ref: 343acaa8f2233acfe427a8e3557efa7bae092d77
dir: /vp9/decoder/vp9_dsubexp.c/
/*
Copyright (c) 2010 The WebM project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "vp9/common/vp9_entropy.h"
#include "vp9/decoder/vp9_dsubexp.h"
static int inv_recenter_nonneg(int v, int m) {
if (v > 2 * m)
return v;
return v % 2 ? m - (v + 1) / 2 : m + v / 2;
}
static int decode_uniform(vp9_reader *r) {
const int l = 8;
const int m = (1 << l) - 191;
const int v = vp9_read_literal(r, l - 1);
return v < m ? v : (v << 1) - m + vp9_read_bit(r);
}
static int inv_remap_prob(int v, int m) {
static int inv_map_table[MAX_PROB - 1] = {
6, 19, 32, 45, 58, 71, 84, 97, 110, 123, 136, 149, 162, 175, 188,
201, 214, 227, 240, 253, 0, 1, 2, 3, 4, 5, 7, 8, 9, 10,
11, 12, 13, 14, 15, 16, 17, 18, 20, 21, 22, 23, 24, 25, 26,
27, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
43, 44, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 59,
60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 72, 73, 74, 75,
76, 77, 78, 79, 80, 81, 82, 83, 85, 86, 87, 88, 89, 90, 91,
92, 93, 94, 95, 96, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107,
108, 109, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 124,
125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 137, 138, 139, 140,
141, 142, 143, 144, 145, 146, 147, 148, 150, 151, 152, 153, 154, 155, 156,
157, 158, 159, 160, 161, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172,
173, 174, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 189,
190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 202, 203, 204, 205,
206, 207, 208, 209, 210, 211, 212, 213, 215, 216, 217, 218, 219, 220, 221,
222, 223, 224, 225, 226, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237,
238, 239, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252
};
// The clamp is not necessary for conforming VP9 stream, it is added to
// prevent out of bound access for bad input data
v = clamp(v, 0, 253);
v = inv_map_table[v];
m--;
if ((m << 1) <= MAX_PROB) {
return 1 + inv_recenter_nonneg(v + 1, m);
} else {
return MAX_PROB - inv_recenter_nonneg(v + 1, MAX_PROB - 1 - m);
}
}
static int decode_term_subexp(vp9_reader *r) {
if (!vp9_read_bit(r))
return vp9_read_literal(r, 4);
if (!vp9_read_bit(r))
return vp9_read_literal(r, 4) + 16;
if (!vp9_read_bit(r))
return vp9_read_literal(r, 5) + 32;
return decode_uniform(r) + 64;
}
void vp9_diff_update_prob(vp9_reader *r, vp9_prob* p) {
if (vp9_read(r, DIFF_UPDATE_PROB)) {
const int delp = decode_term_subexp(r);
*p = (vp9_prob)inv_remap_prob(delp, *p);
}
}