aom_dsp/binary_codes_reader.c

   1 /*
   2  * Copyright (c) 2017, Alliance for Open Media. All rights reserved
   3  *
   4  * This source code is subject to the terms of the BSD 2 Clause License and
   5  * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
   6  * was not distributed with this source code in the LICENSE file, you can
   7  * obtain it at www.aomedia.org/license/software. If the Alliance for Open
   8  * Media Patent License 1.0 was not distributed with this source code in the
   9  * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
  10  */
  11
  12 #include "aom_dsp/binary_codes_reader.h"
  13 #include "aom_dsp/recenter.h"
  14
  15 uint16_t aom_read_primitive_quniform_(aom_reader *r,
  16                                       uint16_t n ACCT_STR_PARAM) {
  17   if (n <= 1) return 0;
  18   const int l = get_msb(n) + 1;
  19   const int m = (1 << l) - n;
  20   const int v = aom_read_literal(r, l - 1, ACCT_STR_NAME);
  21   return v < m ? v : (v << 1) - m + aom_read_bit(r, ACCT_STR_NAME);
  22 }
  23
  24 // Decode finite subexponential code that for a symbol v in [0, n-1] with
  25 // parameter k
  26 uint16_t aom_read_primitive_subexpfin_(aom_reader *r, uint16_t n,
  27                                        uint16_t k ACCT_STR_PARAM) {
  28   int i = 0;
  29   int mk = 0;
  30
  31   while (1) {
  32     int b = (i ? k + i - 1 : k);
  33     int a = (1 << b);
  34
  35     if (n <= mk + 3 * a) {
  36       return aom_read_primitive_quniform(r, n - mk, ACCT_STR_NAME) + mk;
  37     }
  38
  39     if (!aom_read_bit(r, ACCT_STR_NAME)) {
  40       return aom_read_literal(r, b, ACCT_STR_NAME) + mk;
  41     }
  42
  43     i = i + 1;
  44     mk += a;
  45   }
  46
  47   assert(0);
  48   return 0;
  49 }
  50
  51 uint16_t aom_read_primitive_refsubexpfin_(aom_reader *r, uint16_t n, uint16_t k,
  52                                           uint16_t ref ACCT_STR_PARAM) {
  53   return inv_recenter_finite_nonneg(
  54       n, ref, aom_read_primitive_subexpfin(r, n, k, ACCT_STR_NAME));
  55 }