More info: EGCS-971016 on Solaris2.5/UltraSparc

[Jakub Jelinek]

> Hi-
> 
> I ran a bunch of tests with the sun CC compiler and I found out that
> the only significant feature (for my platform) that their compiler
> uses that's not in EGCS (yet) is is the -fns option:
> 
>      -fns         Turn on the SPARC nonstandard floating-point mode (SPARC)
> 
> Does anyone know what this is?  I don't know if this is a trivial
> thing or a tricky one.

The FPU on the UltraSPARC is not working with subnormal operands and/or
results. Instead of that, it traps to the operating system, so that the
results can be correct according to IEEE754. That may be slow, so NS says
that all subnormal operands and all subnormal results will be replaced by
zeros with the same sign (and if requested IEEE754 inexact/underflow traps
will be signalled).

I'm not 100% sure what does the -fns option in SunPRO exactly, probably it
just chooses different startup files and maybe makes some differences in the
code. Could you by change sent me privately assembly output of some short
FPU intensive program compiled with and without -fns?

Cheers,
    Jakub
___________________________________________________________________
Jakub Jelinek | jj@sunsite.mff.cuni.cz | http://sunsite.mff.cuni.cz
Administrator of SunSITE Czech Republic, MFF, Charles University
___________________________________________________________________
Ultralinux - first 64bit OS to take full power of the UltraSparc
Linux version 2.0.30 on a sparc machine (291.64 BogoMips).
___________________________________________________________________