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%   --

[download]

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

[download]

In reply to Re: Re: How can I tell if a number is a power of 2? by Juerd
in thread How can I tell if a number is a power of 2? by larryk

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