initialize large constant array as lookup table

I need a lookup table as multiplier.

so I create an array and filled with integer multiply.

and I try to implement like this. however, this takes very very long time to compile,

so I thought this may be wrong to achieve what I want to implement ? Is that because 256*256 is too large ?

Is there any better way to have same effect?

__Kernel myKernel(__global int b,__global int c,__global int idx){

int lut[256][256];

for(int i=-128;i<128;i++){

for(int j=-128;j<128;j++){

conv[i+128][j+128] = i*j;

}

}

int a=0;# pragma unroll 512

for(int i=0;i<idxd;i++){

// int a+=b*c;

int a+=lut[b+128][c+128];

}

}

---------------------------------------------

So I try to implement like this, however, compiler keeps telling me "constant data must be initialized."

maybe it's because constant array can't initialize by for-loop, is there any way to initialize this instead of filling 256*256 data?

constant int lut[256][256];

for(int i=-128;i<128;i++){

for(int j=-128;j<128;j++){

conv[i+128][j+128] = i*j;

}

}

__Kernel myKernel(__global int b,__global int c,__global int idx){

int a=0;# pragma unroll 512

for(int i=0;i<idxd;i++){

// int a+=b*c;

int a+=lut[b+128][c+128];

}

}