Such code irks me. It always has to perform three modulus operations, even while in 99% of the cases it doesn't have to. The Date::Leapyear code irks me too, as it tests the rare cases first. I prefer code like the following: 
sub is_leap {
    my $year = shift;
    return 0 if $year % 4;
    return 1 if $year % 100;
   !($year % 400)
}

[download]

That code does one modulus operation in 75% of the cases, two modules operations in 24% of the cases, and only in 1% of the cases, it does 3 modulus operations.

A benchmark shows the expected results. The code that always does three modulus operations is the slowest - the code that on averages does the least modulus operations is the fastest. 

#!/usr/bin/perl

use strict;
use warnings;

use Benchmark qw /cmpthese/;

sub isleap {
    my ($year) = @_;
    return 1 if (( $year % 400 ) == 0 ); # 400's are leap
    return 0 if (( $year % 100 ) == 0 ); # Other centuries are not
    return 1 if (( $year % 4 ) == 0 ); # All other 4's are leap
    return 0; # Everything else is not
}

sub browseruk {
    my ($year) = @_;
    not $year % 4 xor $year % 100 xor $year % 400;
}

sub abigail {
    my ($year) = @_;
    return 0 if $year % 4;
    return 1 if $year % 100;
    !($year % 400)
}


cmpthese -10 => {
    isleap    => 'my $v = isleap    $_ for 1800 .. 2199',
    browseruk => 'my $v = browseruk $_ for 1800 .. 2199',
    abigail   => 'my $v = abigail   $_ for 1800 .. 2199',
};

__END__
Benchmark: running abigail, browseruk, isleap, each for at least 10 CP
+U seconds...
   abigail: 11 wallclock secs (10.90 usr +  0.00 sys = 10.90 CPU) @ 18
+43.58/s (n=20095)
 browseruk: 10 wallclock secs (10.48 usr +  0.01 sys = 10.49 CPU) @ 14
+09.82/s (n=14789)
    isleap: 11 wallclock secs (10.76 usr +  0.01 sys = 10.77 CPU) @ 14
+54.04/s (n=15660)
            Rate browseruk    isleap   abigail
browseruk 1410/s        --       -3%      -24%
isleap    1454/s        3%        --      -21%
abigail   1844/s       31%       27%        --

[download]

Abigail

In reply to Re: Anyone use "xor" in conditionals? by Abigail-II
in thread Anyone use "xor" in conditionals? by bsb

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