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/*
* Range coder
* Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
*
* This file is part of Libav.
*
* Libav 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.
*
* Libav 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 Libav; 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 "avcodec.h"
#include "rangecoder.h"
#include "bytestream.h"
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;
}
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 = bytestream_get_be16(&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);
assert(c->low == 0);
assert(c->range >= 0x100);
return c->bytestream - c->bytestream_start;
}
#ifdef TEST
#define SIZE 10240
#include "libavutil/lfg.h"
int main(void)
{
RangeCoder c;
uint8_t b[9 * SIZE];
uint8_t r[9 * SIZE];
int i;
uint8_t state[10];
AVLFG prng;
av_lfg_init(&prng, 1);
ff_init_range_encoder(&c, b, SIZE);
ff_build_rac_states(&c, 0.05 * (1LL << 32), 128 + 64 + 32 + 16);
memset(state, 128, sizeof(state));
for (i = 0; i < SIZE; i++)
r[i] = av_lfg_get(&prng) % 7;
for (i = 0; i < SIZE; i++) {
START_TIMER
put_rac(&c, state, r[i] & 1);
STOP_TIMER("put_rac")
}
ff_rac_terminate(&c);
ff_init_range_decoder(&c, b, SIZE);
memset(state, 128, sizeof(state));
for (i = 0; i < SIZE; i++) {
START_TIMER
if ((r[i] & 1) != get_rac(&c, state))
av_log(NULL, AV_LOG_DEBUG, "rac failure at %d\n", i);
STOP_TIMER("get_rac")
}
return 0;
}
#endif /* TEST */
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