[fpc-devel] 64 Bit / 32 Bit

Florian Klaempfl florian at freepascal.org
Thu Oct 4 13:31:30 CEST 2007

Michael Schnell schrieb:
>> No. This was MMX. SSE is always separate.
> How does an old OS that does not know about SSE do the task switch ?

It doesn't. You can't use SSE on e.g. unpatched Win95 or WinNT.

>> No, it's cutting of old hindering stuff.
> 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.

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