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 #include "vp9/common/vp9_entropy.h"
12
13 #include "vp9/decoder/vp9_dsubexp.h"
14
inv_recenter_nonneg(int v,int m)15 static int inv_recenter_nonneg(int v, int m) {
16 if (v > 2 * m)
17 return v;
18
19 return v % 2 ? m - (v + 1) / 2 : m + v / 2;
20 }
21
decode_uniform(vp9_reader * r)22 static int decode_uniform(vp9_reader *r) {
23 const int l = 8;
24 const int m = (1 << l) - 191;
25 const int v = vp9_read_literal(r, l - 1);
26 return v < m ? v : (v << 1) - m + vp9_read_bit(r);
27 }
28
inv_remap_prob(int v,int m)29 static int inv_remap_prob(int v, int m) {
30 static int inv_map_table[MAX_PROB - 1] = {
31 6, 19, 32, 45, 58, 71, 84, 97, 110, 123, 136, 149, 162, 175, 188,
32 201, 214, 227, 240, 253, 0, 1, 2, 3, 4, 5, 7, 8, 9, 10,
33 11, 12, 13, 14, 15, 16, 17, 18, 20, 21, 22, 23, 24, 25, 26,
34 27, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
35 43, 44, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 59,
36 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 72, 73, 74, 75,
37 76, 77, 78, 79, 80, 81, 82, 83, 85, 86, 87, 88, 89, 90, 91,
38 92, 93, 94, 95, 96, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107,
39 108, 109, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 124,
40 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 137, 138, 139, 140,
41 141, 142, 143, 144, 145, 146, 147, 148, 150, 151, 152, 153, 154, 155, 156,
42 157, 158, 159, 160, 161, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172,
43 173, 174, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 189,
44 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 202, 203, 204, 205,
45 206, 207, 208, 209, 210, 211, 212, 213, 215, 216, 217, 218, 219, 220, 221,
46 222, 223, 224, 225, 226, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237,
47 238, 239, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252
48 };
49 // The clamp is not necessary for conforming VP9 stream, it is added to
50 // prevent out of bound access for bad input data
51 v = clamp(v, 0, 253);
52 v = inv_map_table[v];
53 m--;
54 if ((m << 1) <= MAX_PROB) {
55 return 1 + inv_recenter_nonneg(v + 1, m);
56 } else {
57 return MAX_PROB - inv_recenter_nonneg(v + 1, MAX_PROB - 1 - m);
58 }
59 }
60
decode_term_subexp(vp9_reader * r)61 static int decode_term_subexp(vp9_reader *r) {
62 if (!vp9_read_bit(r))
63 return vp9_read_literal(r, 4);
64 if (!vp9_read_bit(r))
65 return vp9_read_literal(r, 4) + 16;
66 if (!vp9_read_bit(r))
67 return vp9_read_literal(r, 5) + 32;
68 return decode_uniform(r) + 64;
69 }
70
vp9_diff_update_prob(vp9_reader * r,vp9_prob * p)71 void vp9_diff_update_prob(vp9_reader *r, vp9_prob* p) {
72 if (vp9_read(r, DIFF_UPDATE_PROB)) {
73 const int delp = decode_term_subexp(r);
74 *p = (vp9_prob)inv_remap_prob(delp, *p);
75 }
76 }
77