ref: 575a083bcc74b8768924da0a823637b9b44f7393
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, int n) { int v; const int l = get_unsigned_bits(n); const int m = (1 << l) - n; if (!l) return 0; v = vp9_read_literal(r, l - 1); return v < m ? v : (v << 1) - m + vp9_read_bit(r); } static int merge_index(int v, int n, int modulus) { int max1 = (n - 1 - modulus / 2) / modulus + 1; if (v < max1) { v = v * modulus + modulus / 2; } else { int w; v -= max1; w = v; v += (v + modulus - modulus / 2) / modulus; while (v % modulus == modulus / 2 || w != v - (v + modulus - modulus / 2) / modulus) v++; } return v; } 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, int k, int num_syms) { int i = 0, mk = 0, word; while (1) { const int b = i ? k + i - 1 : k; const int a = 1 << b; if (num_syms <= mk + 3 * a) { word = decode_uniform(r, num_syms - mk) + mk; break; } else { if (vp9_read_bit(r)) { i++; mk += a; } else { word = vp9_read_literal(r, b) + mk; break; } } } return word; } 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, SUBEXP_PARAM, 255); *p = (vp9_prob)inv_remap_prob(delp, *p); } }