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107 lines
2.5 KiB
C
107 lines
2.5 KiB
C
/*
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* RangeCoder.c
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*
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* Copyright (c) 2017-present, MacPaw Inc. All rights reserved.
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*
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* This library 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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* This library 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 this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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* MA 02110-1301 USA
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*/
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#include "RangeCoder.h"
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void InitializePPMdRangeCoder(PPMdRangeCoder *self,
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PPMdReadFunction *readfunc,void *inputcontext,
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bool uselow,int bottom)
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{
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self->readfunc=readfunc;
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self->inputcontext=inputcontext;
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self->low=0;
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self->code=0;
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self->range=0xffffffff;
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self->uselow=uselow;
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self->bottom=bottom;
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for(int i=0;i<4;i++) self->code=(self->code<<8)|readfunc(inputcontext);
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}
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uint32_t PPMdRangeCoderCurrentCount(PPMdRangeCoder *self,uint32_t scale)
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{
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self->range/=scale;
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return (self->code-self->low)/self->range;
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}
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void RemovePPMdRangeCoderSubRange(PPMdRangeCoder *self,uint32_t lowcount,uint32_t highcount)
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{
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if(self->uselow) self->low+=self->range*lowcount;
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else self->code-=self->range*lowcount;
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self->range*=highcount-lowcount;
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NormalizePPMdRangeCoder(self);
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}
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int NextWeightedBitFromPPMdRangeCoder(PPMdRangeCoder *self,int weight,int size)
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{
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uint32_t val=PPMdRangeCoderCurrentCount(self,size);
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if(val<weight)
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{
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RemovePPMdRangeCoderSubRange(self,0,weight);
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return 0;
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}
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else
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{
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RemovePPMdRangeCoderSubRange(self,weight,size);
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return 1;
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}
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}
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int NextWeightedBitFromPPMdRangeCoder2(PPMdRangeCoder *self,int weight,int shift)
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{
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uint32_t threshold=(self->range>>shift)*weight;
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int bit;
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if(self->code<threshold) // <= ?
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{
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bit=0;
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self->range=threshold;
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}
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else
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{
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bit=1;
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self->range-=threshold;
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self->code-=threshold;
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}
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NormalizePPMdRangeCoder(self);
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return bit;
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}
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void NormalizePPMdRangeCoder(PPMdRangeCoder *self)
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{
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for(;;)
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{
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if( (self->low^(self->low+self->range))>=0x1000000 )
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{
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if(self->range>=self->bottom) break;
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else self->range=-self->low&(self->bottom-1);
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}
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int byte=self->readfunc(self->inputcontext);
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self->code=(self->code<<8)|byte;
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self->range<<=8;
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self->low<<=8;
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}
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}
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