > 1 && n < 0) {                                   \
00445             SKIP_BITS(name, gb, bits);                                  \
00446             if (need_update) {                                          \
00447                 UPDATE_CACHE(name, gb);                                 \
00448             }                                                           \
00449                                                                         \
00450             nb_bits = -n;                                               \
00451                                                                         \
00452             index = SHOW_UBITS(name, gb, nb_bits) + level;              \
00453             level = table[index].level;                                 \
00454             n     = table[index].len;                                   \
00455         }                                                               \
00456         run = table[index].run;                                         \
00457         SKIP_BITS(name, gb, n);                                         \
00458     } while (0)
00459 
00460 
00469 static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE (*table)[2],
00470                                      int bits, int max_depth)
00471 {
00472     int code;
00473 
00474     OPEN_READER(re, s);
00475     UPDATE_CACHE(re, s);
00476 
00477     GET_VLC(code, re, s, table, bits, max_depth);
00478 
00479     CLOSE_READER(re, s);
00480     return code;
00481 }
00482 
00483 static inline int decode012(GetBitContext *gb)
00484 {
00485     int n;
00486     n = get_bits1(gb);
00487     if (n == 0)
00488         return 0;
00489     else
00490         return get_bits1(gb) + 1;
00491 }
00492 
00493 static inline int decode210(GetBitContext *gb)
00494 {
00495     if (get_bits1(gb))
00496         return 0;
00497     else
00498         return 2 - get_bits1(gb);
00499 }
00500 
00501 static inline int get_bits_left(GetBitContext *gb)
00502 {
00503     return gb->size_in_bits - get_bits_count(gb);
00504 }
00505 
00506 //#define TRACE
00507 
00508 #ifdef TRACE
00509 static inline void print_bin(int bits, int n)
00510 {
00511     int i;
00512 
00513     for (i = n-1; i >= 0; i--) {
00514         av_log(NULL, AV_LOG_DEBUG, "%d", (bits>>i)&1);
00515     }
00516     for (i = n; i < 24; i++)
00517         av_log(NULL, AV_LOG_DEBUG, " ");
00518 }
00519 
00520 static inline int get_bits_trace(GetBitContext *s, int n, char *file,
00521                                  const char *func, int line)
00522 {
00523     int r = get_bits(s, n);
00524 
00525     print_bin(r, n);
00526     av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d bit @%5d in %s %s:%d\n",
00527            r, n, r, get_bits_count(s)-n, file, func, line);
00528     return r;
00529 }
00530 static inline int get_vlc_trace(GetBitContext *s, VLC_TYPE (*table)[2],
00531                                 int bits, int max_depth, char *file,
00532                                 const char *func, int line)
00533 {
00534     int show  = show_bits(s, 24);
00535     int pos   = get_bits_count(s);
00536     int r     = get_vlc2(s, table, bits, max_depth);
00537     int len   = get_bits_count(s) - pos;
00538     int bits2 = show >> (24-len);
00539 
00540     print_bin(bits2, len);
00541 
00542     av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d vlc @%5d in %s %s:%d\n",
00543            bits2, len, r, pos, file, func, line);
00544     return r;
00545 }
00546 static inline int get_xbits_trace(GetBitContext *s, int n, char *file,
00547                                   const char *func, int line)
00548 {
00549     int show = show_bits(s, n);
00550     int r    = get_xbits(s, n);
00551 
00552     print_bin(show, n);
00553     av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d xbt @%5d in %s %s:%d\n",
00554            show, n, r, get_bits_count(s)-n, file, func, line);
00555     return r;
00556 }
00557 
00558 #define get_bits(s, n)  get_bits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00559 #define get_bits1(s)    get_bits_trace(s, 1, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00560 #define get_xbits(s, n) get_xbits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00561 #define get_vlc(s, vlc)            get_vlc_trace(s, (vlc)->table, (vlc)->bits, 3, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00562 #define get_vlc2(s, tab, bits, max) get_vlc_trace(s, tab, bits, max, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00563 
00564 #define tprintf(p, ...) av_log(p, AV_LOG_DEBUG, __VA_ARGS__)
00565 
00566 #else //TRACE
00567 #define tprintf(p, ...) {}
00568 #endif
00569 
00570 #endif /* AVCODEC_GET_BITS_H */