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
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