what is the corresponding function of DFT in IPP?

missing__zlw · ‎10-11-2010

Hi,

I am trying to comparing using MKL's DFT and IPP's DFT.

However, my test program gives different results:

In MKL:

MKL_LONG status = DftiCreateDescriptor( &my_desc1_handled, DFTI_SINGLE, DFTI_COMPLEX, 2, l);

status = DftiSetValue( my_desc1_handled, DFTI_PLACEMENT, DFTI_NOT_INPLACE);

status = DftiCommitDescriptor( my_desc1_handled);

status = DftiComputeForward( my_desc1_handled, A, B0 );

status = DftiFreeDescriptor(&my_desc1_handled);

In IPP:

IppsDFTSpec_C_32fc *pDFTSpec;

ippsDFTInitAlloc_C_32fc( &pDFTSpec, len, IPP_FFT_DIV_INV_BY_N,

ippAlgHintAccurate );

ippsDFTFwd_CToC_32fc(pSrc, (Ipp32fc*)pDst, pDFTSpec, 0 );

ippsDFTFree_C_32fc(pDFTSpec);

I am looking forward to complex to complex transform with matrix M*N dimension.

Two question:

1. what settings did I use wrong as my IPP give different result compared to MKL.

2. How do I specify the 2 D dimension in IPP? Here "len" inippsDFTInitAlloc_C_32fc is a 1d number which I used M*N value.

Thanks.

Evgueni_P_Intel · ‎10-12-2010

Hi zlw,

Intel IPP libraries do only single precision 2D FFTs. Here's a simple example that is supposed to do complex FFT(5x10). Please consult the documentation for the Intel IPP Image Processing library for more information.

[cpp]#include "ipp.h"
#include 

int main()
{
    float _Complex x[5][10], y[5][10];
    IppiSize len = {5, 10};
    IppiDFTSpec_C_32fc *fft = NULL;
    IppStatus status = ippStsNoErr;
    status = ippiDFTInitAlloc_C_32fc(&fft, len, IPP_FFT_NODIV_BY_ANY, ippAlgHintAccurate); // expect ippStsNoErr
    status = ippiDFTFwd_CToC_32fc_C1R(x, 10, y, 10, fft, NULL); // expect ippStsNoErr
    status = ippiDFTFree_C_32fc(fft); // expect ippStsNoErr
    return 0;
}
[/cpp]