The Tor Browser: media/libvpx/vp9/decoder/vp9

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

     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  */

    11 #include "vp9/common/vp9_entropy.h"

    13 #include "vp9/decoder/vp9_dsubexp.h"

    15 static int inv_recenter_nonneg(int v, int m) {

    16   if (v > 2 * m)

    17     return v;

    19   return v % 2 ? m - (v + 1) / 2 : m + v / 2;

    20 }

    22 static int decode_uniform(vp9_reader *r, int n) {

    23   int v;

    24   const int l = get_unsigned_bits(n);

    25   const int m = (1 << l) - n;

    26   if (!l)

    27     return 0;

    29   v = vp9_read_literal(r, l - 1);

    30   return v < m ?  v : (v << 1) - m + vp9_read_bit(r);

    31 }

    34 static int merge_index(int v, int n, int modulus) {

    35   int max1 = (n - 1 - modulus / 2) / modulus + 1;

    36   if (v < max1) {

    37     v = v * modulus + modulus / 2;

    38   } else {

    39     int w;

    40     v -= max1;

    41     w = v;

    42     v += (v + modulus - modulus / 2) / modulus;

    43     while (v % modulus == modulus / 2 ||

    44            w != v - (v + modulus - modulus / 2) / modulus) v++;

    45   }

    46   return v;

    47 }

    49 static int inv_remap_prob(int v, int m) {

    50   static int inv_map_table[MAX_PROB - 1] = {

    51       6,  19,  32,  45,  58,  71,  84,  97, 110, 123, 136, 149, 162, 175, 188,

    52     201, 214, 227, 240, 253,   0,   1,   2,   3,   4,   5,   7,   8,   9,  10,

    53      11,  12,  13,  14,  15,  16,  17,  18,  20,  21,  22,  23,  24,  25,  26,

    54      27,  28,  29,  30,  31,  33,  34,  35,  36,  37,  38,  39,  40,  41,  42,

    55      43,  44,  46,  47,  48,  49,  50,  51,  52,  53,  54,  55,  56,  57,  59,

    56      60,  61,  62,  63,  64,  65,  66,  67,  68,  69,  70,  72,  73,  74,  75,

    57      76,  77,  78,  79,  80,  81,  82,  83,  85,  86,  87,  88,  89,  90,  91,

    58      92,  93,  94,  95,  96,  98,  99, 100, 101, 102, 103, 104, 105, 106, 107,

    59     108, 109, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 124,

    60     125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 137, 138, 139, 140,

    61     141, 142, 143, 144, 145, 146, 147, 148, 150, 151, 152, 153, 154, 155, 156,

    62     157, 158, 159, 160, 161, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172,

    63     173, 174, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 189,

    64     190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 202, 203, 204, 205,

    65     206, 207, 208, 209, 210, 211, 212, 213, 215, 216, 217, 218, 219, 220, 221,

    66     222, 223, 224, 225, 226, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237,

    67     238, 239, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252

    68   };

    69   // The clamp is not necessary for conforming VP9 stream, it is added to

    70   // prevent out of bound access for bad input data

    71   v = clamp(v, 0, 253);

    72   v = inv_map_table[v];

    73   m--;

    74   if ((m << 1) <= MAX_PROB) {

    75     return 1 + inv_recenter_nonneg(v + 1, m);

    76   } else {

    77     return MAX_PROB - inv_recenter_nonneg(v + 1, MAX_PROB - 1 - m);

    78   }

    79 }

    81 static int decode_term_subexp(vp9_reader *r, int k, int num_syms) {

    82   int i = 0, mk = 0, word;

    83   while (1) {

    84     const int b = i ? k + i - 1 : k;

    85     const int a = 1 << b;

    86     if (num_syms <= mk + 3 * a) {

    87       word = decode_uniform(r, num_syms - mk) + mk;

    88       break;

    89     } else {

    90       if (vp9_read_bit(r)) {

    91         i++;

    92         mk += a;

    93       } else {

    94         word = vp9_read_literal(r, b) + mk;

    95         break;

    96       }

    97     }

    98   }

    99   return word;

   100 }

   102 void vp9_diff_update_prob(vp9_reader *r, vp9_prob* p) {

   103   if (vp9_read(r, DIFF_UPDATE_PROB)) {

   104     const int delp = decode_term_subexp(r, SUBEXP_PARAM, 255);

   105     *p = (vp9_prob)inv_remap_prob(delp, *p);

   106   }

   107 }

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