Intel® oneAPI Math Kernel Library (oneMKL) - Data Parallel C++ Developer Reference

Developer Reference

Contents

descriptor<precision, domain>::set_value

Sets one configuration parameter with the specified configuration value. This routine belongs to the
oneapi::mkl::dft
 namespace.

Description

This function sets one configuration parameter with the specified configuration value and throws an
std::runtime_exception
 in the case that it fails. Each configuration parameter is a named constant, and the configuration value must have the corresponding type, which can be a named constant or a native type. The DPC++ configuration parameters have type
mkl::dft::config_param
. Each parameter
mkl::dft::config_param::<PARAMETER_NAME>
 has the same meaning and possible values as the C interface’s
DFTI_<PARAMETER_NAME>
. Some of the options available in the C interface are not fully supported in the DPC++ interface yet. See the note below and the Intel® oneAPI Math Kernel Library Release Notes. For a full description of each parameter’s meaning and options, see Config Params.
  • An important difference in the configuration options for DPC++ FFT interface is the use of
    FWD_DISTANCE
     and
    BWD_DISTANCE
     instead of
    INPUT_DISTANCE
     and
    OUTPUT_DISTANCE
    . The
    FWD_DISTANCE
     describes the number of elements between different batched FFTs for the forward domain while
    BWD_DISTANCE
     describes the number of elements between different batched FFTs for the backward domain. This allows a committed descriptor to compute both forward and backward transforms without resetting the distance parameters. It is required for all R2C or C2R transforms to use
    FWD_DISTANCE
     and
    BWD_DISTANCE
     instead of
    INPUT_DISTANCE
     and
    OUTPUT_DISTANCE
    .
  • For
    COMPLEX_STORAGE
    , only the
    DFTI_COMPLEX_COMPLEX
     format is currently supported on CPU and GPU devices. Both
    DFTI_COMPLEX_COMPLEX
     and
    DFTI_REAL_REAL
     are supported on the host device.
  • In the case of a real forward domain, the only supported values on GPU devices for
    CONJUGATE_EVEN_STORAGE
     and
    PACKED_FORMAT
     are respectively
    DFTI_COMPLEX_COMPLEX
     and
    DFTI_CCE_FORMAT
    . These values are set by default and require the setting of the
    INPUT_STRIDE
     and
    OUTPUT_STRIDE
     parameters before calling commit. (While these default values differ from the current C interface defaults, the C default values will be brought into alignment with these default values following the full deprecation process of the current C default values. See the deprecation notice at DFTI_COMPLEX_STORAGE, DFTI_REAL_STORAGE, DFTI_CONJUGATE_EVEN_STORAGE.)
  • In the case of a real forward domain, arbitrary strides and batch distances are not supported for multi-dimensional transforms on GPU. Considering the last dimension of the data, every element must be separated from its nearest peer(s) (along another dimension and/or in another batch) by a constant distance. For example, to compute a batched, two-dimensional R2C FFT of size
    [N2, N1]
     with input strides
    [0, S2, 1]
     (row-major layout with unit elementary stride and no offset),
    FWD_DISTANCE
     must be equal to
    N2*S2
     so that every element is separated from its nearest last-dimension counterpart(s) by a distance
    S2
     (in this example), even across batches.
The set_value function cannot be used to change configuration parameters
mkl::dft::config_param::FORWARD_DOMAIN
,
mkl::dft::config_param::PRECISION
 since these are a part of the template. Likewise,
mkl::dft::config_param::LENGTHS
 is set with the constructor.
All calls to
set_value()
 must be done before calls to
commit()
. This is because the handle may have been moved to an offloaded device after
commit()
.
Function calls needed to configure an FFT descriptor for a particular call to an FFT computation function are summarized in Configuring and Computing an FFT in C/C++.

API

Syntax
namespace oneapi::mkl::dft{
  void descriptor<prec,dom>::set_value(config_param param, ...);
}
Include Files
  • oneapi/mkl/dfti.hpp
Input Parameters
Name
Type
Description
param
mkl::dft::config_param
Configuration parameter
value
Depends on the configuration parameter
Configuration value

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.