On Wed, Nov 07, 2018 at 10:34:30PM +0000, Wilco Dijkstra wrote: > Hi Jeff, > > > So if we're going from 0->2 ULPs in some cases, do we want to guard it > > with one of the various options, if so, which? Giuliano's follow-up > > will still have the potential for 2ULPs. > > The ULP difference is not important since the individual math functions > already have ULP of 3 or higher. Changing ULP error for some or all inputs > (like we did with the rewritten math functions) is not considered an issue as > long as worst-case ULP error doesn't increase.
But the max. error in sinh/cosh/atanh is less than 2 ULP, with some math libraries. It could be < 1 ULP, in theory, so sinh(atanh(x)) less than 2 ULP even. > The question is more like whether errno and trapping/exception behaviour > is identical - I guess it is not so I would expect this to be fastmath only. > Which particular flag one uses is a detail given there isn't a clear > definition > for most of them. And signed zeroes. Yeah. I think it would have to be flag_unsafe_math_optimizations + some more. Segher
