Developer Reference

Contents

DFTI_ORDERING

Some FFT algorithms apply an explicit permutation stage that is time consuming [4]. The exclusion of this step is similar to applying an FFT to input data whose order is scrambled, or allowing a scrambled order of the FFT results. In applications such as convolution and power spectrum calculation, the order of result or data is unimportant and thus using scrambled data is acceptable if it leads to better performance. The following options are available in
Intel® MKL
:
  • DFTI_ORDERED
    : Forward transform data ordered, backward transform data ordered (default option).
  • DFTI_BACKWARD_SCRAMBLED
    : Forward transform data ordered, backward transform data scrambled.
Table
"Scrambled Order Transform"
tabulates the effect of this configuration setting.
Scrambled Order Transform
DftiComputeForward
DftiComputeBackward
DFTI_ORDERING
Input → Output
Input → Output
DFTI_ORDERED
ordered → ordered
ordered → ordered
DFTI_BACKWARD_SCRAMBLED
ordered → scrambled
scrambled → ordered
The word "scrambled" in this table means "permit scrambled order if possible". In some situations permitting out-of-order data gives no performance advantage and an implementation may choose to ignore the suggestion.

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.

Notice revision #20110804