Flags are used to tune the library during the setup time to use the best configuration. Currently two flags are supported:

ACCFFT_ESTIMATE: Minimal/no tuning. This option does not over write the input array data.
ACCFFT_MEASURE: Tunes for local FFT execution algorithm, as well as global transposes to reduce communication time. Note that with this flag, the setup will overwrite the input array data to perform the tunings.