Re: Linus' sha1 is much faster!

[Linus Torvalds]

On Sun, 16 Aug 2009, Giuseppe Scrivano wrote:
> 
> My GCC version is "gcc (Debian 4.3.3-14) 4.3.3" and the CPU is: Intel(R)
> Pentium(R) D CPU 3.20GHz.

Netburst is very sensitive to random spill effects, and you can basically 
tune things by just code shuffling that just has random effects on the 
generated asm code.

> I also spent some time trying to improve the gnulib SHA1 implementation
> and it seems a lookup table can improve things a bit.

I pretty much can guarantee you that it improves things only because it 
makes gcc generate crap code, which then hides some of the P4 issues.

I'd also suggest you try gcc-4.4, since that apparently fixes some of the 
oddest spill issues.

                        Linus