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      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 "vp8/common/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 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 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 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 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 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 void vp8_cost_tokens2(
    123     int *Costs, const vp8_prob *, vp8_tree, int
    124 );
    125 
    126 #endif
    127