static int DecodeACSign(WinZipJPEGDecompressor *self,int comp,unsigned int k,int absvalue,
const WinZipJPEGBlock *current,const WinZipJPEGBlock *north,const WinZipJPEGBlock *west,
const WinZipJPEGQuantizationTable *quantization)
{
// Decode sign. (5.6.6.4)
// Calculate sign context, or decode with fixed probability. (5.6.6.4.1)
int predictedsign;
if(IsFirstRowOrColumn(k))
{
int bdr=BDR(k,current,north,west,quantization);
if(bdr==0) return NextBitFromWinZipJPEGArithmeticDecoder(&self->decoder,&self->fixedcontext);
predictedsign=(bdr<0);
}
else if(k==4)
{
int sign1=Sign(north->c[k]);
int sign2=Sign(west->c[k]);
if(sign1+sign2==0) return NextBitFromWinZipJPEGArithmeticDecoder(&self->decoder,&self->fixedcontext);
predictedsign=(sign1+sign2<0);
}
else if(IsSecondRow(k))
{
if(north->c[k]==0) return NextBitFromWinZipJPEGArithmeticDecoder(&self->decoder,&self->fixedcontext);
predictedsign=(north->c[k]<0);
}
else if(IsSecondColumn(k))
{
if(west->c[k]==0) return NextBitFromWinZipJPEGArithmeticDecoder(&self->decoder,&self->fixedcontext);
predictedsign=(west->c[k]<0);
}
else
{
return NextBitFromWinZipJPEGArithmeticDecoder(&self->decoder,&self->fixedcontext);
}
static const int n_for_k[64]={
0,
0, 1,
2, 3, 4,
5, 6, 7, 8,
9,10, 0,11,12,
13,14, 0, 0,15,16,
17,18, 0, 0, 0,19,20,
21,22, 0, 0, 0, 0,23,24,
25, 0, 0, 0, 0, 0,26,
0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0,
0, 0, 0, 0,
0, 0, 0,
0, 0,
0,
};
int n=n_for_k[k];
int signcontext1=Min(Category(absvalue)/2,2);
return NextBitFromWinZipJPEGArithmeticDecoder(&self->decoder,
&self->acsignbins[comp][n][signcontext1][predictedsign]);
}
static void CompressACSign(JPEGCompressor *self,int comp,unsigned int k,int absvalue,
const JPEGBlock *current,const JPEGBlock *north,const JPEGBlock *west,
const JPEGQuantizationTable *quantization)
{
int sign=current->c[k]<0;
// Calculate sign context, or compress with fixed probability.
int predictedsign;
if(IsFirstRowOrColumn(k))
{
int bdr=BDR(k,current,north,west,quantization);
if(bdr==0)
{
WriteBit(&self->encoder,sign,0x800);
return;
}
predictedsign=(bdr<0);
}
else if(k==4)
{
int sign1=Sign(north->c[k]);
int sign2=Sign(west->c[k]);
if(sign1+sign2==0)
{
WriteBit(&self->encoder,sign,0x800);
return;
}
predictedsign=(sign1+sign2<0);
}
else if(IsSecondRow(k))
{
if(north->c[k]==0)
{
WriteBit(&self->encoder,sign,0x800);
return;
}
predictedsign=(north->c[k]<0);
}
else if(IsSecondColumn(k))
{
if(west->c[k]==0)
{
WriteBit(&self->encoder,sign,0x800);
return;
}
predictedsign=(west->c[k]<0);
}
else
{
WriteBit(&self->encoder,sign,0x800);
return;
}
static const int n_for_k[64]={
0,
0, 1,
2, 3, 4,
5, 6, 7, 8,
9,10, 0,11,12,
13,14, 0, 0,15,16,
17,18, 0, 0, 0,19,20,
21,22, 0, 0, 0, 0,23,24,
25, 0, 0, 0, 0, 0,26,
0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0,
0, 0, 0, 0,
0, 0, 0,
0, 0,
0,
};
int n=n_for_k[k];
int signcontext1=Min(Category(absvalue)/2,2);
WriteDynamicBit(&self->encoder,sign,
&self->acsignbins[comp][n][signcontext1][predictedsign],
self->acsignshift);
}
