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#import "CarrylessRangeCoder.h"
void InitializeRangeCoder(CarrylessRangeCoder *self,CSInputBuffer *input,BOOL uselow,int bottom)
{
self->input=input;
self->low=0;
self->code=0;
self->range=0xffffffff;
self->uselow=uselow;
self->bottom=bottom;
self->code=CSInputNextUInt32BE(input);
//for(int i=0;i<4;i++) self->code=(self->code<<8)|CSInputNextByte(input);
}
uint32_t RangeCoderCurrentCount(CarrylessRangeCoder *self,uint32_t scale)
{
self->range/=scale;
return (self->code-self->low)/self->range;
}
void RemoveRangeCoderSubRange(CarrylessRangeCoder *self,uint32_t lowcount,uint32_t highcount)
{
if(self->uselow) self->low+=self->range*lowcount;
else self->code-=self->range*lowcount;
self->range*=highcount-lowcount;
NormalizeRangeCoder(self);
}
int NextSymbolFromRangeCoder(CarrylessRangeCoder *self,uint32_t *freqtable,int numfreq)
{
uint32_t totalfreq=0;
for(int i=0;i<numfreq;i++) totalfreq+=freqtable[i];
uint32_t tmp=RangeCoderCurrentCount(self,totalfreq);
uint32_t cumulativefreq=0;
uint32_t n=0;
while(n<numfreq-1&&cumulativefreq+freqtable[n]<=tmp) cumulativefreq+=freqtable[n++];
RemoveRangeCoderSubRange(self,cumulativefreq,cumulativefreq+freqtable[n]);
return n;
}
int NextBitFromRangeCoder(CarrylessRangeCoder *self)
{
int bit=RangeCoderCurrentCount(self,2);
if(bit==0) RemoveRangeCoderSubRange(self,0,1);
else RemoveRangeCoderSubRange(self,1,2);
return bit;
}
int NextWeightedBitFromRangeCoder(CarrylessRangeCoder *self,int weight,int size)
{
uint32_t val=RangeCoderCurrentCount(self,size);
int bit;
if(val<weight) // <= ?
{
bit=0;
RemoveRangeCoderSubRange(self,0,weight);
}
else
{
bit=1;
RemoveRangeCoderSubRange(self,weight,size);
}
return bit;
}
int NextWeightedBitFromRangeCoder2(CarrylessRangeCoder *self,int weight,int shift)
{
uint32_t threshold=(self->range>>shift)*weight;
int bit;
if(self->code<threshold) // <= ?
{
bit=0;
self->range=threshold;
}
else
{
bit=1;
self->range-=threshold;
self->code-=threshold;
}
NormalizeRangeCoder(self);
return bit;
}
void NormalizeRangeCoder(CarrylessRangeCoder *self)
{
for(;;)
{
if( (self->low^(self->low+self->range))>=0x1000000 )
{
if(self->range>=self->bottom) break;
else self->range=-self->low&(self->bottom-1);
}
self->code=(self->code<<8) | CSInputNextByte(self->input);
self->range<<=8;
self->low<<=8;
}
}
/*int NextSymbolFromRangeCoderCumulative(CarrylessRangeCoder *self,uint32_t *cumulativetable,int stride)
{
uint32_t totalfreq=*cumulativetable;
cumulativetable=(uint32_t *)((uint8_t *)cumulativetable+stride);
self->range/=totalfreq;
uint32_t tmp=(self->code-self->low)/self->range;
uint32_t n=0,curr;
do
{
curr=*cumulativetable;
cumulativetable=(uint32_t *)((uint8_t *)cumulativetable+stride);
n++;
} while(tmp<curr);
cumulativetable=(uint32_t *)((uint8_t *)cumulativetable-2*stride);
uint32_t prev=*cumulativetable;
self->low+=self->range*curr;
self->range*=prev-curr;
NormalizeRangeCoder(self);
return n-1;
}*/
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