Re: [Grep-devel] [PATCH 2/2] grep: speed up Aho-Corasick when at most 2 bytes

[Paul Eggert]

On 01/30/2017 02:24 PM, Jim Meyering wrote:
> > >    yes $(printf 0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c) | head -1000000>inp
> > >
> > >    time -p src/grep -F -e 0b -e ab inp

> On an idle 3-year old i7-4770S with plenty of RAM, I ran the following
>   commands before and after the patch, taking the best time out of 10:
>
>    yes $(printf 0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c0c) | head -20000000 >inp
>    for i in $(seq 10); do env time src/grep -F -e 0b -e ab inp; done
>
> Before the patch, the best was 03.39elapsed.
> After, it was 03.13elapsed, i.e., taking 7.6% less time.
> I compiled with -O2 and a very recent gcc: version 7.0.1 20170127
> (experimental) (GCC)

I tried a quite-different platform and got about a 25% speedup. This is 
an old Sun Fire 280R with an 750 MHz UltraSPARC III, compiled with 
32-bit Oracle Studio 12.5 (2016) with -xO4 and running Solaris 10.

Since the patch helps performance significantly on some platforms and 
doesn't seem to hurt on any, and since it's a small patch that is 
unlikely to break things, I installed it.