73 строки
2.1 KiB
C
73 строки
2.1 KiB
C
/*
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* Copyright (c) 2016, 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 <assert.h>
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#include "./aom_config.h"
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#include "aom/aom_integer.h"
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#include "aom_dsp/ans.h"
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#include "aom_dsp/prob.h"
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void aom_rans_build_cdf_from_pdf(const AnsP10 token_probs[], rans_lut cdf_tab) {
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int i;
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cdf_tab[0] = 0;
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for (i = 1; cdf_tab[i - 1] < RANS_PRECISION; ++i) {
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cdf_tab[i] = cdf_tab[i - 1] + token_probs[i - 1];
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}
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assert(cdf_tab[i - 1] == RANS_PRECISION);
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}
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static int find_largest(const AnsP10 *const pdf_tab, int num_syms) {
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int largest_idx = -1;
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int largest_p = -1;
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int i;
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for (i = 0; i < num_syms; ++i) {
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int p = pdf_tab[i];
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if (p > largest_p) {
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largest_p = p;
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largest_idx = i;
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}
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}
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return largest_idx;
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}
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void aom_rans_merge_prob8_pdf(AnsP10 *const out_pdf, const AnsP8 node_prob,
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const AnsP10 *const src_pdf, int in_syms) {
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int i;
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int adjustment = RANS_PRECISION;
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const int round_fact = ANS_P8_PRECISION >> 1;
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const AnsP8 p1 = ANS_P8_PRECISION - node_prob;
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const int out_syms = in_syms + 1;
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assert(src_pdf != out_pdf);
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out_pdf[0] = node_prob << (10 - 8);
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adjustment -= out_pdf[0];
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for (i = 0; i < in_syms; ++i) {
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int p = (p1 * src_pdf[i] + round_fact) >> ANS_P8_SHIFT;
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p = AOMMIN(p, (int)RANS_PRECISION - in_syms);
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p = AOMMAX(p, 1);
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out_pdf[i + 1] = p;
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adjustment -= p;
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}
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// Adjust probabilities so they sum to the total probability
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if (adjustment > 0) {
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i = find_largest(out_pdf, out_syms);
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out_pdf[i] += adjustment;
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} else {
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while (adjustment < 0) {
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i = find_largest(out_pdf, out_syms);
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--out_pdf[i];
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assert(out_pdf[i] > 0);
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adjustment++;
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}
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}
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}
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