[Bioperl-l] string comparision mismatches and matches

Torsten Seemann torsten.seemann at infotech.monash.edu.au
Thu Feb 11 06:52:12 EST 2010

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

Impressive! Not often you see pack() let alone exclusive-or with a
scalar context tr// thrown in for good measure!

For those who don't follow what it is doing, here is my (possibly
wrong) interpretation: The pack() is converting each of the two (equal
length) strings into a byte set. A bit-wise exclusive-or (XOR) is
performed between these two byte sets. This will create bytes of value
zero (0) where they were the same, and non-zero where they were
different. The tr// then counts how many of the bytes were zero (\x0
is ascii zero).

I'll just assume it is more efficient than for/substr/eq :-)

--Torsten Seemann
--Victorian Bioinformatics Consortium, Dept. Microbiology, Monash
University, AUSTRALIA

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