binary_codes_writer.c (3207B)
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/bitwriter.h" 13 #include "aom_dsp/binary_codes_writer.h" 14 #include "aom_dsp/recenter.h" 15 #include "aom_ports/bitops.h" 16 17 // Encodes a value v in [0, n-1] quasi-uniformly 18 static void write_primitive_quniform(aom_writer *w, uint16_t n, uint16_t v) { 19 if (n <= 1) return; 20 const int l = get_msb(n) + 1; 21 const int m = (1 << l) - n; 22 if (v < m) { 23 aom_write_literal(w, v, l - 1); 24 } else { 25 aom_write_literal(w, m + ((v - m) >> 1), l - 1); 26 aom_write_bit(w, (v - m) & 1); 27 } 28 } 29 30 static int count_primitive_quniform(uint16_t n, uint16_t v) { 31 if (n <= 1) return 0; 32 const int l = get_msb(n) + 1; 33 const int m = (1 << l) - n; 34 return v < m ? l - 1 : l; 35 } 36 37 // Finite subexponential code that codes a symbol v in [0, n-1] with parameter k 38 static void write_primitive_subexpfin(aom_writer *w, uint16_t n, uint16_t k, 39 uint16_t v) { 40 int i = 0; 41 int mk = 0; 42 while (1) { 43 int b = (i ? k + i - 1 : k); 44 int a = (1 << b); 45 if (n <= mk + 3 * a) { 46 write_primitive_quniform(w, n - mk, v - mk); 47 break; 48 } else { 49 int t = (v >= mk + a); 50 aom_write_bit(w, t); 51 if (t) { 52 i = i + 1; 53 mk += a; 54 } else { 55 aom_write_literal(w, v - mk, b); 56 break; 57 } 58 } 59 } 60 } 61 62 static int count_primitive_subexpfin(uint16_t n, uint16_t k, uint16_t v) { 63 int count = 0; 64 int i = 0; 65 int mk = 0; 66 while (1) { 67 int b = (i ? k + i - 1 : k); 68 int a = (1 << b); 69 if (n <= mk + 3 * a) { 70 count += count_primitive_quniform(n - mk, v - mk); 71 break; 72 } else { 73 int t = (v >= mk + a); 74 count++; 75 if (t) { 76 i = i + 1; 77 mk += a; 78 } else { 79 count += b; 80 break; 81 } 82 } 83 } 84 return count; 85 } 86 87 // Finite subexponential code that codes a symbol v in [0, n-1] with parameter k 88 // based on a reference ref also in [0, n-1]. 89 // Recenters symbol around r first and then uses a finite subexponential code. 90 void aom_write_primitive_refsubexpfin(aom_writer *w, uint16_t n, uint16_t k, 91 uint16_t ref, uint16_t v) { 92 write_primitive_subexpfin(w, n, k, recenter_finite_nonneg(n, ref, v)); 93 } 94 95 int aom_count_primitive_refsubexpfin(uint16_t n, uint16_t k, uint16_t ref, 96 uint16_t v) { 97 return count_primitive_subexpfin(n, k, recenter_finite_nonneg(n, ref, v)); 98 } 99 100 int aom_count_signed_primitive_refsubexpfin(uint16_t n, uint16_t k, int16_t ref, 101 int16_t v) { 102 ref += n - 1; 103 v += n - 1; 104 const uint16_t scaled_n = (n << 1) - 1; 105 return aom_count_primitive_refsubexpfin(scaled_n, k, ref, v); 106 }