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Re: How can I tell if a number is a power of 2?

by larryk (Friar)
on Jan 28, 2002 at 22:52 UTC ( #142148=note: print w/ replies, xml ) Need Help??


in reply to How can I tell if a number is a power of 2?

Of course implementation is everything:

#!perl use strict; use warnings; use Benchmark qw/cmpthese/; sub tye { my $x = shift; 0 == ( $x & ($x-1) ) ? 1 : 0; } sub tye2 { my $x = shift; !( $x & ($x-1) ); } cmpthese( -5, { tye => q!tye(rand 1000000)!, tye2 => q!tye2(rand 1000000)!, } ); __END__ Benchmark: running tye, tye2, each for at least 5 CPU seconds... tye : 6 wallclock secs ( 5.07 usr + 0.00 sys = 5.07 CPU) @ 200612 +.27/s (n=1016703) tye2: 6 wallclock secs ( 5.02 usr + 0.00 sys = 5.02 CPU) @ 225545 +.83/s (n=1131789) Rate tye tye2 tye 200612/s -- -11% tye2 225546/s 12% --


Comment on Re: How can I tell if a number is a power of 2?
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Re: Re: How can I tell if a number is a power of 2?
by Juerd (Abbot) on Jan 29, 2002 at 02:15 UTC
    And just because implementation is everything:
    #!/usr/bin/perl use strict; use warnings; use Benchmark qw/cmpthese/; sub tye2 { my $x = shift; !( $x & ($x-1) ); } sub tye3 { my ($x) = @_; !( $x & ($x-1) ); } sub tye4 { !( $_[0] & ($_[0] - 1) ); } cmpthese( -5, { tye2 => q!tye2(rand 1000000)!, tye3 => q!tye3(rand 1000000)!, tye4 => q!tye4(rand 1000000)!, } ); __END__ tye2:6wcs (5.30usr + 0.01sys = 5.31CPU) @ 384813.56/s (n=2043360) tye3:6wcs (5.07usr + 0.00sys = 5.07CPU) @ 381046.15/s (n=1931904) tye4:5wcs (5.42usr + 0.00sys = 5.42CPU) @ 493005.17/s (n=2672088) Rate tye3 tye2 tye4 tye3 381046/s -- -1% -23% tye2 384814/s 1% -- -22% tye4 493005/s 29% 28% --

    2;0 juerd@ouranos:~$ perl -e'undef christmas' Segmentation fault 2;139 juerd@ouranos:~$

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