FFmpeg/libavcodec/opus_rc.c

/*
 * Copyright (c) 2012 Andrew D'Addesio
 * Copyright (c) 2013-2014 Mozilla Corporation
 * Copyright (c) 2016 Rostislav Pehlivanov <atomnuker@gmail.com>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "opus_rc.h"

static av_always_inline void opus_rc_dec_normalize(OpusRangeCoder *rc)
{
    while (rc->range <= 1<<23) {
        rc->value = ((rc->value << 8) | (get_bits(&rc->gb, 8) ^ 0xFF)) & ((1u << 31) - 1);
        rc->range          <<= 8;
        rc->total_read_bits += 8;
    }
}

static av_always_inline void opus_rc_dec_update(OpusRangeCoder *rc, uint32_t scale,
                                                uint32_t low, uint32_t high,
                                                uint32_t total)
{
    rc->value -= scale * (total - high);
    rc->range  = low ? scale * (high - low)
                      : rc->range - scale * (total - high);
    opus_rc_dec_normalize(rc);
}

uint32_t ff_opus_rc_dec_cdf(OpusRangeCoder *rc, const uint16_t *cdf)
{
    unsigned int k, scale, total, symbol, low, high;

    total = *cdf++;

    scale   = rc->range / total;
    symbol = rc->value / scale + 1;
    symbol = total - FFMIN(symbol, total);

    for (k = 0; cdf[k] <= symbol; k++);
    high = cdf[k];
    low  = k ? cdf[k-1] : 0;

    opus_rc_dec_update(rc, scale, low, high, total);

    return k;
}

uint32_t ff_opus_rc_dec_log(OpusRangeCoder *rc, uint32_t bits)
{
    uint32_t k, scale;
    scale = rc->range >> bits; // in this case, scale = symbol

    if (rc->value >= scale) {
        rc->value -= scale;
        rc->range -= scale;
        k = 0;
    } else {
        rc->range = scale;
        k = 1;
    }
    opus_rc_dec_normalize(rc);
    return k;
}

/**
 * CELT: read 1-25 raw bits at the end of the frame, backwards byte-wise
 */
uint32_t ff_opus_rc_get_raw(OpusRangeCoder *rc, uint32_t count)
{
    uint32_t value = 0;

    while (rc->rb.bytes && rc->rb.cachelen < count) {
        rc->rb.cacheval |= *--rc->rb.position << rc->rb.cachelen;
        rc->rb.cachelen += 8;
        rc->rb.bytes--;
    }

    value = av_mod_uintp2(rc->rb.cacheval, count);
    rc->rb.cacheval    >>= count;
    rc->rb.cachelen     -= count;
    rc->total_read_bits += count;

    return value;
}

/**
 * CELT: read a uniform distribution
 */
uint32_t ff_opus_rc_dec_uint(OpusRangeCoder *rc, uint32_t size)
{
    uint32_t bits, k, scale, total;

    bits  = opus_ilog(size - 1);
    total = (bits > 8) ? ((size - 1) >> (bits - 8)) + 1 : size;

    scale  = rc->range / total;
    k      = rc->value / scale + 1;
    k      = total - FFMIN(k, total);
    opus_rc_dec_update(rc, scale, k, k + 1, total);

    if (bits > 8) {
        k = k << (bits - 8) | ff_opus_rc_get_raw(rc, bits - 8);
        return FFMIN(k, size - 1);
    } else
        return k;
}

uint32_t ff_opus_rc_dec_uint_step(OpusRangeCoder *rc, int k0)
{
    /* Use a probability of 3 up to itheta=8192 and then use 1 after */
    uint32_t k, scale, symbol, total = (k0+1)*3 + k0;
    scale  = rc->range / total;
    symbol = rc->value / scale + 1;
    symbol = total - FFMIN(symbol, total);

    k = (symbol < (k0+1)*3) ? symbol/3 : symbol - (k0+1)*2;

    opus_rc_dec_update(rc, scale, (k <= k0) ? 3*(k+0) : (k-1-k0) + 3*(k0+1),
                       (k <= k0) ? 3*(k+1) : (k-0-k0) + 3*(k0+1), total);
    return k;
}

uint32_t ff_opus_rc_dec_uint_tri(OpusRangeCoder *rc, int qn)
{
    uint32_t k, scale, symbol, total, low, center;

    total = ((qn>>1) + 1) * ((qn>>1) + 1);
    scale   = rc->range / total;
    center = rc->value / scale + 1;
    center = total - FFMIN(center, total);

    if (center < total >> 1) {
        k      = (ff_sqrt(8 * center + 1) - 1) >> 1;
        low    = k * (k + 1) >> 1;
        symbol = k + 1;
    } else {
        k      = (2*(qn + 1) - ff_sqrt(8*(total - center - 1) + 1)) >> 1;
        low    = total - ((qn + 1 - k) * (qn + 2 - k) >> 1);
        symbol = qn + 1 - k;
    }

    opus_rc_dec_update(rc, scale, low, low + symbol, total);

    return k;
}

int ff_opus_rc_dec_laplace(OpusRangeCoder *rc, uint32_t symbol, int decay)
{
    /* extends the range coder to model a Laplace distribution */
    int value = 0;
    uint32_t scale, low = 0, center;

    scale  = rc->range >> 15;
    center = rc->value / scale + 1;
    center = (1 << 15) - FFMIN(center, 1 << 15);

    if (center >= symbol) {
        value++;
        low = symbol;
        symbol = 1 + ((32768 - 32 - symbol) * (16384-decay) >> 15);

        while (symbol > 1 && center >= low + 2 * symbol) {
            value++;
            symbol *= 2;
            low    += symbol;
            symbol  = (((symbol - 2) * decay) >> 15) + 1;
        }

        if (symbol <= 1) {
            int distance = (center - low) >> 1;
            value += distance;
            low   += 2 * distance;
        }

        if (center < low + symbol)
            value *= -1;
        else
            low += symbol;
    }

    opus_rc_dec_update(rc, scale, low, FFMIN(low + symbol, 32768), 32768);

    return value;
}

int ff_opus_rc_dec_init(OpusRangeCoder *rc, const uint8_t *data, int size)
{
    int ret = init_get_bits8(&rc->gb, data, size);
    if (ret < 0)
        return ret;

    rc->range = 128;
    rc->value = 127 - get_bits(&rc->gb, 7);
    rc->total_read_bits = 9;
    opus_rc_dec_normalize(rc);

    return 0;
}

void ff_opus_rc_dec_raw_init(OpusRangeCoder *rc, const uint8_t *rightend, uint32_t bytes)
{
    rc->rb.position = rightend;
    rc->rb.bytes    = bytes;
    rc->rb.cachelen = 0;
    rc->rb.cacheval = 0;
}