138 lines
4.2 KiB
C
138 lines
4.2 KiB
C
/*
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* Copyright (c) 2017, Alliance for Open Media. All rights reserved
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*
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* This source code is subject to the terms of the BSD 2 Clause License and
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* the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
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* was not distributed with this source code in the LICENSE file, you can
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* obtain it at www.aomedia.org/license/software. If the Alliance for Open
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* Media Patent License 1.0 was not distributed with this source code in the
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* PATENTS file, you can obtain it at www.aomedia.org/license/patent.
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*/
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#include "aom_dsp/bitwriter.h"
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#include "aom_dsp/binary_codes_writer.h"
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#include "aom_dsp/recenter.h"
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#include "aom_ports/bitops.h"
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// Codes a symbol v in [-2^mag_bits, 2^mag_bits].
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// mag_bits is number of bits for magnitude. The alphabet is of size
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// 2 * 2^mag_bits + 1, symmetric around 0, where one bit is used to
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// indicate 0 or non-zero, mag_bits bits are used to indicate magnitide
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// and 1 more bit for the sign if non-zero.
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void aom_write_primitive_symmetric(aom_writer *w, int16_t v,
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unsigned int abs_bits) {
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if (v == 0) {
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aom_write_bit(w, 0);
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} else {
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const int x = abs(v);
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const int s = v < 0;
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aom_write_bit(w, 1);
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aom_write_bit(w, s);
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aom_write_literal(w, x - 1, abs_bits);
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}
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}
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int aom_count_primitive_symmetric(int16_t v, unsigned int abs_bits) {
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return (v == 0 ? 1 : abs_bits + 2);
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}
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// Encodes a value v in [0, n-1] quasi-uniformly
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void aom_write_primitive_quniform(aom_writer *w, uint16_t n, uint16_t v) {
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if (n <= 1) return;
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const int l = get_msb(n) + 1;
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const int m = (1 << l) - n;
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if (v < m) {
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aom_write_literal(w, v, l - 1);
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} else {
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aom_write_literal(w, m + ((v - m) >> 1), l - 1);
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aom_write_bit(w, (v - m) & 1);
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}
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}
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int aom_count_primitive_quniform(uint16_t n, uint16_t v) {
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if (n <= 1) return 0;
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const int l = get_msb(n) + 1;
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const int m = (1 << l) - n;
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return v < m ? l - 1 : l;
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}
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// Finite subexponential code that codes a symbol v in [0, n-1] with parameter k
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void aom_write_primitive_subexpfin(aom_writer *w, uint16_t n, uint16_t k,
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uint16_t v) {
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int i = 0;
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int mk = 0;
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while (1) {
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int b = (i ? k + i - 1 : k);
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int a = (1 << b);
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if (n <= mk + 3 * a) {
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aom_write_primitive_quniform(w, n - mk, v - mk);
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break;
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} else {
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int t = (v >= mk + a);
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aom_write_bit(w, t);
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if (t) {
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i = i + 1;
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mk += a;
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} else {
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aom_write_literal(w, v - mk, b);
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break;
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}
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}
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}
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}
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int aom_count_primitive_subexpfin(uint16_t n, uint16_t k, uint16_t v) {
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int count = 0;
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int i = 0;
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int mk = 0;
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while (1) {
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int b = (i ? k + i - 1 : k);
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int a = (1 << b);
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if (n <= mk + 3 * a) {
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count += aom_count_primitive_quniform(n - mk, v - mk);
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break;
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} else {
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int t = (v >= mk + a);
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count++;
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if (t) {
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i = i + 1;
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mk += a;
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} else {
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count += b;
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break;
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}
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}
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}
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return count;
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}
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// Finite subexponential code that codes a symbol v in [0, n-1] with parameter k
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// based on a reference ref also in [0, n-1].
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// Recenters symbol around r first and then uses a finite subexponential code.
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void aom_write_primitive_refsubexpfin(aom_writer *w, uint16_t n, uint16_t k,
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uint16_t ref, uint16_t v) {
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aom_write_primitive_subexpfin(w, n, k, recenter_finite_nonneg(n, ref, v));
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}
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void aom_write_signed_primitive_refsubexpfin(aom_writer *w, uint16_t n,
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uint16_t k, int16_t ref,
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int16_t v) {
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ref += n - 1;
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v += n - 1;
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const uint16_t scaled_n = (n << 1) - 1;
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aom_write_primitive_refsubexpfin(w, scaled_n, k, ref, v);
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}
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int aom_count_primitive_refsubexpfin(uint16_t n, uint16_t k, uint16_t ref,
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uint16_t v) {
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return aom_count_primitive_subexpfin(n, k, recenter_finite_nonneg(n, ref, v));
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}
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int aom_count_signed_primitive_refsubexpfin(uint16_t n, uint16_t k, int16_t ref,
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int16_t v) {
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ref += n - 1;
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v += n - 1;
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const uint16_t scaled_n = (n << 1) - 1;
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return aom_count_primitive_refsubexpfin(scaled_n, k, ref, v);
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}
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