mirror of
https://github.com/FFmpeg/FFmpeg.git
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122 lines
3.4 KiB
C
122 lines
3.4 KiB
C
/*
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* Range coder
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* Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file
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* Range coder.
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* based upon
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* "Range encoding: an algorithm for removing redundancy from a digitised
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* message.
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* G. N. N. Martin Presented in March 1979 to the Video &
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* Data Recording Conference,
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* IBM UK Scientific Center held in Southampton July 24-27 1979."
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*/
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#include <string.h>
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#include "libavutil/attributes.h"
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#include "libavutil/avassert.h"
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#include "libavutil/intreadwrite.h"
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#include "avcodec.h"
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#include "rangecoder.h"
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av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
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{
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c->bytestream_start =
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c->bytestream = buf;
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c->bytestream_end = buf + buf_size;
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c->low = 0;
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c->range = 0xFF00;
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c->outstanding_count = 0;
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c->outstanding_byte = -1;
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}
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av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf,
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int buf_size)
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{
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/* cast to avoid compiler warning */
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ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
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c->low = AV_RB16(c->bytestream);
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c->bytestream += 2;
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c->overread = 0;
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if (c->low >= 0xFF00) {
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c->low = 0xFF00;
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c->bytestream_end = c->bytestream;
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}
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}
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void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
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{
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const int64_t one = 1LL << 32;
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int64_t p;
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int last_p8, p8, i;
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memset(c->zero_state, 0, sizeof(c->zero_state));
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memset(c->one_state, 0, sizeof(c->one_state));
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last_p8 = 0;
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p = one / 2;
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for (i = 0; i < 128; i++) {
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p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
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if (p8 <= last_p8)
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p8 = last_p8 + 1;
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if (last_p8 && last_p8 < 256 && p8 <= max_p)
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c->one_state[last_p8] = p8;
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p += ((one - p) * factor + one / 2) >> 32;
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last_p8 = p8;
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}
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for (i = 256 - max_p; i <= max_p; i++) {
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if (c->one_state[i])
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continue;
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p = (i * one + 128) >> 8;
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p += ((one - p) * factor + one / 2) >> 32;
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p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
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if (p8 <= i)
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p8 = i + 1;
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if (p8 > max_p)
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p8 = max_p;
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c->one_state[i] = p8;
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}
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for (i = 1; i < 255; i++)
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c->zero_state[i] = 256 - c->one_state[256 - i];
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}
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/* Return the number of bytes written. */
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int ff_rac_terminate(RangeCoder *c)
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{
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c->range = 0xFF;
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c->low += 0xFF;
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renorm_encoder(c);
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c->range = 0xFF;
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renorm_encoder(c);
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av_assert1(c->low == 0);
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av_assert1(c->range >= 0x100);
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return c->bytestream - c->bytestream_start;
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}
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