[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

bug#17229: [PATCH 2/2] grep: speed-up by using memchr() in Boyer-Moore s

From: Eric Blake
Subject: bug#17229: [PATCH 2/2] grep: speed-up by using memchr() in Boyer-Moore searching
Date: Fri, 25 Apr 2014 10:22:42 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0

On 04/25/2014 10:14 AM, Norihiro Tanaka wrote:
> grep 2.18 is slow for below, because always d == 1.
>   $ env LANG=C src/grep jk k
> Therefore, I wrote 
> 0001-grep-speed-up-by-using-memchr-in-Boyer-Moore-searchi.patch.
> When `d' is small, speeds up.  memchr() is faster than or as fast as
> delta1 search even when `d' is sufficiently large.
> However, this patch can't apply to case-insensitive matching.
> In fast, when `d' is large as following case, memchr_trans() imitated
> memchr() will occur slowdown.

Gnulib includes a memchr2() interface, which efficiently searches for
one of two byte values across a known memory length.  It is not quite as
fast as optimized assembly memchr for a single byte search, but when
searching for two bytes in parallel, it is hands down faster than two
sequential memchr() operations or any naive byte-by-byte comparisons.  I
suspect that using memchr2() for case-insensitive searches may allow you
a speedup when searching for (the first byte of) two potential matches
in the search string to the first character of a case-insensitive pattern.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Attachment: signature.asc
Description: OpenPGP digital signature

reply via email to

[Prev in Thread] Current Thread [Next in Thread]