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/*
* MQ-coder decoder
* Copyright (c) 2007 Kamil Nowosad
*
* 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
*/
/**
* MQ-coder decoder
* @file
* @author Kamil Nowosad
*/
#include "mqc.h"
static void bytein(MqcState *mqc)
{
if (*mqc->bp == 0xff) {
if (*(mqc->bp + 1) > 0x8f)
mqc->c++;
else {
mqc->bp++;
mqc->c += 2 + 0xfe00 - (*mqc->bp << 9);
}
} else {
mqc->bp++;
mqc->c += 1 + 0xff00 - (*mqc->bp << 8);
}
}
static int exchange(MqcState *mqc, uint8_t *cxstate, int lps)
{
int d;
if ((mqc->a < ff_mqc_qe[*cxstate]) ^ (!lps)) {
if (lps)
mqc->a = ff_mqc_qe[*cxstate];
d = *cxstate & 1;
*cxstate = ff_mqc_nmps[*cxstate];
} else {
if (lps)
mqc->a = ff_mqc_qe[*cxstate];
d = 1 - (*cxstate & 1);
*cxstate = ff_mqc_nlps[*cxstate];
}
// do RENORMD: see ISO/IEC 15444-1:2002 §C.3.3
do {
if (!(mqc->c & 0xff)) {
mqc->c -= 0x100;
bytein(mqc);
}
mqc->a += mqc->a;
mqc->c += mqc->c;
} while (!(mqc->a & 0x8000));
return d;
}
void ff_mqc_initdec(MqcState *mqc, uint8_t *bp)
{
ff_mqc_init_contexts(mqc);
mqc->bp = bp;
mqc->c = (*mqc->bp ^ 0xff) << 16;
bytein(mqc);
mqc->c = mqc->c << 7;
mqc->a = 0x8000;
}
int ff_mqc_decode(MqcState *mqc, uint8_t *cxstate)
{
mqc->a -= ff_mqc_qe[*cxstate];
if ((mqc->c >> 16) < mqc->a) {
if (mqc->a & 0x8000)
return *cxstate & 1;
else
return exchange(mqc, cxstate, 0);
} else {
mqc->c -= mqc->a << 16;
return exchange(mqc, cxstate, 1);
}
}
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