Bug #1608: clFFT use of native_sin , native_cos can cause validation problems
experimental: -added alternative method for twiddle factor calc, using a smaller LUT (256 * float2 ) via Taylor series to 3rd order, seems to be almost as accurate as method with 2 bigger LUTs, but faster. -improved method w/ 2 bigger LUTs to use LUTs of float2 -improved method using slow sin/cos functions (now uses sincos combined function), still slow - preparaed plan struct to have method switchable at plan creation time. TODO: load smaller LUT for Taylor series approx into shared mem.
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