Someone recently estimated to me in a BOTE calculation that [ ] is 10x slower. That is, this hamstrings the screamingly fast boyer-moore literal string matching part of the regex engine and compiles /xxx[ ]xxx/ down to exact("xxx"), anyof(" "), exact("xxx") where it was originally exact( "xxx xxx" ).

You've changed the regex from one for a seven character literal to one that contains two three character literals. That changes how the engine matches and it changes how quickly the BM part of the engine can either discard entirely or find suitable candidates. It also causes more overhead because three ops have to be executed instead of just one.

I'm asserting that [ ] is pretty to look at but has serious consequences to the regexp's performance. I wouldn't ordinarilly choose the pretty version in that case. I rarely ever use /x though so I don't need to escape my spaces.

⠤⠤ ⠙⠊⠕⠞⠁⠇⠑⠧⠊

In reply to Re^3: regex problem by diotalevi
in thread regex problem by Otogi

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.