w3d/golomb.h

   1 #ifndef __GOLOMB_H
   2 #define __GOLOMB_H
   3
   4
   5 #include "bitcoder.h"
   6
   7
   8 static inline
   9 unsigned int required_bits (unsigned int x)
  10 {
  11    int bits = 31;
  12
  13    while ((x & (1 << bits)) == 0 && bits)
  14       bits--;
  15
  16    return bits;
  17 }
  18
  19
  20 static inline
  21 void write_number_binary (BitCoderState *b, unsigned int x, int bits, int u)
  22 {
  23 //printf ("wrote %i with %i bits (%i+%i)\n", x, u+bits, u, bits);
  24    while (bits) {
  25       bits--;
  26       bitcoder_write_bit (b, (x >> bits) & 1);
  27    }
  28 }
  29
  30
  31 static inline
  32 unsigned int read_number_binary (BitCoderState *b, int bits)
  33 {
  34    unsigned int x = 0;
  35
  36    while (bits) {
  37       bits--;
  38       x |= bitcoder_read_bit (b) << bits;
  39    }
  40
  41    return x;
  42 }
  43
  44
  45 static inline
  46 void golomb_write_number (BitCoderState *b, unsigned int x, int bits)
  47 {
  48    unsigned int q, r;
  49 int i = 0;
  50
  51    assert (x > 0);
  52
  53    while ((q = (x - 1) >> bits) > 0) {
  54       bitcoder_write_bit (b, 1);   /* fast temporary adaption, write  */
  55       bits++;                      /* unary representation of q       */
  56 i++;
  57    };
  58
  59    bitcoder_write_bit (b, 0);
  60
  61    r = x - 1 - (q << bits);
  62
  63    write_number_binary (b, r, bits, i+1);
  64 }
  65
  66
  67 static inline
  68 unsigned int golomb_read_number (BitCoderState *b, int bits)
  69 {
  70    unsigned int q = 0, r, x;
  71
  72    while (bitcoder_read_bit (b) != 0) {
  73       bits++;
  74    }
  75
  76    r = read_number_binary (b, bits);
  77    x = (q << bits) + r + 1;
  78
  79    return x;
  80 }
  81
  82
  83 typedef struct {
  84    uint8_t count;
  85    uint8_t bits;          /* a 5.3 fixed point integer  */
  86 } GolombAdaptiveCoderState;
  87
  88 #define GOLOMB_ADAPTIVE_CODER_STATE_INITIALIZER { 8<<3, 0 }
  89
  90
  91 static const int golomb_w_tab [] = { 256, 128, 64 };
  92
  93
  94
  95
  96 static inline
  97 void golombcoder_encode_number (GolombAdaptiveCoderState *g,
  98                                 BitCoderState *b,
  99                                 unsigned int x)
 100 {
 101    golomb_write_number (b, x, g->bits >> 3);
 102
 103    g->bits = ((256 - golomb_w_tab[g->count]) * (int) g->bits +
 104                      golomb_w_tab[g->count] * (required_bits(x)<<3)) / 256;
 105    g->count++;
 106
 107    if (g->count > 2)
 108       g->count = 2;
 109 }
 110
 111
 112 static inline
 113 unsigned int golombcoder_decode_number (GolombAdaptiveCoderState *g,
 114                                         BitCoderState *b)
 115 {
 116    unsigned int x;
 117
 118    x = golomb_read_number (b, g->bits >> 3);
 119
 120    g->bits = ((256 - golomb_w_tab[g->count]) * g->bits +
 121                      golomb_w_tab[g->count] * (required_bits(x)<<3)) / 256;
 122    g->count++;
 123
 124    if (g->count > 2)
 125       g->count = 2;
 126
 127    return x;
 128 }
 129
 130
 131 #endif
 132