Re: Algoritmic Complexity Attacks and 2.4.20 the dcache code

[William Lee Irwin III <wli@holomorphy.com>]

From: Alex Riesen <alexander.riesen@synopsys.COM>
Date: Fri, 30 May 2003 10:59:01 +0200
>        static
>        int hash_3(int hi, int c)
>        {
>    	return (hi + (c << 4) + (c >> 4)) * 11;
>        }
>    gcc-3.2.1 -O2 -march=pentium
>  ...   
>    It is not guaranteed to be this way on all architectures, of course.
>    But still - no multiplications.

On Fri, May 30, 2003 at 02:00:40AM -0700, David S. Miller wrote:
> Indeed, I'd missed this.  GCC will emit the constant multiply
> expansion unless the multiply cost is set VERY low.

If the strength reduction situation changes to being properly handled
by gcc for most/all 64-bit arches, include/linux/hash.h can lose a #ifdef.


-- wli