I am currently debugging my code, where I use the CUDA FFT routines.
I have something like this (please see comments for my thoughts on what I do):
#include <cufft.h>
#include <cuda.h>
#include <cuda_runtime.h>
#include <cuComplex.h>
void foo(double* real, double* imag, size_t size)
{
cufftHandle plan;
cufftDoubleComplex* inputData;
cufftDoubleReal* outputReal;
//Allocation of arrays:
size_t allocSizeInput = sizeof(cufftDoubleComplex) * size;
size_t allocSizeOutput = sizeof(cufftDoubleReal) * (size - 1) * 2;
cudaMalloc((void**)&outputReal, allocSizeOutput);
cudaMalloc((void**)&inputData, allocSizeInput);
//Now I put the data in the arrays real and imag into input data by
//interleaving it
cudaMemcpy2D(static_cast<void*>(inputData),
2 * sizeof (double),
static_cast<const void*>(real),
sizeof(double),
sizeof(double),
size,
cudaMemcpyHostToDevice);
cudaMemcpy2D(static_cast<void*>(inputData) + sizeof(double),
2 * sizeof (double),
static_cast<const void*>(imag),
sizeof(double),
sizeof(double),
size,
cudaMemcpyHostToDevice);
//I checked inputData at this point and it does indeed look like i expect it to.
//Now I create the plan
cufftPlan1d(&plan, size, CUFFT_Z2D, 1);
//Now I execute the plan
cufftExecZ2D(plan, inputData, outputReal);
//Now I wait for device sync
cudaDeviceSynchronize();
//Now I fetch up the data from device
double* outDbl = new double[(size-1)*2]
cudaMemcpy(static_cast<void*>(outDbl),
static_cast<void*>(outputReal),
allocSizeOutput,
cudaMemcpyDeviceToHost);
//Here I am doing other fancy stuff which is not important
}
So the problem I have now is, that the results in outDbl are not what I expect them to be. For example, if I give the following values into this function:
real = [0 -5.567702511594111 -5.595068807897317 -5.595068807897317 -5.567702511594111]
imag = [0 9.678604224870535 2.280007038673738 -2.280007038673738 -9.678604224870535]
I expect to get:
result = [-4.46511 -3.09563 -0.29805 2.51837 5.34042]
But i get something completely different.
What do I do wrong? Did I misunderstand the FFT function? Is it not basically the inverse FFT from complex to real? Is there a problem in my data copy routines?
I must admit I am a bit lost on this one.
