That seems to work. !5 seconds instead of 53 for the alternation is much more reasonable. Still doesn't beat the two pass method, but there is probably a break point somewhere. 

c:\test>junk31 836952.log
Benchmark:
timing 1 iterations of
 AAtwo_pass, BBtwo_string, CCone_string
...

two pass: 10
AAtwo_pass:  7 wallclock secs ( 5.60 usr +  0.83 sys =  6.43 CPU) @  0
+.16/s (n=1)

            (warning: too few iterations for a reliable count)

two string: 10
BBtwo_string: 15 wallclock secs (14.35 usr +  0.94 sys = 15.29 CPU) @ 
+ 0.07/s (n=1)

            (warning: too few iterations for a reliable count)

one string: 7
CCone_string: 16 wallclock secs (14.76 usr +  0.73 sys = 15.49 CPU) @ 
+ 0.06/s (n=1)

            (warning: too few iterations for a reliable count)

[download]

I'm still puzzled why the two pass takes less time than the one string, but the numbers are right and I can't anything major wrong with the benchmark?

In reply to Re^3: Unefficient Regexp 'Matching this or that' by BrowserUk
in thread Unefficient Regexp 'Matching this or that' by pelagic

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.