------- Comment #7 from dave at hiauly1 dot hia dot nrc dot ca 2006-05-23
16:28 -------
Subject: Re: __builtin_nanf("") doesn't return a _quiet_ nan on parisc
> ------- Comment #6 from rth at gcc dot gnu dot org 2006-05-23 15:00 -------
> (In reply to comment #4)
> > This isn't a target bug as far as I can tell. The value generated
> > by __builtin_nanf("") as shown by Nan2.c is 0x7fc00000. The same
> > value is printed on x86. This is a signaling NaN. Positive quiet
> > NaNs range between 0x7f800001 and 0x7fbfffff.
>
> Incorrect. The canonical QNaN on x86 (and most other targets) is
> 0x7fc00000. It would seem that PA has the same reversed quiet bit
> as MIPS. See real_format->qnan_msb_set and mips_ieee_single.
Interesting. The HP architecture docments for PA 1.1 and 2.0
state that PA-RISC fully conforms to ANSI/IEEE Std 754-1985, so
I presume that this isn't specified (don't have a copy of the
spec handy), so there's no actual canonical format. I see this
was something of a point of contention in 754R meetings.
Google tells me that MIPS didn't discriminant in early processors,
then used the same convention as PA-RISC, and finally switched again.
So, don't much like calling this the "mips" format.
Dave
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27627
