[Mono-bugs] [Bug 464135] New regexp compiler much slower (~80x) than the old one with certain regexps

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https://bugzilla.novell.com/show_bug.cgi?id=464135

User vargaz at gmail.com added comment
https://bugzilla.novell.com/show_bug.cgi?id=464135#c1





--- Comment #1 from Zoltan Varga <vargaz at gmail.com>  2009-01-07 09:29:43 MST ---
This is caused by the following regex:
                        css = Regex.Replace(css,
@"(?<=color\s*:\s*.*)\#(?<hex>f00)\b", "red", RegexOptions.IgnoreCase);

I have no idea why this runs fast either on .net, or in the old interpreter.
It contains a 'positive lookbehind': (?<=color\s*:\s*.*) which ends with a .*,
so for each text position, it matches all substrings which ends at that
position,
ie. for ABCD, it tries:

A
B
AB
C
BC
ABC
D
CD
BCD
ABCD

the input file is 32k characters long.


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