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https://repo.dactyloidae.xyz/Dactyloidae/UXP.git
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edc8d83307
This is the reference implementation for the Alliance for Open Media's av1 video code. The commit used was 4d668d7feb1f8abd809d1bca0418570a7f142a36.
110 lines
3.6 KiB
C
110 lines
3.6 KiB
C
/*
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* Copyright (c) 2001-2016, 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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/* clang-format off */
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#ifdef HAVE_CONFIG_H
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# include "config.h"
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#endif
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#include <stdio.h>
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#include "aom_dsp/bitreader.h"
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#include "av1/common/generic_code.h"
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#include "av1/common/odintrin.h"
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#include "pvq_decoder.h"
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/** Decodes a value from 0 to N-1 (with N up to 16) based on a cdf and adapts
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* the cdf accordingly.
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*
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* @param [in,out] r multi-symbol entropy decoder
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* @param [in,out] cdf CDF of the variable (Q15)
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* @param [in] n number of values possible
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* @param [in,out] count number of symbols encoded with that cdf so far
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* @param [in] rate adaptation rate shift (smaller is faster)
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* @return decoded variable
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*/
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int aom_decode_cdf_adapt_q15_(aom_reader *r, uint16_t *cdf, int n,
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int *count, int rate ACCT_STR_PARAM) {
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int val;
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int i;
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if (*count == 0) {
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int ft;
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ft = cdf[n - 1];
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for (i = 0; i < n; i++) {
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cdf[i] = AOM_ICDF(cdf[i]*32768/ft);
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}
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}
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val = aom_read_cdf(r, cdf, n, ACCT_STR_NAME);
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aom_cdf_adapt_q15(val, cdf, n, count, rate);
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return val;
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}
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/** Encodes a random variable using a "generic" model, assuming that the
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* distribution is one-sided (zero and up), has a single mode, and decays
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* exponentially past the model.
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*
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* @param [in,out] r multi-symbol entropy decoder
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* @param [in,out] model generic probability model
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* @param [in] x variable being encoded
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* @param [in,out] ExQ16 expectation of x (adapted)
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* @param [in] integration integration period of ExQ16 (leaky average over
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* 1<<integration samples)
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*
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* @retval decoded variable x
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*/
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int generic_decode_(aom_reader *r, generic_encoder *model,
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int *ex_q16, int integration ACCT_STR_PARAM) {
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int lg_q1;
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int shift;
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int id;
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uint16_t *cdf;
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int xs;
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int lsb;
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int x;
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lsb = 0;
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lg_q1 = log_ex(*ex_q16);
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/* If expectation is too large, shift x to ensure that
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all we have past xs=15 is the exponentially decaying tail
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of the distribution. */
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shift = OD_MAXI(0, (lg_q1 - 5) >> 1);
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/* Choose the cdf to use: we have two per "octave" of ExQ16. */
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id = OD_MINI(GENERIC_TABLES - 1, lg_q1);
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cdf = model->cdf[id];
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xs = aom_read_symbol_pvq(r, cdf, 16, ACCT_STR_NAME);
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if (xs == 15) {
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int e;
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unsigned decay;
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/* Estimate decay based on the assumption that the distribution is close
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to Laplacian for large values. We should probably have an adaptive
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estimate instead. Note: The 2* is a kludge that's not fully understood
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yet. */
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OD_ASSERT(*ex_q16 < INT_MAX >> 1);
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e = ((2**ex_q16 >> 8) + (1 << shift >> 1)) >> shift;
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decay = OD_MAXI(2, OD_MINI(254, 256*e/(e + 256)));
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xs += aom_laplace_decode_special(r, decay, ACCT_STR_NAME);
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}
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if (shift != 0) {
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int special;
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/* Because of the rounding, there's only half the number of possibilities
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for xs=0 */
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special = xs == 0;
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if (shift - special > 0) {
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lsb = aom_read_literal(r, shift - special, ACCT_STR_NAME);
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}
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lsb -= !special << (shift - 1);
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}
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x = (xs << shift) + lsb;
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generic_model_update(ex_q16, x, integration);
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OD_LOG((OD_LOG_ENTROPY_CODER, OD_LOG_DEBUG,
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"dec: %d %d %d %d %d %x", *ex_q16, x, shift, id, xs, dec->rng));
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return x;
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}
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