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-tp343...
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@gmail.com mailto:nicolas.cellier.aka.nice@gmail.com> wrote:
2011/1/25 Andreas Raab <andreas.raab@gmx.de <mailto:andreas.raab@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