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
write_primitive_quniform(aom_writer * w,uint16_t n,uint16_t v)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
count_primitive_quniform(uint16_t n,uint16_t v)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
write_primitive_subexpfin(aom_writer * w,uint16_t n,uint16_t k,uint16_t v)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
count_primitive_subexpfin(uint16_t n,uint16_t k,uint16_t v)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.
aom_write_primitive_refsubexpfin(aom_writer * w,uint16_t n,uint16_t k,uint16_t ref,uint16_t v)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
aom_count_primitive_refsubexpfin(uint16_t n,uint16_t k,uint16_t ref,uint16_t v)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
aom_count_signed_primitive_refsubexpfin(uint16_t n,uint16_t k,int16_t ref,int16_t v)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 }
107