[Pdx-pm] bit wise comparison

[Eric Wilhelm]

# from Tom Keller
# on Thursday 11 February 2010 12:22:

>$in = 'ACCTCCTCCTCGAGTATGTG';
>$tgt = 'TATCTTGCGCCGGAGATAAT';
>$mask = pack("A*",$in)^pack("A*",$tgt);
>$matches = $mask =~ tr/"\x0"/"\x0"/;

I get warnings from the quotes (") in the tr//.  You *did* enable 
warnings, right?  :-D

An interesting, but slower trick would let you know where the matches 
are in a more straightforward way.

  $tgt =~ s/(.)/(?:($1)|.)/g;
  my @matches = $in =~ m/^$tgt/;

But why pack() ASCII characters into "A*" ASCII characters?  You should 
get a same and faster result with:

  my $mask = $in ^ $tgt;
  my $matches = $mask =~ tr/\x0//;

--Eric
-- 
"You can't win. You can't break even. You can't quit."
--Ginsberg's Restatement of the Three Laws of Thermodynamics
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