[fpc-devel] 64 Bit / 32 Bit

Daniël Mantione daniel.mantione at freepascal.org
Thu Oct 4 13:40:50 CEST 2007

Op Thu, 4 Oct 2007, schreef Florian Klaempfl:

> > If doing Mathematical calculations it of course is best to use the
> > format that offers the best accuracy when it's not slower. AFAIK the FPU
> > is not slower when doing 80 bit than when doing 64 bit (of course
> > loading/storing the values might take some additional cycles). So using
> > 80 seems like a very sensible option with the given X86 hardware (all
> > versions do support 80 bits).
> Always storing the FPU simply increases task switch time. Further, SSE
> is simply faster with 64 bit because of the easier to use register file
> and because more registers are available on 64 Bit CPUs.

Actually this is the whole core of the matter: Microsoft's  developers 
though they could save the task switch time by not storing the fpu.

However, later they discovered it was a huge security leak, and added the 
fpu store code.


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