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