DMD2 out parameters
Don
nospam at nospam.com
Thu Dec 23 11:09:22 PST 2010
Pete wrote:
> Ok, i've done some more investigating and it appears that in DMD2 a float NaN is
> 0x7FE00000 (in dword format) but when it initialises a float 'out' parameter it
> initialises it with 0x7FA00000H. This causes an FPU trap which is where the time
> is going. This looks like a bug to me. Can anyone confirm?
>
> Thanks.
Yes, it sounds like a NaN-related peformance issue. Note, though, that
the slowdown you experience is processor-model specific. It's a penalty
of ~250 cycles on a Pentium 4 with x87 instructions, but zero cycles on
many other processors. (in fact, it's also zero cycles with SSE on
Pentium 4!).
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