Too much worrisome to be true?!!?

-------- Messaggio originale -------- Oggetto: Re: kern/133583: [libm] fma(3) does not respect rounding mode using extended precision Data: Fri, 3 Dec 2010 07:02:04 GMT Mittente: das@FreeBSD.org A: abramo.bagnara@gmail.com, das@FreeBSD.org, freebsd-bugs@FreeBSD.org

Synopsis: [libm] fma(3) does not respect rounding mode using extended precision

State-Changed-From-To: open->closed State-Changed-By: das State-Changed-When: Fri Dec 3 07:01:28 UTC 2010 State-Changed-Why: Thanks for the report! This limitation is described in the source for fma(), and unfortunately, it is unlikely to ever change. There are several reasons:

- We are a long way from having the necessary compiler support to make dynamic precision changes work as expected. - Dynamic FPU precision changes aren't officially supported, and fpsetprec() has been documented as deprecated for many years. - The only supported architecture that can have this problem due to dynamic precision changes is i386, and even then only for non-SSE2 builds. - The cost and complexity associated with making every function in libm detect and adapt to dynamic precision changes is prohibitive.

I have updated the manpage for fpsetprec() to explain that changing the FPU precision isn't supported by the compiler or libraries.

http://www.freebsd.org/cgi/query-pr.cgi?pr=133583