[rescue] OS X is certified UNIX
Charles Shannon Hendrix
shannon at widomaker.com
Sun Jun 17 13:26:53 CDT 2007
Meelis Roos wrote:
>> Another issue is that in 64-bit mode you do not have an FPU. The FPU is
>> disabled, and all math is done with SIMD instructions, which are generally
>> faster and not as prone to bottlenecks common to the x87 FPU.
> Sure about this - got any quote of specification? AFAIK gcc defaults to
> SSE2 floating pint on AMD64 but it's just the default, it seems to be
> still able to use FPU if someone so chooses.
Actually, I got that from IBM and AMD.
However, I did misread it.
AMD does say that the FPU is going away, but not yet.
Saving FPU registers in long mode is a performance hit, so some OS do not do it,
which means you cannot use the FPU. Windows 64-bit edition for example.
So whether or not you can use the FPU in 64-bit mode depends on your OS, your
compiler, and when AMD and Intel remove it in the future.
shannon | An Irishman is never drunk as long as he can hold onto
| one blade of grass and not fall off the face of the earth.
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