static int DecodeACComponent(WinZipJPEGDecompressor *self,int comp,unsigned int k,bool canbezero,
const WinZipJPEGBlock *current,const WinZipJPEGBlock *north,const WinZipJPEGBlock *west,
const WinZipJPEGQuantizationTable *quantization)
{
if(!north) north=&ZeroBlock;
if(!west) west=&ZeroBlock;
int val1;
if(IsFirstRowOrColumn(k)) val1=Abs(BDR(k,current,north,west,quantization));
else val1=Average(k,north,west,quantization);
int val2=Sum(k,current);
if(canbezero)
{
// Decode zero/non-zero bit. (5.6.6.1)
int zerocontext1=Min(Category(val1),2);
int zerocontext2=Min(Category(val2),5);
int nonzero=NextBitFromWinZipJPEGArithmeticDecoder(&self->decoder,
&self->zerobins[comp][k-1][zerocontext1][zerocontext2]);
// If this component is zero, there is no need to decode further parameters.
if(!nonzero) return 0;
}
// This component is not zero. Proceed with decoding absolute value.
int absvalue;
// Decode pivot (abs>=2). (5.6.6.2)
int pivotcontext1=Min(Category(val1),4);
int pivotcontext2=Min(Category(val2),6);
int pivot=NextBitFromWinZipJPEGArithmeticDecoder(&self->decoder,
&self->pivotbins[comp][k-1][pivotcontext1][pivotcontext2]);
if(!pivot)
{
// The absolute of this component is not >=2. It must therefore be 1,
// and there is no need to decode the value.
absvalue=1;
}
else
{
// The absolute of this component is >=2. Proceed with decoding
// the absolute value. (5.6.6.3)
int val3,n;
if(IsFirstRow(k)) { val3=Column(k)-1; n=0; }
else if(IsFirstColumn(k)) { val3=Row(k)-1; n=1; }
else { val3=Category(k-4); n=2; }
int magnitudecontext1=Min(Category(val1),8);
int magnitudecontext2=Min(Category(val2),8);
int remaindercontext=val3;
// Decode absolute value.
absvalue=DecodeBinarization(&self->decoder,
self->acmagnitudebins[comp][n][magnitudecontext1][magnitudecontext2],
self->acremainderbins[comp][n][remaindercontext],
14,9)+2;
}
if(DecodeACSign(self,comp,k,absvalue,current,north,west,quantization)) return -absvalue;
else return absvalue;
}
static bool IsFirstRowOrColumn(unsigned int k) { return IsFirstRow(k)||IsFirstColumn(k); }
static void CompressACComponent(JPEGCompressor *self,int comp,unsigned int k,bool canbezero,
const JPEGBlock *current,const JPEGBlock *north,const JPEGBlock *west,
const JPEGQuantizationTable *quantization)
{
int value=current->c[k];
if(!north) north=&ZeroBlock;
if(!west) west=&ZeroBlock;
int val1;
if(IsFirstRowOrColumn(k)) val1=Abs(BDR(k,current,north,west,quantization));
else val1=Average(k,north,west,quantization);
int val2=Sum(k,current);
if(canbezero)
{
// Compress zero/non-zero bit.
int zerocontext1=Min(Category(val1),2);
int zerocontext2=Min(Category(val2),5);
WriteDynamicBit(&self->encoder,value!=0,
&self->zerobins[comp][k-1][zerocontext1][zerocontext2],
self->zeroshift);
// If this component is zero, there is no need to compress further parameters.
if(value==0) return;
}
// This component is not zero. Proceed with compressing absolute value.
int absvalue=Abs(value);
// Compress pivot (abs>=2).
int pivotcontext1=Min(Category(val1),4);
int pivotcontext2=Min(Category(val2),6);
WriteDynamicBit(&self->encoder,absvalue>1,
&self->pivotbins[comp][k-1][pivotcontext1][pivotcontext2],
self->pivotshift);
if(absvalue>1)
{
// The absolute of this component is >=2. Proceed with compressing
// the absolute value.
int val3,n;
if(IsFirstRow(k)) { val3=Column(k)-1; n=0; }
else if(IsFirstColumn(k)) { val3=Row(k)-1; n=1; }
else { val3=Category(k-4); n=2; }
int magnitudecontext1=Min(Category(val1),8);
int magnitudecontext2=Min(Category(val2),8);
int remaindercontext=val3;
// Compress absolute value.
WriteUniversalCode(&self->encoder,absvalue-2,
self->acmagnitudebins[comp][n][magnitudecontext1][magnitudecontext2],
self->acmagnitudeshift,
self->acremainderbins[comp][n][remaindercontext],
self->acremaindershift);
}
CompressACSign(self,comp,k,absvalue,current,north,west,quantization);
}