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 static inline void skip_bits(struct getbit_context *s, int n)
 107 {
 108         /* gcc seems to optimize this to s->index+=n for the ALT_READER :)) */
 109         OPEN_READER(re, s)
 110         UPDATE_CACHE(re, s)
 111         LAST_SKIP_BITS(re, s, n)
 112         CLOSE_READER(re, s)
 113 }
 114
 115 static inline unsigned int get_bits1(struct getbit_context *s)
 116 {
 117         int idx = s->index;
 118         uint8_t result = s->buffer[idx >> 3];
 119
 120         result <<= (idx & 0x07);
 121         result >>= 8 - 1;
 122         idx++;
 123         s->index = idx;
 124         return result;
 125 }
 126
 127 /**
 128  * Initialize a getbit_context structure.
 129  *
 130  * \param buffer The bitstream buffer. It must be FF_INPUT_BUFFER_PADDING_SIZE
 131  * bytes larger then the actual read bits * because some optimized bitstream
 132  * readers read 32 or 64 bit at once and could read over the end.
 133  *
 134  * \param bit_size The size of the buffer in bits.
 135  */
 136 static inline void init_get_bits(struct getbit_context *s,
 137                 const uint8_t *buffer, int bit_size)
 138 {
 139         int buffer_size = (bit_size + 7) >> 3;
 140         if (buffer_size < 0 || bit_size < 0) {
 141                 buffer_size = bit_size = 0;
 142                 buffer = NULL;
 143         }
 144         s->buffer = buffer;
 145         s->buffer_end = buffer + buffer_size;
 146         s->index = 0;
 147 }
 148
 149 void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
 150                 const void *codes, int codes_size);
 151
 152 void free_vlc(struct vlc *vlc);
 153
 154 /**
 155  * Parse a vlc code.
 156  *
 157  * \param bits The number of bits which will be read at once, must be
 158  * identical to nb_bits in init_vlc()
 159  *
 160  * \param max_depth The number of times bits bits must be read to completely
 161  * read the longest vlc code = (max_vlc_length + bits - 1) / bits.
 162  */
 163 static inline int get_vlc(struct getbit_context *gb, VLC_TYPE(*table)[2],
 164                 int bits, int max_depth)
 165 {
 166         int n, idx, nb_bits, code;
 167
 168         OPEN_READER(re, gb)
 169         UPDATE_CACHE(re, gb)
 170         idx = SHOW_UBITS(re, gb, bits);
 171         code = table[idx][0];
 172         n = table[idx][1];
 173         if (max_depth > 1 && n < 0) {
 174                 LAST_SKIP_BITS(re, gb, bits)
 175                 UPDATE_CACHE(re, gb)
 176                 nb_bits = -n;
 177                 idx = SHOW_UBITS(re, gb, nb_bits) + code;
 178                 code = table[idx][0];
 179                 n = table[idx][1];
 180                 if (max_depth > 2 && n < 0) {
 181                         LAST_SKIP_BITS(re, gb, nb_bits)
 182                         UPDATE_CACHE(re, gb)
 183                         nb_bits = -n;
 184                         idx = SHOW_UBITS(re, gb, nb_bits) + code;
 185                         code = table[idx][0];
 186                         n = table[idx][1];
 187                 }
 188         }
 189         SKIP_BITS(re, gb, n)
 190         CLOSE_READER(re, gb)
 191         return code;
 192 }