This looks to be about 10% faster on my dataset: 
foreach my $constant (keys %constants) {
    $string = join $constants{$constant}, split /$constant/, $string;
}

[download]
It's a lot less clear, though. Maybe if you build the regexes beforehand, you'll see a speed benefit? Look at the qr/// operator.

In reply to RE: How do I speed this up? by chromatic
in thread How do I speed this up? by Anonymous Monk

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