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/*
* Range coder
* Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
*
* 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
*/
/**
* @file
* Range coder.
* based upon
* "Range encoding: an algorithm for removing redundancy from a digitised
* message.
* G. N. N. Martin Presented in March 1979 to the Video &
* Data Recording Conference,
* IBM UK Scientific Center held in Southampton July 24-27 1979."
*/
#include <string.h>
#include "libavutil/attributes.h"
#include "libavutil/avassert.h"
#include "libavutil/intreadwrite.h"
#include "avcodec.h"
#include "rangecoder.h"
av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
{
c->bytestream_start =
c->bytestream = buf;
c->bytestream_end = buf + buf_size;
c->low = 0;
c->range = 0xFF00;
c->outstanding_count = 0;
c->outstanding_byte = -1;
}
av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf,
int buf_size)
{
/* cast to avoid compiler warning */
ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
c->low = AV_RB16(c->bytestream);
c->bytestream += 2;
if (c->low >= 0xFF00) {
c->low = 0xFF00;
c->bytestream_end = c->bytestream + 2;
}
}
void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
{
const int64_t one = 1LL << 32;
int64_t p;
int last_p8, p8, i;
memset(c->zero_state, 0, sizeof(c->zero_state));
memset(c->one_state, 0, sizeof(c->one_state));
last_p8 = 0;
p = one / 2;
for (i = 0; i < 128; i++) {
p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
if (p8 <= last_p8)
p8 = last_p8 + 1;
if (last_p8 && last_p8 < 256 && p8 <= max_p)
c->one_state[last_p8] = p8;
p += ((one - p) * factor + one / 2) >> 32;
last_p8 = p8;
}
for (i = 256 - max_p; i <= max_p; i++) {
if (c->one_state[i])
continue;
p = (i * one + 128) >> 8;
p += ((one - p) * factor + one / 2) >> 32;
p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
if (p8 <= i)
p8 = i + 1;
if (p8 > max_p)
p8 = max_p;
c->one_state[i] = p8;
}
for (i = 1; i < 255; i++)
c->zero_state[i] = 256 - c->one_state[256 - i];
}
/* Return the number of bytes written. */
int ff_rac_terminate(RangeCoder *c)
{
c->range = 0xFF;
c->low += 0xFF;
renorm_encoder(c);
c->range = 0xFF;
renorm_encoder(c);
av_assert1(c->low == 0);
av_assert1(c->range >= 0x100);
return c->bytestream - c->bytestream_start;
}
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