Dear Monks!

I need to be able to tell, whether two lower-case strings differ at only one position, or they are the same. They must also be of the same length. That is

abab  -   abab     is OK
abab  -   abaa     is OK
abab  -   qrst     is not OK
abab  -   abba     is not OK
abab  -   ababa    is not OK

I need the fastest solution on Earth, since I have to do an enormous number of comparisions (for all two words of a fairly large dictionary). My solution is based on splitting the words into arrays and compare positionally, but it is painfully slow.

sub compare{
  return 0 unless length $_[0] == length $_[1];
  return 1 if $_[0] eq $_[1];
  my $diff = 0;
  my @l1 = split //, $_[0];
  my @l2 = split //, $_[1];
  for(my $i = 0; $i < scalar @l1; $i++){
    $diff++ if $l1[$i] ne $l2[$i];
    return 0 if $diff > 1;
  }
  return 1;
}
[download]

Could you make it much faster?

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