Hello, I realize that I'm a little late to comment about this, but I think the formula used for tanh should be changed again. Specifically, as suggested by Roland
On Fri, Dec 9, 2016 at 5:41 AM, Roland Scheidegger <srol...@vmware.com> wrote: > btw I'm wondering if some vendors wouldn't implement that with slightly > simplified formula, e.g. (e^2x - 1) / (e^2x + 1) (this is what nvidia > used for cg apparently according to docs, saving one of the > exponentials). Might be worse for accuracy though (and won't solve this > problem, though it would now only need a one-sided clamp). Another option is the 1 - 2/(1+expf(2x)), or even better 1 - 2/(2+expm1f(2x)).. I've run some tests and this seems to have the same accuracy as the one mentioned by Roland, with the bonus benefit of not needing any clamping. The accuracy seems to actually be better than the direct evaluation (difference over sum of exps), except around 0 (say, when abs(x) < 1). I've found the relative error away from 0 to be typically in the same order of magnitude as the error in tanhf() itself (compared to tanh()) , and generally less than machine epsilon.. I'm currently looking at options to improve the accuracy without clamping and without excessive additional computations, might propose a patch in the next couple of days. Just one question though —not knowing much of the shader language, can I expect expm1 to be available? -- Giuseppe "Oblomov" Bilotta _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
