Configuring and Computing an FFT in C/C++

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 3/31/2023

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Configuring and Computing an FFT in C/C++

The table below summarizes information on configuring and computing an FFT in C/C++ for all kinds of transforms and possible combinations of input and output domains.

FFT to Compute	Input Data	Output Data	Required FFT Function Calls
Complex-to-complex, in-place, forward or backward	Interleaved complex numbers	Interleaved complex numbers	/* Configure a Descriptor / status = DftiCreateDescriptor(&hand, `<precision>`, DFTI_COMPLEX, `<dimension>`, `<sizes>`); status = DftiCommitDescriptor(hand); / Compute an FFT / / forward FFT / status = DftiComputeForward(hand, X_inout); / or backward FFT */ status = DftiComputeBackward(hand, X_inout);
Complex-to-complex, out-of-place, forward or backward	Interleaved complex numbers	Interleaved complex numbers	/* Configure a Descriptor / status = DftiCreateDescriptor(&hand, `<precision>`, DFTI_COMPLEX, `<dimension>`, `<sizes>`); status = DftiSetValue(hand, DFTI_PLACEMENT, DFTI_NOT_INPLACE); status = DftiCommitDescriptor(hand); / Compute an FFT / / forward FFT / status = DftiComputeForward(hand, X_in, Y_out); / or backward FFT */ status = DftiComputeBackward(hand, X_in, Y_out);
Complex-to-complex, in-place, forward or backward	Split-complex numbers	Split-complex numbers	/* Configure a Descriptor / status = DftiCreateDescriptor(&hand, `<precision>`, DFTI_COMPLEX, `<dimension>`, `<sizes>`); status = DftiSetValue(hand, DFTI_COMPLEX_STORAGE, DFTI_REAL_REAL); status = DftiCommitDescriptor(hand); / Compute an FFT / / forward FFT / status = DftiComputeForward(hand, Xre_inout, Xim_inout); / or backward FFT */ status = DftiComputeBackward(hand, Xre_inout, Xim_inout);
Complex-to-complex, out-of-place, forward or backward	Split-complex numbers	Split-complex numbers	/* Configure a Descriptor / status = DftiCreateDescriptor(&hand, `<precision>`, DFTI_COMPLEX, `<dimension>`, `<sizes>`); status = DftiSetValue(hand, DFTI_COMPLEX_STORAGE, DFTI_REAL_REAL); status = DftiSetValue(hand, DFTI_PLACEMENT, DFTI_NOT_INPLACE); status = DftiCommitDescriptor(hand); / Compute an FFT / / forward FFT / status = DftiComputeForward(hand, Xre_in, Xim_in, Yre_out, Yim_out); / or backward FFT */ status = DftiComputeBackward(hand, Xre_in, Xim_in, Yre_out, Yim_out);
Real-to-complex, in-place, forward	Real numbers	Numbers in the CCE format	/* Configure a Descriptor / status = DftiCreateDescriptor(&hand, `<precision>`, DFTI_REAL, `<dimension>`, `<sizes>`); status = DftiSetValue(hand, DFTI_CONJUGATE_EVEN_STORAGE, DFTI_COMPLEX_COMPLEX); status = DftiSetValue(hand, DFTI_PACKED_FORMAT, DFTI_CCE_FORMAT); status = DftiSetValue(hand, DFTI_INPUT_STRIDES, `<real_strides>`); status = DftiSetValue(hand, DFTI_OUTPUT_STRIDES, `<complex_strides>`); status = DftiCommitDescriptor(hand); / Compute an FFT */ status = DftiComputeForward(hand, X_inout);
Real-to-complex, out-of-place, forward	Real numbers	Numbers in the CCE format	/* Configure a Descriptor / status = DftiCreateDescriptor(&hand, `<precision>`, DFTI_REAL, `<dimension>`, `<sizes>`); status = DftiSetValue(hand, DFTI_CONJUGATE_EVEN_STORAGE, DFTI_COMPLEX_COMPLEX); status = DftiSetValue(hand, DFTI_PACKED_FORMAT, DFTI_CCE_FORMAT); status = DftiSetValue(hand, DFTI_PLACEMENT, DFTI_NOT_INPLACE); status = DftiSetValue(hand, DFTI_INPUT_STRIDES, `<real_strides>`); status = DftiSetValue(hand, DFTI_OUTPUT_STRIDES, `<complex_strides>`); status = DftiCommitDescriptor(hand); / Compute an FFT */ status = DftiComputeForward(hand, X_in, Y_out);
Complex-to-real, in-place, backward	Numbers in the CCE format	Real numbers	/* Configure a Descriptor / status = DftiCreateDescriptor(&hand, `<precision>`, DFTI_REAL, `<dimension>`, `<sizes>`); status = DftiSetValue(hand, DFTI_CONJUGATE_EVEN_STORAGE, DFTI_COMPLEX_COMPLEX); status = DftiSetValue(hand, DFTI_PACKED_FORMAT, DFTI_CCE_FORMAT); status = DftiSetValue(hand, DFTI_INPUT_STRIDES, `<complex_strides>`); status = DftiSetValue(hand, DFTI_OUTPUT_STRIDES, `<real_strides>`); status = DftiCommitDescriptor(hand); / Compute an FFT */ status = DftiComputeBackward(hand, X_inout);
Complex-to-real, out-of-place, backward	Numbers in the CCE format	Real numbers	/* Configure a Descriptor / status = DftiCreateDescriptor(&hand, `<precision>`, DFTI_REAL, `<dimension>`, `<sizes>`); status = DftiSetValue(hand, DFTI_CONJUGATE_EVEN_STORAGE, DFTI_COMPLEX_COMPLEX); status = DftiSetValue(hand, DFTI_PLACEMENT, DFTI_NOT_INPLACE); status = DftiSetValue(hand, DFTI_PACKED_FORMAT, DFTI_CCE_FORMAT); status = DftiSetValue(hand, DFTI_INPUT_STRIDES, `<complex_strides>`); status = DftiSetValue(hand, DFTI_OUTPUT_STRIDES, `<real_strides>`); status = DftiCommitDescriptor(hand); / Compute an FFT */ status = DftiComputeBackward(hand, X_in, Y_out);

You can find C programs that illustrate configuring and computing FFTs in the examples/dftc/ subdirectory of your Intel® oneAPI Math Kernel Library directory.

Parent topic: FFT Computation Functions

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Developer Reference for Intel® oneAPI Math Kernel Library for C

Configuring and Computing an FFT in C/C++