Re: .../asm-i386/bitops.h performance improvements

[Maciej W. Rozycki]

On Wed, 15 Jun 2005 cutaway@xxxxxxxxxxxxx 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.

  Maciej
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