Hello,

I'm using clAmdFft Version clAmdFft-1.6.244 (AMD APP SDK 2.6) on an Intel Xeon W3550 (running 64bit linux) using a Radeon HD 7970.

When performing large 1D single precision complex FFTs with a length of 2^20 or 2^21 the results appear to be incorrect.

Doing a forward then backward transform of a vector 2^20 or 2^21 elements long gives a RMSE of ~0.328 whereas a forward/backward transform of a 2^19 vector gives a RMSE of ~2.1717e-07. Strangely, going larger than 2^21 (i.e. 2^22) also appears to work correctly. Also, making the length a non pure power of 2 also appears to work (i.e. 2^19*3 returns the expected values).

Is this a known issue?

Any help or suggestions would be greatly appreciated.

Thanks.

Hi myrv,

Thanks for posting. I assume you are using the OpenCL GPU target (7970). What version of the graphics driver and APP SDK are you using? You can upgrade to the 1.8 version of the FFT libraries and see if it works for you. But please understand that the libraries still are 'beta'-only on the 7000 series cards. There are still some known issues in our software layers that prevents a full release.

We'll perform testing of those specific sizes locally and give an update if there are any more details.