On Fri, 09 Jan 2015 15:36:21 +0000 FrankLike via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com> wrote:
> On Friday, 9 January 2015 at 14:03:21 UTC, ketmar via
> Digitalmars-d-learn wrote:
> > On Fri, 09 Jan 2015 13:54:00 +0000
> > Robert burner Schadek via Digitalmars-d-learn
> > <digitalmars-d-learn@puremagic.com> wrote:
> >
> >> On Friday, 9 January 2015 at 13:25:17 UTC, ketmar via
> >> Digitalmars-d-learn wrote:
> >> > if you *really* concerned with speed here, you'd better
> >> > consider using
> >> > regular expressions. as regular expression can be
> >> > precompiled and then
> >> > search for multiple words with only one pass over the source
> >> > string. i
> >> > believe that std.regex will use variation of Thomson
> >> > algorithm for
> >> > regular expressions when it is able to do so.
> >>
> >> IMO that is not sound advice. Creating the state machine and
> >> running will be more costly than using canFind or indexOf how
> >> basically only compare char by char.
> >>
> >> If speed is really need use strstr and look if it uses sse to
> >> compare multiple chars at a time. Anyway benchmark and then
> >> benchmark some more.
> > std.regex can use CTFE to compile regular expressions (yet it
> > sometimes
> > slower than non-CTFE variant), and i mean that we compile
> > regexp before
> > doing alot of searches, not before each single search. if you
> > have alot
> > of words to match or alot of strings to check, regexp can give
> > a huge
> > boost.
> >
> > sure, it all depends of code patterns.
> import std.regex;
> auto ctr = ctRegex!(`(home|office|sea|plane)`);
> auto c2 = !matchFirst("He is in the sea.", ctr).empty;
> ----------------------------------------------------------
> Test by auto r = benchmark!(f0,f1, f2, f3,f4,f5)(10_0000);
>
> Result is :
> filter is 42ms 85us
> findAmong is 37ms 268us
> foreach indexOf is 37ms 841us
> canFind is 13ms
> canFind indexOf is 39ms 455us
> ctRegex is 138ms
1. stop doing captures in regexp, this will speedup the comparison.
2. your sample is very artificial. i was talking about alot more
keywords and alot longer strings. sorry, i wasn't told that clear
enough.
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