I use it a lot in perlgolf, but not in real code since it tends to destroy the string (notice that your code does, though you tried to avoid that I think). In real code using a while on a regex in scalar context is slightly faster and not so dangerous. When programming an inner loop and trying to be blazingly fast, you also should avoid things like $1.$2 since constructing a new value is a relatively expensive operation in perl. So the regex variant I'd use is: 
$count{$1}++ while $genome =~ /(?=(..))./g

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But this is still twice as slow as the substr() variant.

In reply to Re: using s/// as map? by thospel
in thread how can I speed up this perl?? by Anonymous Monk

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