use strict;
use warnings;
no warnings 'recursion';
use Benchmark 'cmpthese';
use List::Util 'shuffle';
my @work   = shuffle( 1 .. 2000, );
my @result = @work;

cmpthese(
    100,
    {   normal   => sub { @result = rec_max_normal(@work) },
        goto     => sub { @result = rec_max_goto(@work) },
        amp      => sub { @result = rec_max_amp(@work) },
        unrolled => sub { @result = rec_max_unrolled(@work) },
    }
);

sub rec_max_unrolled {
    {
        return () unless @_;
        my ( $h1, $h2 ) = ( shift, shift );
        if (@_) {
            unshift @_, ( $h1 > $h2 ) ? $h1 : $h2;
            redo;
        }
        elsif ( defined $h2 ) {
            return ( $h1 > $h2 ) ? $h1 : $h2;
        }
    }
}

sub rec_max_normal {
    {
        return () unless @_;
        my ( $h1, $h2 ) = ( shift, shift );
        if (@_) {
            unshift @_, ( $h1 > $h2 ) ? $h1 : $h2;
            rec_max_normal(@_);
        }
        elsif ( defined $h2 ) {
            return ( $h1 > $h2 ) ? $h1 : $h2;
        }
    }
}

sub rec_max_amp {
    {
        return () unless @_;
        my ( $h1, $h2 ) = ( shift, shift );
        if (@_) {
            unshift @_, ( $h1 > $h2 ) ? $h1 : $h2;
            &rec_max_amp;
        }
        elsif ( defined $h2 ) {
            return ( $h1 > $h2 ) ? $h1 : $h2;
        }
    }
}

sub rec_max_goto {
    {
        return () unless @_;
        my ( $h1, $h2 ) = ( shift, shift );
        if (@_) {
            unshift @_, ( $h1 > $h2 ) ? $h1 : $h2;
            goto &rec_max_goto;
        }
        elsif ( defined $h2 ) {
            return ( $h1 > $h2 ) ? $h1 : $h2;
        }
    }
}