Re: Linus' sha1 is much faster!

From: Giuseppe Scrivano <gscrivano@gnu.org>
Date: Aug 17, 2009, 10:51 UTC
Message-ID: <8763cmemsa.fsf@master.homenet>
In-Reply-To: <4A88B80D.40804@draigBrady.com>

Pádraig Brady <P@draigBrady.com> writes:

>   -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions
>   -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i586
>   -mtune=generic -fasynchronous-unwind-tables -D_GNU_SOURCE=1

thanks. I did again all tests on my machine using these same options. I repeated each test 6 times and I took the median without consider the first result. Except the first run that it is not considered, I didn't report a big variance on results of the same test.

gcc 4.3.3

gnulib sha1: real 0m2.543s gnulib sha1 lookup: real 0m1.906s (-25%) linus's sha1: real 0m2.468s (-3%) linus's sha1 no asm: real 0m2.289s (-9%)

gcc 4.4.1

gnulib sha1: real 0m3.386s gnulib sha1 lookup: real 0m3.110s (-8%) linus's sha1: real 0m1.701s (-49%) linus's sha1 no asm: real 0m1.284s (-62%)

I don't see such big differences in asm generated by gcc 4.4.1 and gcc 4.3.3 to explain this performance difference, what I noticed immediately is that in the gcc-4.4 generated asm there are more "lea" instructions (+30%), but I doubt this is the reason of these poor results. Anyway, I haven't yet looked much in details.

Cheers, Giuseppe