/foo(.*?)(foo|bar)/  &&  "bar" ne $2

##</code><code>##

    /foo(.*?)foo/  &&  $1 !~ /bar/

##</code><code>##

Benchmark: running japhy, obvious, tilly, and tye,
each for at least 3 CPU seconds (sorted fastest to slowest)...
   obvious:  3.13 CPU @ 77.96/s (n=244)
     tilly:  3.41 CPU @ 33.43/s (n=114)
       tye:  3.29 CPU @ 20.06/s (n=66)
     japhy:  3.02 CPU @ 10.60/s (n=32)

##</code><code>##

#!/usr/bin/perl -w

use strict;
use Benchmark;

my @pat= qw( fooxfoo  fooxbar  xfooxfoo  xfooxbar
             fooxfoox fooxbarx xfooxfoox xfooxbarx );
my @fill= ( "ba", "fo", "bf", "bafo", "babrar" );
@pat= map { my $fill= $_ x 1000; map { ( my $pat= $_ ) =~ s/x/$fill/g; $pat } @pat } @fill;

sub obvious {
    /foo(.*?)foo/  &&  $1 !~ /bar/
    and $1
}
sub tye {
    /foo(.*?)(bar|foo)/ && "bar" ne $2
    and $1
}
sub tilly {
    /foo((?:(?!bar).)*)foo/
    and $1
}
sub japhy {
    m{
      foo
      (             # save to $1
        [^b]*       # 0 or more non-b characters
        (?:
          (?>b+)    # 1 or more b's (NO BACKTRACKING!)
          (?:
            a(?!r)  # an 'a' NOT followed by an 'r'
            |       # or
            [^a]    # a non-a character
          )
          [^b]*     # 0 or more non-b characters
        )*          # that whole b... subset, 0 or more times
      )
      foo           # and foo
    }x
    and $1
}

sub checkthese {
    my( $sub, $hTests )= @_;
    my %res;
    for my $meth (  keys %$hTests  ) {
        my $res= $sub->( $hTests->{$meth} );
        for(  keys %res  ) {
            if(  $res ne $res{$_}  ) {
                warn "$meth and $_ disagree!\n";
            }
        }
        $res{$meth}= $res;
    }
}
checkthese( sub { join " ", map { $_[0]->() } @pat }, {
    tilly => \&tilly,
    japhy => \&japhy,
    tye => \&tye,
    obvious => \&obvious,
} );
timethese( -3, {
    obvious => sub { map obvious(), @pat },
    tye => sub { map tye(), @pat },
    tilly => sub { map tilly(), @pat },
    japhy => sub { map japhy(), @pat },
} );