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Perl: the Markov chain saw

Re^3: Picking up Values By Group

by BrowserUk (Pope)
on Feb 04, 2009 at 11:47 UTC ( #741349=note: print w/replies, xml ) Need Help??

in reply to Re^2: Picking up Values By Group
in thread Picking up Values By Group

instead of calling index repeatedly.

The tradeoff is:

  • scanning a 4 character string for a single character.
  • hashing a single character to a 32-bit hash and then performing a modulo 4 operation upon it.

Which actually favours the former:

#! perl -slw use strict; use Benchmark qw[ cmpthese ]; our %lookup = ( A=>0, B=>1, C=>2, D=>3 ); our $input = 'ACGT' x 1000; cmpthese -1, { index => q[ our( %lookup, $input ); my $n; $n = index "ACGT", $_ for split '', $input; ], hash => q[ our( %lookup, $input ); my $n; $n = $lookup{ $_ } for split '', $input; ], }; __END__ c:\test>junk5 Rate hash index hash 107/s -- -21% index 135/s 27% --

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