Developer Reference for Intel® oneAPI Math Kernel Library - C

Developer Reference

  • 0.9
  • 09/09/2020
  • Public Content
Contents

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.

Product and Performance Information

1

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

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