Hi Pádraig,

I tried to reproduce your results but I wasn't able to do it.  The
biggest difference on a 300MB file I noticed was approximately 15% using
on both implementations -O2, and 5% using -O3.
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.

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

Can you please try the patch that I have attached and tell me which
performance difference (if any) you get?

Thanks,
Giuseppe