#!/usr/local/bin/perl -w

use strict;
use Benchmark;

my $i = 0;

timethese(200000, {
 RAND_AND=>\&and_rand,
 RAND_MOD=>\&mod_rand,
 TWO_AND=>\&two_and,
 TWO_MOD=>\&two_mod,
});

sub and_rand {
  my $num = rand(2**31);
  return $num & 1;
}

sub mod_rand {
  my $num = rand(2**31);
  return $num % 2;
}

sub two_mod {
 $i++ % 2;
}

sub two_and {
 $i++ & 1;
}
~
"tst" 31 lines, 359 characters 
~/tst>./tst
Benchmark: timing 200000 iterations of RAND_AND, RAND_MOD, TWO_AND, TWO_MOD...
  RAND_AND:  1 wallclock secs ( 1.12 usr +  0.00 sys =  1.12 CPU) @ 178571.43/s (n=200000)
  RAND_MOD:  0 wallclock secs ( 1.10 usr +  0.00 sys =  1.10 CPU) @ 181818.18/s (n=200000)
   TWO_AND:  0 wallclock secs ( 0.36 usr + -0.01 sys =  0.35 CPU) @ 571428.57/s (n=200000)
            (warning: too few iterations for a reliable count)
   TWO_MOD:  2 wallclock secs ( 0.42 usr + -0.00 sys =  0.42 CPU) @ 476190.48/s (n=200000)
~/tst>