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 tree_reader_h
13 #define tree_reader_h 1
14
15 #include "treecoder.h"
16
17 #include "dboolhuff.h"
18
19 typedef BOOL_DECODER vp8_reader;
20
21 #define vp8_read vp8dx_decode_bool
22 #define vp8_read_literal vp8_decode_value
23 #define vp8_read_bit( R) vp8_read( R, vp8_prob_half)
24
25
26 /* Intent of tree data structure is to make decoding trivial. */
27
vp8_treed_read(vp8_reader * const r,vp8_tree t,const vp8_prob * const p)28 static int vp8_treed_read(
29 vp8_reader *const r, /* !!! must return a 0 or 1 !!! */
30 vp8_tree t,
31 const vp8_prob *const p
32 )
33 {
34 register vp8_tree_index i = 0;
35
36 while ((i = t[ i + vp8_read(r, p[i>>1])]) > 0) ;
37
38 return -i;
39 }
40
41
42 /* Variant reads a binary number given distributions on each bit.
43 Note that tree is arbitrary; probability of decoding a zero
44 may or may not depend on previously decoded bits. */
45
vp8_treed_read_num(vp8_reader * const r,vp8_tree t,const vp8_prob * const p)46 static int vp8_treed_read_num(
47 vp8_reader *const r, /* !!! must return a 0 or 1 !!! */
48 vp8_tree t,
49 const vp8_prob *const p
50 )
51 {
52 vp8_tree_index i = 0;
53 int v = 0, b;
54
55 do
56 {
57 b = vp8_read(r, p[i>>1]);
58 v = (v << 1) + b;
59 }
60 while ((i = t[i+b]) > 0);
61
62 return v;
63 }
64 #endif /* tree_reader_h */
65