Subject: Re: -mieee option
To: Anders Magnusson <firstname.lastname@example.org>
From: Chris G. Demetriou <email@example.com>
Date: 01/14/1999 10:38:11
Anders Magnusson <firstname.lastname@example.org> writes:
> > Indeed, NetBSD/alpha does not support IEEE-conformant arithmetic.
> Eh, what? How does the Alpha math lib work in that case???
There's a difference between "approximately IEEE" or "uses IEEE
formats and many operations" and "IEEE conformant" or "complete
implementation" for any nearly-strict sense of the word "conformant."
basically, NetBSD/alpha supports what the alpha hardware will do for
it. That is things like:
* floating point formats
* basic operations
but does _not_ cover some of the corner cases re: exceptions and NaNs,
and (if i recall) doesn't completely cover some of the things that
some software likes to use (e.g. denormalized numbers).
i.e. basic math works, but if you're actually on the exception and/or
denorm, or other 'somewhat near the corner'-case IEEE math,
NetBSD/alpha won't do it.
Like i said, i'm approximately clueless when it comes to FP stuff. If
you're interested in what the alpha architecture pushes off to
software completion (i.e. the OS and libraries), take a look at the
Alpha Architecture Reference Manual.
Looks like they've got the abridged (free) version of that up on the
Interesting stuff for FP math fans can be found in:
section 2.2.6 "IEEE Floating-Point Formats"
section 4.7 "Floating-Point Instructions", especially
section 4.7.10 "IEEE Standard" which describes
the alpha architecture's behaviour for IEEE
operations which are implementation dependent.
appendix B "IEEE Floating-Point Conformance," which
begins: "A subset of IEEE Standard for Binary
Floating-Point Arithmetic (ANSI/IEEE Standard
754-1985) is provided in the Alpha
floating-point instructuctions. This appendix
describes how to construct a complete IEEE
You'll find that they describe much better than I do what the hardware
does and doesn't do, and what the OS should do to make up for it. 8-)
Chris Demetriou - email@example.com - http://www.netbsd.org/People/Pages/cgd.html
Disclaimer: Not speaking for NetBSD, just expressing my own opinion.