mirror of
https://github.com/FFmpeg/FFmpeg.git
synced 2024-12-07 11:13:41 +02:00
122 lines
3.4 KiB
C
122 lines
3.4 KiB
C
/*
|
|
* 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;
|
|
c->overread = 0;
|
|
if (c->low >= 0xFF00) {
|
|
c->low = 0xFF00;
|
|
c->bytestream_end = c->bytestream;
|
|
}
|
|
}
|
|
|
|
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;
|
|
}
|