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clAmdFft appears to give incorrect results for 2^20 and 2^21 length vectors

Question asked by myrv on Jun 25, 2012
Latest reply on Jul 3, 2012 by bragadeesh



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.