/*
  * 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];
     }
     // renormd:
     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);
     }
 }