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Postings from March 2014
On Fri, Mar 21, 2014 at 06:01:01AM -0700, Zefram wrote:
> $ perl5.19.10 -lwe 'print "wibble" =~ /\Awibble\z/m ? "yes" : "no"'
> no
> $ perl5.19.9 -lwe 'print "wibble" =~ /\Awibble\z/m ? "yes" : "no"'
> yes
I've just bisected this to the following plausible-looking commit:
d0d4464849e2b30aee89c175ccb5465795de10ce is the first bad commit
commit d0d4464849e2b30aee89c175ccb5465795de10ce
Author: David Mitchell <davem@iabyn.com>
Date: Tue Mar 18 20:15:27 2014 +0000
re_intuit_start(): reduce scope of /^...$/m test
Intuit has a quick reject test for a fixed pattern that is anchored at
both ends. For example, with the pattern /^abcd$/, only the exact strings
"abcd" or "abcd\n" will match; anything else, and the match immediately
fails.
A fix for [perl #115242] correctly made intuit skip the test in the
presence of //m, since in this case the $ doesn't necessarily correspond
to the end of the string.
However, the fix was too wide in scope; it caused //m patterns to skip
searching for a known string anchored just at the start, as well as one
anchored at both ends.
With this commit, the following code now runs in a few milliseconds rather
than a few seconds on my machine:
$s = "abcdefg" x 1_000_000;
$s =~ /(?-m:^)abcX?fg/m for 1..100;
Tom
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