[Vm-dev] Portability problems: compiler flags

[Mariano Martinez Peck]

Sorry for arriving late to the thread. I have a simiar problem now trying to
compile Cog in a Windows box with MinGW.

The problem is described in another thread:
http://forum.world.st/Cannot-generate-VM-in-Windows-with-CMake-and-Git-tp3434566p3434566.html

So...if we remove "-mno-fused-madd"  from windows confs like
CogMsWindowsConfig, then Corquet wouldn't behave correctly ?  but if we keep
them, it is difficult to compile in some platforms. So...I wonder, I am the
only one trying to compile this on Windows?  Who do the Croquet guys do to
compile with this flag in Windows?

Thanks

Mariano

On Tue, Jan 25, 2011 at 9:05 PM, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> wrote:

>
> 2011/1/25 Andreas Raab <andreas.raab at gmx.de>:
> >
> > On 1/25/2011 11:38 AM, Igor Stasenko wrote:
> >>>
> >>> Squeak uses highly unportable flag "-mno-fused-madd".
> >>> It isn't present in many systems, even those using GCC,
> >>> since many systems use older compilers.
> >>>
> >>> Also, why do you build fdlibm? It is old stuff that works not so well,
> >>> we have better libm. Is there a way to use our libm?
> >>>
> >> I asked  same question few weeks ago.
> >> Check mailing list archive for discussion.
> >> In short: differrent libm implementations work differently and some
> >> have bad support of IEEE standard.
> >
> > Actually, that's not quite the point. The issue is that Croquet requires
> > bit-identical computations including floating point. For FPU
> computations,
> > the use of -mno-fused-madd avoids the use of the fused multiply-add
> > operation by compilers which support it which would generate different
> > results from compilers not using fused madd.
> >
> > The usage of fdlibm is similar. As Nicolas has pointed out elsewhere,
> fdlibm
> > is in some cases actually inferior of the platform libms (one might say
> > outright broken) but the requirement for the usage in Croquet isn't
> really
> > whether it's "correct" or "good". The requirement is bit-identical
> results
> > across all platforms. The results can be wrong as long as they are
> > consistently wrong. But they mustn't be different.
> >
>
> Yes, I was disappointed by exp(1), but fdlibm sin(pi+epsilon) is far
> far superior to i86 hardwired answer (i86 approximation of pi is well
> known to be poor).
>
> Nicolas
>
> > Having said that, for your regular Squeak VM (i.e., not requiring
> > bit-identical floating point results) there really isn't a requirement to
> > use either -mno-fused-madd or fdlibm.
> >
> > Cheers,
> >  - Andreas
> >
>



-- 
Mariano
http://marianopeck.wordpress.com
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