Date: Sun, 15 Aug 2021 00:45:12 +0200 From: Szabolcs Nagy <nsz@...t70.net> To: Damian McGuckin <damianm@....com.au> Cc: musl@...ts.openwall.com Subject: Re: [PATCH #2] Properly simplified nextafter() * Damian McGuckin <damianm@....com.au> [2021-08-14 14:07:34 +1000]: > On Fri, 13 Aug 2021, Stefan Kanthak wrote: > > > It may be possible to reduce the number of such ops too; not sure. But > > > there's no way to eliminate them. > > Replacing the second FORCE'd expression with > > FORCE((ux.f + x) * (0x1.0p-52 * 0.25)); > > eliminates one floating point OP, assuming the optimiser does the right > thing to > > epsilon / 4 > > in the expression. Some preliminary testing seems to suggest that the same > exceptions get raised. > > > It's definitely possible to do a strength reduction and get rid of the > > multiplications. > > But then how is the exception still raised, or are we talking soft FP? that does not work, i think. but the subnormal result case is not worth optimizing. (or rather, i prefer to optimize cold code paths for size)
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