On Tue, Dec 30, 2014 at 11:55 PM, Sylvain Munaut <[email protected]> wrote:
> If you need high, deterministic, quantifiable precision, you're > probably better off reimplementing the critical blocks yourself the > way you want. > > Most of the default blocks will have numerous optimization for speed > that can sacrifice precision. And this will actually depend on which > version of the volk kernel gets selected (generic / SSE / AVX / ....) > because they use different algorithm and opcodes and such. > > I'm pretty sure the rotator SIMD version has spurs because of the > periodic renormalization process, but in any case they're like more > than -130 dB down which makes them irrelevant for all but the most > demanding applications. > > Cheers, > > Sylvain Just as an aside - and a note for other folks who want to investigate differences between SIMD-optimized vs. generic kernels, VOLK does have an interesting (but perhaps not well-documented) feature in that if you set/create an environment variable called VOLK_GENERIC (e.g. 'export VOLK_GENERIC=1'), then the VOLK dispatcher will only call the generic implementation. This shows up in most GR and OOT QA tests automatically (at least in the Python-based QA tests) via the GrTest.cmake module. Doug -- Doug Geiger [email protected]
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