#!/usr/bin/perl
use strict;
use warnings;
use POSIX;
use Benchmark qw( cmpthese );
use constant DAY => 60 * 60 * 24;

sub use_array {
  my @parts = localtime();
  $parts[3] -= 14;
  return POSIX::strftime('%Y%m%d', @parts);
}

sub use_math {
  return POSIX::strftime(
    '%Y%m%d',
    localtime(time - (14 * (60 * 60 * 24)))
  );
}

sub use_math_with_const {
  return POSIX::strftime('%Y%m%d', localtime(time - (14 * DAY )));
}

cmpthese(
  90000,
  {
    'use_array' => sub { use_array(); },
    'use_math' => sub { use_math(); },
    'use_math_with_const' => sub { use_math_with_const(); },
  },
);

__DATA__
Benchmark: timing 90000 iterations of use_array, use_math, use_math_with_const...
 use_array:  6 wallclock secs ( 5.67 usr +  0.10 sys =  5.77 CPU) @ 15597.92/s (n=90000)
  use_math:  4 wallclock secs ( 3.63 usr +  0.11 sys =  3.74 CPU) @ 24064.17/s (n=90000)
use_math_with_const:  3 wallclock secs ( 3.70 usr +  0.05 sys =  3.75 CPU) @ 24000.00/s (n=90000)
                       Rate       use_array use_math_with_const         use_math
use_array           15598/s              --                -35%             -35%
use_math_with_const 24000/s             54%                  --              -0%
use_math            24064/s             54%                  0%               --