To make it extremely simple, consider the code:

At last, a technical argument. For safety.

This

sub odd {
    die 'Out of integer range' 
        if $_[ 0 ] & 0xffffffff != $_[ 0 ]; ## Should be done by perl!
    return $_[ 0 ] & 1;
}
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Versus this

sub odd {
    my $num= shift @ARGV;
    die 'Number too big to test for oddness'
        if $num > 9_007_199_254_740__992;

    die 'Number too small to test for oddness' 
        if $num < -9_007_199_254_740__992;

    die 'Cannot test #INFinity for oddness'
        if $num eq '1.#INF';

    die 'Cannot test negative #INFinity for oddness'
        if $num eq '-1.#INF';

    die 'Cannot test #IND for oddness'
        if $num eq '1.#IND';

    die 'Cannot test negative #IND for oddness'
        if $num eq '-1.#IND';

    die 'Cannot test a non number for oddness'
        if $num eq '1.#QNAN;

    die 'Cannot test negative non number for oddness'
        if $num eq '-1.#QNAN;

    die 'Cannot test a non-integer for oddness'  
        if int( $num ) != $num;

    return $num % 2 ? 1 : 0;
}
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