Subject: Re: [patch][0/5] powerpc: Add support to fully comply with IEEE-754standard

From: Segher Boessenkool <[email-masked]>
Date: Fri, 12 Jan 2007 13:03:53 +0100

> When floating-point underflow exceptions are disabled
> (SPEFSCR[FUNFE] is cleared) and the result of a floating-point 
> operation
> underflows, a signed zero result is produced.

You probably want to make at least this one tweakable
per-process; on some important algorithms (some FFTs
etc.) the results are perfectly acceptable with underflow-
to-zero and the performance difference is huge.  AltiVec
can do this per-process too, for example -- it has a
user register for setting this, you need some other
interface though.

Segher