Messages in this thread | | | Date | Wed, 15 Jun 2005 16:34:59 +0100 (BST) | From | "Maciej W. Rozycki" <> | Subject | Re: .../asm-i386/bitops.h performance improvements |
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On Wed, 15 Jun 2005 cutaway@bellsouth.net wrote:
> In find_first_bit() there exists this the sequence: > > shll $3,%%edi > addl %%edi,%%eax > > LEA knows how to multiply by small powers of 2 and add all in one shot very > efficiently: > > leal (%%eax,%%edi,8),%%eax
Be careful about model-specific penalties from using certain address modes and AGIs when using "lea" for such calculations.
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