yading@10: /*
yading@10:  * MQ-coder decoder
yading@10:  * Copyright (c) 2007 Kamil Nowosad
yading@10:  *
yading@10:  * This file is part of FFmpeg.
yading@10:  *
yading@10:  * FFmpeg is free software; you can redistribute it and/or
yading@10:  * modify it under the terms of the GNU Lesser General Public
yading@10:  * License as published by the Free Software Foundation; either
yading@10:  * version 2.1 of the License, or (at your option) any later version.
yading@10:  *
yading@10:  * FFmpeg is distributed in the hope that it will be useful,
yading@10:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@10:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@10:  * Lesser General Public License for more details.
yading@10:  *
yading@10:  * You should have received a copy of the GNU Lesser General Public
yading@10:  * License along with FFmpeg; if not, write to the Free Software
yading@10:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@10:  */
yading@10: 
yading@10: /**
yading@10:  * MQ-coder decoder
yading@10:  * @file
yading@10:  * @author Kamil Nowosad
yading@10:  */
yading@10: 
yading@10: #include "mqc.h"
yading@10: 
yading@10: static void bytein(MqcState *mqc)
yading@10: {
yading@10:     if (*mqc->bp == 0xff){
yading@10:         if (*(mqc->bp+1) > 0x8f)
yading@10:             mqc->c++;
yading@10:         else{
yading@10:             mqc->bp++;
yading@10:             mqc->c += 2 + 0xfe00 - (*mqc->bp << 9);
yading@10:         }
yading@10:     } else{
yading@10:         mqc->bp++;
yading@10:         mqc->c += 1 + 0xff00 - (*mqc->bp << 8);
yading@10:     }
yading@10: }
yading@10: 
yading@10: static int exchange(MqcState *mqc, uint8_t *cxstate, int lps)
yading@10: {
yading@10:     int d;
yading@10:     if ((mqc->a < ff_mqc_qe[*cxstate]) ^ (!lps)){
yading@10:         if (lps)
yading@10:             mqc->a = ff_mqc_qe[*cxstate];
yading@10:         d = *cxstate & 1;
yading@10:         *cxstate = ff_mqc_nmps[*cxstate];
yading@10:     } else{
yading@10:         if (lps)
yading@10:             mqc->a = ff_mqc_qe[*cxstate];
yading@10:         d = 1 - (*cxstate & 1);
yading@10:         *cxstate = ff_mqc_nlps[*cxstate];
yading@10:     }
yading@10:     // renormd:
yading@10:     do{
yading@10:         if (!(mqc->c & 0xff)){
yading@10:             mqc->c -= 0x100;
yading@10:             bytein(mqc);
yading@10:         }
yading@10:         mqc->a += mqc->a;
yading@10:         mqc->c += mqc->c;
yading@10:     } while (!(mqc->a & 0x8000));
yading@10:     return d;
yading@10: }
yading@10: 
yading@10: void ff_mqc_initdec(MqcState *mqc, uint8_t *bp)
yading@10: {
yading@10:     ff_mqc_init_contexts(mqc);
yading@10:     mqc->bp = bp;
yading@10:     mqc->c = (*mqc->bp ^ 0xff) << 16;
yading@10:     bytein(mqc);
yading@10:     mqc->c = mqc->c << 7;
yading@10:     mqc->a = 0x8000;
yading@10: }
yading@10: 
yading@10: int ff_mqc_decode(MqcState *mqc, uint8_t *cxstate)
yading@10: {
yading@10:     mqc->a -= ff_mqc_qe[*cxstate];
yading@10:     if ((mqc->c >> 16) < mqc->a){
yading@10:         if (mqc->a & 0x8000)
yading@10:             return *cxstate & 1;
yading@10:         else
yading@10:             return exchange(mqc, cxstate, 0);
yading@10:     } else {
yading@10:         mqc->c -= mqc->a << 16;
yading@10:         return exchange(mqc, cxstate, 1);
yading@10:     }
yading@10: }