Hi all, On Fri, Oct 19, 2018 at 09:21:07AM -0300, Giuliano Augusto Faulin Belinassi wrote: > > Did you enable FMA? I'd expect 1 - x*x to be accurate with FMA, so the > > relative error > > should be much better. If there is no FMA, 2*(1-fabs(x)) - (1-fabs(x))^2 > > should be > > more accurate when abs(x)>0.5 and still much faster. > > No, but I will check how to enable it if FMA is available. > I did a minor test with your formula and the precision improved a lot. > Here is an example for floats > > with input : = 9.99999880790710449218750000000000000000000000000000e-01 > cosh: before: = 2.04800000000000000000000000000000000000000000000000e+03 > cosh: after : = 2.04800024414062500000000000000000000000000000000000e+03 > cosh: mpfr : = 2.04800006103515897848424084406334262726138617589463e+03 > error before: = 6.10351589784842408440633426272613861758946325324235e-05 > error after : = 1.83105466021515759155936657372738613824105367467577e-04
Maybe I am crazy, or the labels here are wrong, but that looks like the error is three times as *big* after the patch. I.e. it worsened instead of improving. Segher
