Re: 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%   --
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Comment on Re: How can I tell if a number is a power of 2? Download Code

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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% -- [download] `2;0 juerd@ouranos:~$ perl -e'undef christmas' Segmentation fault 2;139 juerd@ouranos:~$` [download]	[reply] [d/l] [select]

Replies are listed 'Best First'.

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

#!/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]

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