Re: improvement of index-calculation


"Guenther Wimpassinger" <gw_spam@xxxxxxxxx> schrieb

> mov ECX,[ESI+iShiftMaskY_sub_X_sub_Y32Bit]
> shl EAX,CL // EAX := "masked y" shl
> // iShiftMaskY_sub_X_sub_Y32Bit

I have a small problem with the above statments. specially
the shl. iShiftMaskY can be negativ. but shl treats cl always
as an unsigned value and shift EAX 255 times left.

do I have to check the and make a brachn like

if EAX<0
then
neg cl
shr eax,cl
else
shl eax,cl

what is the most efficient way?

TIA
Guenther



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