ref: bd775bfda96d8a3675859bda13cb860079b4daf4
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 <assert.h>
#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 & 1) ? m - ((v + 1) >> 1) : m + (v >> 1);
}
static int decode_uniform(vpx_reader *r) {
const int l = 8;
const int m = (1 << l) - 191;
const int v = vpx_read_literal(r, l - 1);
return v < m ? v : (v << 1) - m + vpx_read_bit(r);
}
static int inv_remap_prob(int v, int m) {
static uint8_t inv_map_table[MAX_PROB] = {
7, 20, 33, 46, 59, 72, 85, 98, 111, 124, 137, 150, 163, 176, 189,
202, 215, 228, 241, 254, 1, 2, 3, 4, 5, 6, 8, 9, 10, 11,
12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 24, 25, 26, 27,
28, 29, 30, 31, 32, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43,
44, 45, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 60,
61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76,
77, 78, 79, 80, 81, 82, 83, 84, 86, 87, 88, 89, 90, 91, 92,
93, 94, 95, 96, 97, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108,
109, 110, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 125,
126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 138, 139, 140, 141,
142, 143, 144, 145, 146, 147, 148, 149, 151, 152, 153, 154, 155, 156, 157,
158, 159, 160, 161, 162, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173,
174, 175, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 190,
191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 203, 204, 205, 206,
207, 208, 209, 210, 211, 212, 213, 214, 216, 217, 218, 219, 220, 221, 222,
223, 224, 225, 226, 227, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238,
239, 240, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 253
};
assert(v < (int)(sizeof(inv_map_table) / sizeof(inv_map_table[0])));
v = inv_map_table[v];
m--;
if ((m << 1) <= MAX_PROB) {
return 1 + inv_recenter_nonneg(v, m);
} else {
return MAX_PROB - inv_recenter_nonneg(v, MAX_PROB - 1 - m);
}
}
static int decode_term_subexp(vpx_reader *r) {
if (!vpx_read_bit(r)) return vpx_read_literal(r, 4);
if (!vpx_read_bit(r)) return vpx_read_literal(r, 4) + 16;
if (!vpx_read_bit(r)) return vpx_read_literal(r, 5) + 32;
return decode_uniform(r) + 64;
}
void vp9_diff_update_prob(vpx_reader *r, vpx_prob *p) {
if (vpx_read(r, DIFF_UPDATE_PROB)) {
const int delp = decode_term_subexp(r);
*p = (vpx_prob)inv_remap_prob(delp, *p);
}
}