Re: [PATCHES] TODO item: Implement Boyer-Moore searching (First time hacker) - Mailing list pgsql-hackers

From Tom Lane
Subject Re: [PATCHES] TODO item: Implement Boyer-Moore searching (First time hacker)
Date
Msg-id 6183.1220761607@sss.pgh.pa.us
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In response to Re: [PATCHES] TODO item: Implement Boyer-Moore searching (First time hacker)  ("David Rowley" <dgrowley@gmail.com>)
Responses Re: [PATCHES] TODO item: Implement Boyer-Moore searching (First time hacker)  ("David Rowley" <dgrowley@gmail.com>)
List pgsql-hackers
"David Rowley" <dgrowley@gmail.com> writes:
> I've made the discussed changes. Also updated the benchmark results.
> http://www.unixbeast.com/~fat/8.3_test_v1.3.xls

Applied with revisions; mostly cosmetic except for one point.  I
realized after studying the code a bit more that B-M cannot possibly win
for a single-character pattern (needle), since the skip distance must
always be 1 in that case.  The fact that it seemed to keep up at that
length has to be because the original coding included a strncmp call
inside the innermost loop, which likely prevents the compiler from
optimizing that loop really tightly.  But the strncmp wasn't doing
anything anyway for the case of pattern length = 1.  So what I committed
special-cases pattern length 1 to be a naive search with a *very* tight
inner loop.  I think it's worth troubling over this case because a
common usage is split_to_array and suchlike with single-character
delimiters.
        regards, tom lane


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