• Main Page
  • Related Pages
  • Modules
  • Data Structures
  • Files
  • Examples
  • File List
  • Globals

libavcodec/get_bits.h

Go to the documentation of this file.
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 <stdlib.h>
00031 #include <assert.h>
00032 #include "libavutil/bswap.h"
00033 #include "libavutil/common.h"
00034 #include "libavutil/intreadwrite.h"
00035 #include "libavutil/log.h"
00036 #include "mathops.h"
00037 
00038 #if defined(ALT_BITSTREAM_READER_LE) && !defined(ALT_BITSTREAM_READER)
00039 #   define ALT_BITSTREAM_READER
00040 #endif
00041 
00042 #if !defined(A32_BITSTREAM_READER) && !defined(ALT_BITSTREAM_READER)
00043 #   if ARCH_ARM && !HAVE_FAST_UNALIGNED
00044 #       define A32_BITSTREAM_READER
00045 #   else
00046 #       define ALT_BITSTREAM_READER
00047 //#define A32_BITSTREAM_READER
00048 #   endif
00049 #endif
00050 
00051 /* bit input */
00052 /* buffer, buffer_end and size_in_bits must be present and used by every reader */
00053 typedef struct GetBitContext {
00054     const uint8_t *buffer, *buffer_end;
00055 #ifdef ALT_BITSTREAM_READER
00056     int index;
00057 #elif defined A32_BITSTREAM_READER
00058     uint32_t *buffer_ptr;
00059     uint32_t cache0;
00060     uint32_t cache1;
00061     int bit_count;
00062 #endif
00063     int size_in_bits;
00064 } GetBitContext;
00065 
00066 #define VLC_TYPE int16_t
00067 
00068 typedef struct VLC {
00069     int bits;
00070     VLC_TYPE (*table)[2]; 
00071     int table_size, table_allocated;
00072 } VLC;
00073 
00074 typedef struct RL_VLC_ELEM {
00075     int16_t level;
00076     int8_t len;
00077     uint8_t run;
00078 } RL_VLC_ELEM;
00079 
00080 /* Bitstream reader API docs:
00081 name
00082     arbitrary name which is used as prefix for the internal variables
00083 
00084 gb
00085     getbitcontext
00086 
00087 OPEN_READER(name, gb)
00088     loads gb into local variables
00089 
00090 CLOSE_READER(name, gb)
00091     stores local vars in gb
00092 
00093 UPDATE_CACHE(name, gb)
00094     refills the internal cache from the bitstream
00095     after this call at least MIN_CACHE_BITS will be available,
00096 
00097 GET_CACHE(name, gb)
00098     will output the contents of the internal cache, next bit is MSB of 32 or 64 bit (FIXME 64bit)
00099 
00100 SHOW_UBITS(name, gb, num)
00101     will return the next num bits
00102 
00103 SHOW_SBITS(name, gb, num)
00104     will return the next num bits and do sign extension
00105 
00106 SKIP_BITS(name, gb, num)
00107     will skip over the next num bits
00108     note, this is equivalent to SKIP_CACHE; SKIP_COUNTER
00109 
00110 SKIP_CACHE(name, gb, num)
00111     will remove the next num bits from the cache (note SKIP_COUNTER MUST be called before UPDATE_CACHE / CLOSE_READER)
00112 
00113 SKIP_COUNTER(name, gb, num)
00114     will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS)
00115 
00116 LAST_SKIP_CACHE(name, gb, num)
00117     will remove the next num bits from the cache if it is needed for UPDATE_CACHE otherwise it will do nothing
00118 
00119 LAST_SKIP_BITS(name, gb, num)
00120     is equivalent to LAST_SKIP_CACHE; SKIP_COUNTER
00121 
00122 for examples see get_bits, show_bits, skip_bits, get_vlc
00123 */
00124 
00125 #ifdef ALT_BITSTREAM_READER
00126 #   define MIN_CACHE_BITS 25
00127 
00128 #   define OPEN_READER(name, gb)                \
00129     unsigned int name##_index = (gb)->index;    \
00130     av_unused unsigned int name##_cache
00131 
00132 #   define CLOSE_READER(name, gb) (gb)->index = name##_index
00133 
00134 # ifdef ALT_BITSTREAM_READER_LE
00135 #   define UPDATE_CACHE(name, gb) \
00136     name##_cache = AV_RL32(((const uint8_t *)(gb)->buffer)+(name##_index>>3)) >> (name##_index&0x07)
00137 
00138 #   define SKIP_CACHE(name, gb, num) name##_cache >>= (num)
00139 # else
00140 #   define UPDATE_CACHE(name, gb) \
00141     name##_cache = AV_RB32(((const uint8_t *)(gb)->buffer)+(name##_index>>3)) << (name##_index&0x07)
00142 
00143 #   define SKIP_CACHE(name, gb, num) name##_cache <<= (num)
00144 # endif
00145 
00146 // FIXME name?
00147 #   define SKIP_COUNTER(name, gb, num) name##_index += (num)
00148 
00149 #   define SKIP_BITS(name, gb, num) do {        \
00150         SKIP_CACHE(name, gb, num);              \
00151         SKIP_COUNTER(name, gb, num);            \
00152     } while (0)
00153 
00154 #   define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
00155 #   define LAST_SKIP_CACHE(name, gb, num)
00156 
00157 # ifdef ALT_BITSTREAM_READER_LE
00158 #   define SHOW_UBITS(name, gb, num) zero_extend(name##_cache, num)
00159 
00160 #   define SHOW_SBITS(name, gb, num) sign_extend(name##_cache, num)
00161 # else
00162 #   define SHOW_UBITS(name, gb, num) NEG_USR32(name##_cache, num)
00163 
00164 #   define SHOW_SBITS(name, gb, num) NEG_SSR32(name##_cache, num)
00165 # endif
00166 
00167 #   define GET_CACHE(name, gb) ((uint32_t)name##_cache)
00168 
00169 static inline int get_bits_count(const GetBitContext *s){
00170     return s->index;
00171 }
00172 
00173 static inline void skip_bits_long(GetBitContext *s, int n){
00174     s->index += n;
00175 }
00176 
00177 #elif defined A32_BITSTREAM_READER
00178 
00179 #   define MIN_CACHE_BITS 32
00180 
00181 #   define OPEN_READER(name, gb)                        \
00182     int name##_bit_count        = (gb)->bit_count;      \
00183     uint32_t name##_cache0      = (gb)->cache0;         \
00184     uint32_t name##_cache1      = (gb)->cache1;         \
00185     uint32_t *name##_buffer_ptr = (gb)->buffer_ptr
00186 
00187 #   define CLOSE_READER(name, gb) do {          \
00188         (gb)->bit_count  = name##_bit_count;    \
00189         (gb)->cache0     = name##_cache0;       \
00190         (gb)->cache1     = name##_cache1;       \
00191         (gb)->buffer_ptr = name##_buffer_ptr;   \
00192     } while (0)
00193 
00194 #   define UPDATE_CACHE(name, gb) do {                                  \
00195         if(name##_bit_count > 0){                                       \
00196             const uint32_t next = av_be2ne32(*name##_buffer_ptr);       \
00197             name##_cache0 |= NEG_USR32(next, name##_bit_count);         \
00198             name##_cache1 |= next << name##_bit_count;                  \
00199             name##_buffer_ptr++;                                        \
00200             name##_bit_count -= 32;                                     \
00201         }                                                               \
00202     } while (0)
00203 
00204 #if ARCH_X86
00205 #   define SKIP_CACHE(name, gb, num)                            \
00206     __asm__("shldl %2, %1, %0          \n\t"                    \
00207             "shll  %2, %1              \n\t"                    \
00208             : "+r" (name##_cache0), "+r" (name##_cache1)        \
00209             : "Ic" ((uint8_t)(num)))
00210 #else
00211 #   define SKIP_CACHE(name, gb, num) do {               \
00212         name##_cache0 <<= (num);                        \
00213         name##_cache0 |= NEG_USR32(name##_cache1,num);  \
00214         name##_cache1 <<= (num);                        \
00215     } while (0)
00216 #endif
00217 
00218 #   define SKIP_COUNTER(name, gb, num) name##_bit_count += (num)
00219 
00220 #   define SKIP_BITS(name, gb, num) do {        \
00221         SKIP_CACHE(name, gb, num);              \
00222         SKIP_COUNTER(name, gb, num);            \
00223     } while (0)
00224 
00225 #   define LAST_SKIP_BITS(name, gb, num)  SKIP_BITS(name, gb, num)
00226 #   define LAST_SKIP_CACHE(name, gb, num) SKIP_CACHE(name, gb, num)
00227 
00228 #   define SHOW_UBITS(name, gb, num) NEG_USR32(name##_cache0, num)
00229 
00230 #   define SHOW_SBITS(name, gb, num) NEG_SSR32(name##_cache0, num)
00231 
00232 #   define GET_CACHE(name, gb) name##_cache0
00233 
00234 static inline int get_bits_count(const GetBitContext *s) {
00235     return ((uint8_t*)s->buffer_ptr - s->buffer)*8 - 32 + s->bit_count;
00236 }
00237 
00238 static inline void skip_bits_long(GetBitContext *s, int n){
00239     OPEN_READER(re, s);
00240     re_bit_count += n;
00241     re_buffer_ptr += re_bit_count>>5;
00242     re_bit_count &= 31;
00243     re_cache0 = av_be2ne32(re_buffer_ptr[-1]) << re_bit_count;
00244     re_cache1 = 0;
00245     UPDATE_CACHE(re, s);
00246     CLOSE_READER(re, s);
00247 }
00248 
00249 #endif
00250 
00257 static inline int get_xbits(GetBitContext *s, int n){
00258     register int sign;
00259     register int32_t cache;
00260     OPEN_READER(re, s);
00261     UPDATE_CACHE(re, s);
00262     cache = GET_CACHE(re, s);
00263     sign = ~cache >> 31;
00264     LAST_SKIP_BITS(re, s, n);
00265     CLOSE_READER(re, s);
00266     return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
00267 }
00268 
00269 static inline int get_sbits(GetBitContext *s, int n){
00270     register int tmp;
00271     OPEN_READER(re, s);
00272     UPDATE_CACHE(re, s);
00273     tmp = SHOW_SBITS(re, s, n);
00274     LAST_SKIP_BITS(re, s, n);
00275     CLOSE_READER(re, s);
00276     return tmp;
00277 }
00278 
00282 static inline unsigned int get_bits(GetBitContext *s, int n){
00283     register int tmp;
00284     OPEN_READER(re, s);
00285     UPDATE_CACHE(re, s);
00286     tmp = SHOW_UBITS(re, s, n);
00287     LAST_SKIP_BITS(re, s, n);
00288     CLOSE_READER(re, s);
00289     return tmp;
00290 }
00291 
00295 static inline unsigned int show_bits(GetBitContext *s, int n){
00296     register int tmp;
00297     OPEN_READER(re, s);
00298     UPDATE_CACHE(re, s);
00299     tmp = SHOW_UBITS(re, s, n);
00300     return tmp;
00301 }
00302 
00303 static inline void skip_bits(GetBitContext *s, int n){
00304  //Note gcc seems to optimize this to s->index+=n for the ALT_READER :))
00305     OPEN_READER(re, s);
00306     UPDATE_CACHE(re, s);
00307     LAST_SKIP_BITS(re, s, n);
00308     CLOSE_READER(re, s);
00309 }
00310 
00311 static inline unsigned int get_bits1(GetBitContext *s){
00312 #ifdef ALT_BITSTREAM_READER
00313     unsigned int index = s->index;
00314     uint8_t result = s->buffer[index>>3];
00315 #ifdef ALT_BITSTREAM_READER_LE
00316     result >>= index & 7;
00317     result &= 1;
00318 #else
00319     result <<= index & 7;
00320     result >>= 8 - 1;
00321 #endif
00322     index++;
00323     s->index = index;
00324 
00325     return result;
00326 #else
00327     return get_bits(s, 1);
00328 #endif
00329 }
00330 
00331 static inline unsigned int show_bits1(GetBitContext *s){
00332     return show_bits(s, 1);
00333 }
00334 
00335 static inline void skip_bits1(GetBitContext *s){
00336     skip_bits(s, 1);
00337 }
00338 
00342 static inline unsigned int get_bits_long(GetBitContext *s, int n){
00343     if (n <= MIN_CACHE_BITS) return get_bits(s, n);
00344     else {
00345 #ifdef ALT_BITSTREAM_READER_LE
00346         int ret = get_bits(s, 16);
00347         return ret | (get_bits(s, n-16) << 16);
00348 #else
00349         int ret = get_bits(s, 16) << (n-16);
00350         return ret | get_bits(s, n-16);
00351 #endif
00352     }
00353 }
00354 
00358 static inline int get_sbits_long(GetBitContext *s, int n) {
00359     return sign_extend(get_bits_long(s, n), n);
00360 }
00361 
00365 static inline unsigned int show_bits_long(GetBitContext *s, int n){
00366     if (n <= MIN_CACHE_BITS) return show_bits(s, n);
00367     else {
00368         GetBitContext gb = *s;
00369         return get_bits_long(&gb, n);
00370     }
00371 }
00372 
00373 static inline int check_marker(GetBitContext *s, const char *msg)
00374 {
00375     int bit = get_bits1(s);
00376     if (!bit)
00377         av_log(NULL, AV_LOG_INFO, "Marker bit missing %s\n", msg);
00378 
00379     return bit;
00380 }
00381 
00391 static inline void init_get_bits(GetBitContext *s,
00392                    const uint8_t *buffer, int bit_size)
00393 {
00394     int buffer_size = (bit_size+7)>>3;
00395     if (buffer_size < 0 || bit_size < 0) {
00396         buffer_size = bit_size = 0;
00397         buffer = NULL;
00398     }
00399 
00400     s->buffer       = buffer;
00401     s->size_in_bits = bit_size;
00402     s->buffer_end   = buffer + buffer_size;
00403 #ifdef ALT_BITSTREAM_READER
00404     s->index        = 0;
00405 #elif defined A32_BITSTREAM_READER
00406     s->buffer_ptr   = (uint32_t*)((intptr_t)buffer & ~3);
00407     s->bit_count    = 32 +     8*((intptr_t)buffer &  3);
00408     skip_bits_long(s, 0);
00409 #endif
00410 }
00411 
00412 static inline void align_get_bits(GetBitContext *s)
00413 {
00414     int n = -get_bits_count(s) & 7;
00415     if (n) skip_bits(s, n);
00416 }
00417 
00418 #define init_vlc(vlc, nb_bits, nb_codes,                \
00419                  bits, bits_wrap, bits_size,            \
00420                  codes, codes_wrap, codes_size,         \
00421                  flags)                                 \
00422         init_vlc_sparse(vlc, nb_bits, nb_codes,         \
00423                         bits, bits_wrap, bits_size,     \
00424                         codes, codes_wrap, codes_size,  \
00425                         NULL, 0, 0, flags)
00426 
00427 int init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
00428              const void *bits, int bits_wrap, int bits_size,
00429              const void *codes, int codes_wrap, int codes_size,
00430              const void *symbols, int symbols_wrap, int symbols_size,
00431              int flags);
00432 #define INIT_VLC_LE         2
00433 #define INIT_VLC_USE_NEW_STATIC 4
00434 void free_vlc(VLC *vlc);
00435 
00436 #define INIT_VLC_STATIC(vlc, bits, a,b,c,d,e,f,g, static_size) do {     \
00437         static VLC_TYPE table[static_size][2];                          \
00438         (vlc)->table = table;                                           \
00439         (vlc)->table_allocated = static_size;                           \
00440         init_vlc(vlc, bits, a,b,c,d,e,f,g, INIT_VLC_USE_NEW_STATIC);    \
00441     } while (0)
00442 
00443 
00450 #define GET_VLC(code, name, gb, table, bits, max_depth) do {    \
00451         int n, nb_bits;                                         \
00452         unsigned int index;                                     \
00453                                                                 \
00454         index = SHOW_UBITS(name, gb, bits);                     \
00455         code  = table[index][0];                                \
00456         n     = table[index][1];                                \
00457                                                                 \
00458         if (max_depth > 1 && n < 0) {                           \
00459             LAST_SKIP_BITS(name, gb, bits);                     \
00460             UPDATE_CACHE(name, gb);                             \
00461                                                                 \
00462             nb_bits = -n;                                       \
00463                                                                 \
00464             index = SHOW_UBITS(name, gb, nb_bits) + code;       \
00465             code  = table[index][0];                            \
00466             n     = table[index][1];                            \
00467             if (max_depth > 2 && n < 0) {                       \
00468                 LAST_SKIP_BITS(name, gb, nb_bits);              \
00469                 UPDATE_CACHE(name, gb);                         \
00470                                                                 \
00471                 nb_bits = -n;                                   \
00472                                                                 \
00473                 index = SHOW_UBITS(name, gb, nb_bits) + code;   \
00474                 code  = table[index][0];                        \
00475                 n     = table[index][1];                        \
00476             }                                                   \
00477         }                                                       \
00478         SKIP_BITS(name, gb, n);                                 \
00479     } while (0)
00480 
00481 #define GET_RL_VLC(level, run, name, gb, table, bits, max_depth, need_update) do { \
00482         int n, nb_bits;                                                 \
00483         unsigned int index;                                             \
00484                                                                         \
00485         index = SHOW_UBITS(name, gb, bits);                             \
00486         level = table[index].level;                                     \
00487         n     = table[index].len;                                       \
00488                                                                         \
00489         if (max_depth > 1 && n < 0) {                                   \
00490             SKIP_BITS(name, gb, bits);                                  \
00491             if (need_update) {                                          \
00492                 UPDATE_CACHE(name, gb);                                 \
00493             }                                                           \
00494                                                                         \
00495             nb_bits = -n;                                               \
00496                                                                         \
00497             index = SHOW_UBITS(name, gb, nb_bits) + level;              \
00498             level = table[index].level;                                 \
00499             n     = table[index].len;                                   \
00500         }                                                               \
00501         run = table[index].run;                                         \
00502         SKIP_BITS(name, gb, n);                                         \
00503     } while (0)
00504 
00505 
00514 static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE (*table)[2],
00515                                   int bits, int max_depth)
00516 {
00517     int code;
00518 
00519     OPEN_READER(re, s);
00520     UPDATE_CACHE(re, s);
00521 
00522     GET_VLC(code, re, s, table, bits, max_depth);
00523 
00524     CLOSE_READER(re, s);
00525     return code;
00526 }
00527 
00528 static inline int decode012(GetBitContext *gb){
00529     int n;
00530     n = get_bits1(gb);
00531     if (n == 0)
00532         return 0;
00533     else
00534         return get_bits1(gb) + 1;
00535 }
00536 
00537 static inline int decode210(GetBitContext *gb){
00538     if (get_bits1(gb))
00539         return 0;
00540     else
00541         return 2 - get_bits1(gb);
00542 }
00543 
00544 static inline int get_bits_left(GetBitContext *gb)
00545 {
00546     return gb->size_in_bits - get_bits_count(gb);
00547 }
00548 
00549 //#define TRACE
00550 
00551 #ifdef TRACE
00552 static inline void print_bin(int bits, int n){
00553     int i;
00554 
00555     for (i = n-1; i >= 0; i--) {
00556         av_log(NULL, AV_LOG_DEBUG, "%d", (bits>>i)&1);
00557     }
00558     for (i = n; i < 24; i++)
00559         av_log(NULL, AV_LOG_DEBUG, " ");
00560 }
00561 
00562 static inline int get_bits_trace(GetBitContext *s, int n, char *file,
00563                                  const char *func, int line){
00564     int r = get_bits(s, n);
00565 
00566     print_bin(r, n);
00567     av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d bit @%5d in %s %s:%d\n",
00568            r, n, r, get_bits_count(s)-n, file, func, line);
00569     return r;
00570 }
00571 static inline int get_vlc_trace(GetBitContext *s, VLC_TYPE (*table)[2],
00572                                 int bits, int max_depth, char *file,
00573                                 const char *func, int line){
00574     int show  = show_bits(s, 24);
00575     int pos   = get_bits_count(s);
00576     int r     = get_vlc2(s, table, bits, max_depth);
00577     int len   = get_bits_count(s) - pos;
00578     int bits2 = show >> (24-len);
00579 
00580     print_bin(bits2, len);
00581 
00582     av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d vlc @%5d in %s %s:%d\n",
00583            bits2, len, r, pos, file, func, line);
00584     return r;
00585 }
00586 static inline int get_xbits_trace(GetBitContext *s, int n, char *file,
00587                                   const char *func, int line){
00588     int show = show_bits(s, n);
00589     int r    = get_xbits(s, n);
00590 
00591     print_bin(show, n);
00592     av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d xbt @%5d in %s %s:%d\n",
00593            show, n, r, get_bits_count(s)-n, file, func, line);
00594     return r;
00595 }
00596 
00597 #define get_bits(s, n)  get_bits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00598 #define get_bits1(s)    get_bits_trace(s, 1, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00599 #define get_xbits(s, n) get_xbits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00600 #define get_vlc(s, vlc)            get_vlc_trace(s, (vlc)->table, (vlc)->bits, 3, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00601 #define get_vlc2(s, tab, bits, max) get_vlc_trace(s, tab, bits, max, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00602 
00603 #define tprintf(p, ...) av_log(p, AV_LOG_DEBUG, __VA_ARGS__)
00604 
00605 #else //TRACE
00606 #define tprintf(p, ...) {}
00607 #endif
00608 
00609 #endif /* AVCODEC_GET_BITS_H */

Generated on Fri Feb 22 2013 07:24:26 for FFmpeg by  doxygen 1.7.1