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 /** Structure for bistream I/O. */
  18 struct getbit_context {
  19         /* Start of the internal buffer. */
  20         const uint8_t *buffer;
  21         /* End of the internal buffer. */
  22         const uint8_t *buffer_end;
  23         /** Bit counter. */
  24         int index;
  25 };
  26
  27 #define VLC_TYPE int16_t
  28
  29 struct vlc {
  30         int bits;
  31         VLC_TYPE(*table)[2];    ///< code, bits
  32         int table_size, table_allocated;
  33 };
  34
  35 /** Load \a gb into local variables. */
  36 #define OPEN_READER(name, gb)\
  37         int name##_index= (gb)->index;\
  38         int name##_cache= 0;\
  39
  40 /** Store local vars in gb. */
  41 #define CLOSE_READER(name, gb)\
  42         (gb)->index= name##_index;\
  43
  44 /**
  45  * Refill the internal cache from the bitstream.
  46  */
  47 #define UPDATE_CACHE(name, gb)\
  48         name##_cache= AV_RB32( ((gb)->buffer) \
  49                 + (name##_index >> 3) ) << (name##_index & 0x07);\
  50
  51 /**
  52  * Remove the next num bits from the cache.
  53  *
  54  * SKIP_COUNTER MUST be called before UPDATE_CACHE / CLOSE_READER).
  55  */
  56 #define SKIP_CACHE(name, gb, num)\
  57         name##_cache <<= (num);
  58
  59 /**
  60  * Increment the internal bit counter.
  61  *
  62  * \sa SKIP_CACHE.
  63  */
  64 #define SKIP_COUNTER(name, gb, num)\
  65         name##_index += (num);\
  66
  67 /** Return the next num bits. */
  68 #define SHOW_UBITS(name, gb, num) \
  69         (((uint32_t)(name##_cache)) >> (32 - (num)))
  70
  71 static inline int get_bits_count(struct getbit_context *s)
  72 {
  73         return s->index;
  74 }
  75
  76 /**
  77  * Read 1-17 bits.
  78  */
  79 static inline unsigned int get_bits(struct getbit_context *s, int n)
  80 {
  81         register int tmp;
  82         OPEN_READER(re, s)
  83         UPDATE_CACHE(re, s)
  84         tmp = SHOW_UBITS(re, s, n);
  85         SKIP_COUNTER(re, s, n)
  86         CLOSE_READER(re, s)
  87         return tmp;
  88 }
  89
  90 static inline void skip_bits(struct getbit_context *s, int n)
  91 {
  92         s->index += n;
  93 }
  94
  95 static inline unsigned int get_bits1(struct getbit_context *s)
  96 {
  97         int idx = s->index;
  98         uint8_t result = s->buffer[idx >> 3];
  99
 100         result <<= (idx & 0x07);
 101         result >>= 8 - 1;
 102         idx++;
 103         s->index = idx;
 104         return result;
 105 }
 106
 107 /**
 108  * Initialize a getbit_context structure.
 109  *
 110  * \param buffer The bitstream buffer. It must be FF_INPUT_BUFFER_PADDING_SIZE
 111  * bytes larger then the actual read bits * because some optimized bitstream
 112  * readers read 32 or 64 bit at once and could read over the end.
 113  *
 114  * \param bit_size The size of the buffer in bytes.
 115  */
 116 static inline void init_get_bits(struct getbit_context *s,
 117                 const uint8_t *buffer, int size)
 118 {
 119         s->buffer = buffer;
 120         s->buffer_end = buffer + size;
 121         s->index = 0;
 122 }
 123
 124 void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
 125                 const void *codes, int codes_size);
 126
 127 void free_vlc(struct vlc *vlc);
 128
 129 /**
 130  * Parse a vlc code.
 131  *
 132  * \param bits The number of bits which will be read at once, must be
 133  * identical to nb_bits in init_vlc()
 134  *
 135  * \param max_depth The number of times bits bits must be read to completely
 136  * read the longest vlc code = (max_vlc_length + bits - 1) / bits.
 137  */
 138 static inline int get_vlc(struct getbit_context *gb, VLC_TYPE(*table)[2],
 139                 int bits, int max_depth)
 140 {
 141         int n, idx, nb_bits, code;
 142
 143         OPEN_READER(re, gb)
 144         UPDATE_CACHE(re, gb)
 145         idx = SHOW_UBITS(re, gb, bits);
 146         code = table[idx][0];
 147         n = table[idx][1];
 148         if (max_depth > 1 && n < 0) {
 149                 SKIP_COUNTER(re, gb, bits)
 150                 UPDATE_CACHE(re, gb)
 151                 nb_bits = -n;
 152                 idx = SHOW_UBITS(re, gb, nb_bits) + code;
 153                 code = table[idx][0];
 154                 n = table[idx][1];
 155                 if (max_depth > 2 && n < 0) {
 156                         SKIP_COUNTER(re, gb, nb_bits)
 157                         UPDATE_CACHE(re, gb)
 158                         nb_bits = -n;
 159                         idx = SHOW_UBITS(re, gb, nb_bits) + code;
 160                         code = table[idx][0];
 161                         n = table[idx][1];
 162                 }
 163         }
 164         SKIP_CACHE(re, gb, n)
 165         SKIP_COUNTER(re, gb, n)
 166         CLOSE_READER(re, gb)
 167         return code;
 168 }