Date: Sun, 12 Feb 2017 16:42:19 +0100 From: Szabolcs Nagy <nsz@...t70.net> To: musl@...ts.openwall.com Subject: Re: catrig * James Cloos <cloos@...loos.com> [2017-02-11 23:59:46 -0500]: > There was a recent post on one of the freebsd lists about Stephen > Montgomery-Smith's catrig routines: > > http://faculty.missouri.edu/~stephen/software/#catrig > > which is based on the paper "Implementing the complex arcsine and > arccosine functions using exception handling" by T. E. Hull, Thomas > F. Fairgrieve, and Ping Tak Peter Tang, published in ACM Transactions on > Mathematical Software, Volume 23 Issue 3, 1997, Pages 299-335, > http://dl.acm.org/citation.cfm?id=275324. > > It looks to be the most accurate catrig code availalbe. Stephen writes > that tests indicate that both the real and imaginary parts of the > results are good to within 4 ULP, that catrigl.c supports both 80 bit and > 128 bit long double but that the float version is occasionally slightly > worse that 4 ULP. > > I don't know how much interest the musl community has in better accuracy > for libm, but in case there is interest Stephen's code looks like a good > choice. > > And I see musl already uses freebsd libm code for some of the complex trig. glibc and freebsd have precise complex math, i think musl should do it too, but i dont yet have the testing infrastructure musl has slightly different tradeoffs than freebsd so we cannot take the code as is: i prefer to do bithacks in a more explicit way, volatile hacks are not allowed and code size matters so unnecessary optimization/special case branches should be pruned. it was low prio because i dont know of any actual users of these functions (for a long time glibc and bsd implementations were bad so nobody could rely on the precision of these functions).
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