// Extract real parts, copy them from src to dst.
// In the meanwhile, check if imaginary parts are nearly zero
// and scale the kernel to compensate for unnormalized FFTs.
func scaleRealParts(dst, src *data.Slice, scale float32) {
util.Argument(2*dst.Len() == src.Len())
util.Argument(dst.NComp() == 1 && src.NComp() == 1)
srcList := src.HostCopy().Host()[0]
dstList := dst.Host()[0]
// Normally, the FFT'ed kernel is purely real because of symmetry,
// so we only store the real parts...
maximg := float32(0.)
maxreal := float32(0.)
for i := 0; i < src.Len()/2; i++ {
dstList[i] = srcList[2*i] * scale
if fabs(srcList[2*i+0]) > maxreal {
maxreal = fabs(srcList[2*i+0])
}
if fabs(srcList[2*i+1]) > maximg {
maximg = fabs(srcList[2*i+1])
}
}
// ...however, we check that the imaginary parts are nearly zero,
// just to be sure we did not make a mistake during kernel creation.
if maximg/maxreal > FFT_IMAG_TOLERANCE {
log.Fatalf("Too large FFT kernel imaginary/real part: %v", maximg/maxreal)
}
}