vp8/encoder/treewriter.h

   1 /*
   2  *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
   3  *
   4  *  Use of this source code is governed by a BSD-style license
   5  *  that can be found in the LICENSE file in the root of the source
   6  *  tree. An additional intellectual property rights grant can be found
   7  *  in the file PATENTS.  All contributing project authors may
   8  *  be found in the AUTHORS file in the root of the source tree.
   9  */
  10
  11
  12 #ifndef __INC_TREEWRITER_H
  13 #define __INC_TREEWRITER_H
  14
  15 /* Trees map alphabets into huffman-like codes suitable for an arithmetic
  16    bit coder.  Timothy S Murphy  11 October 2004 */
  17
  18 #include "treecoder.h"
  19
  20 #include "boolhuff.h"       /* for now */
  21
  22 typedef BOOL_CODER vp8_writer;
  23
  24 #define vp8_write vp8_encode_bool
  25 #define vp8_write_literal vp8_encode_value
  26 #define vp8_write_bit( W, V) vp8_write( W, V, vp8_prob_half)
  27
  28 #define vp8bc_write vp8bc_write_bool
  29 #define vp8bc_write_literal vp8bc_write_bits
  30 #define vp8bc_write_bit( W, V) vp8bc_write_bits( W, V, 1)
  31
  32
  33 /* Approximate length of an encoded bool in 256ths of a bit at given prob */
  34
  35 #define vp8_cost_zero( x) ( vp8_prob_cost[x])
  36 #define vp8_cost_one( x)  vp8_cost_zero( vp8_complement(x))
  37
  38 #define vp8_cost_bit( x, b) vp8_cost_zero( (b)?  vp8_complement(x) : (x) )
  39
  40 /* VP8BC version is scaled by 2^20 rather than 2^8; see bool_coder.h */
  41
  42
  43 /* Both of these return bits, not scaled bits. */
  44
  45 static __inline unsigned int vp8_cost_branch(const unsigned int ct[2], vp8_prob p)
  46 {
  47     /* Imitate existing calculation */
  48
  49     return ((ct[0] * vp8_cost_zero(p))
  50             + (ct[1] * vp8_cost_one(p))) >> 8;
  51 }
  52
  53 /* Small functions to write explicit values and tokens, as well as
  54    estimate their lengths. */
  55
  56 static __inline void vp8_treed_write
  57 (
  58     vp8_writer *const w,
  59     vp8_tree t,
  60     const vp8_prob *const p,
  61     int v,
  62     int n               /* number of bits in v, assumed nonzero */
  63 )
  64 {
  65     vp8_tree_index i = 0;
  66
  67     do
  68     {
  69         const int b = (v >> --n) & 1;
  70         vp8_write(w, b, p[i>>1]);
  71         i = t[i+b];
  72     }
  73     while (n);
  74 }
  75 static __inline void vp8_write_token
  76 (
  77     vp8_writer *const w,
  78     vp8_tree t,
  79     const vp8_prob *const p,
  80     vp8_token *const x
  81 )
  82 {
  83     vp8_treed_write(w, t, p, x->value, x->Len);
  84 }
  85
  86 static __inline int vp8_treed_cost(
  87     vp8_tree t,
  88     const vp8_prob *const p,
  89     int v,
  90     int n               /* number of bits in v, assumed nonzero */
  91 )
  92 {
  93     int c = 0;
  94     vp8_tree_index i = 0;
  95
  96     do
  97     {
  98         const int b = (v >> --n) & 1;
  99         c += vp8_cost_bit(p[i>>1], b);
 100         i = t[i+b];
 101     }
 102     while (n);
 103
 104     return c;
 105 }
 106 static __inline int vp8_cost_token
 107 (
 108     vp8_tree t,
 109     const vp8_prob *const p,
 110     vp8_token *const x
 111 )
 112 {
 113     return vp8_treed_cost(t, p, x->value, x->Len);
 114 }
 115
 116 /* Fill array of costs for all possible token values. */
 117
 118 void vp8_cost_tokens(
 119     int *Costs, const vp8_prob *, vp8_tree
 120 );
 121
 122 #endif