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

[larryk]

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%   --

[Juerd]

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:~$