Intel® oneAPI Math Kernel Library Developer Reference - C
If you need to perform a large number of identical FFTs, you can do this in a single call to a DftiCompute* function with the value of the DFTI_NUMBER_OF_TRANSFORMS configuration parameter equal to the actual number of the transforms. The default value of this parameter is one. You can set this parameter to a positive integer value using the MKL_LONG data type. When setting the number of transforms to a value greater than one, you also need to specify the distance between the input data sets and the distance between the output data sets using one of the DFTI_INPUT_DISTANCE and DFTI_OUTPUT_DISTANCE configuration parameters or both.
The data sets to be transformed must not have common elements.
All the sets of data must be located within the same memory block.
To better understand the use of the DFTI_NUMBER_OF_TRANSFORMSconfiguration parameter, see this example in your Intel® oneAPI Math Kernel Library directory:
./examples/dftc/source/config_number_of_transforms.c