[Vm-dev] Portability problems: compiler flags

[Andreas Raab]

On 4/10/2011 18:35, Mariano Martinez Peck wrote:
> 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?

gcc 3.x accepts -mno-fused-madd fine.

Cheers,
   - Andreas

>
> Thanks
>
> Mariano
>
> On Tue, Jan 25, 2011 at 9:05 PM, Nicolas Cellier 
> <nicolas.cellier.aka.nice at gmail.com 
> <mailto:nicolas.cellier.aka.nice at gmail.com>> wrote:
>
>
>     2011/1/25 Andreas Raab <andreas.raab at gmx.de
>     <mailto: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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