There is no magic to sprinkle over an algorithm that relies on 32-bit integers to make it behave with other integer sizes. The hardcoded numbers here are magic for 32-bit numbers:

    $num = $num - 4294967296 if $num > 4294967295;
    $num = $num + 4294967296 if $num < -2147483648;
[download]

You will have to understand the algorithm involved to be able to make the required changes. Alternatively, you can run the program under a Perl compiled with 32-bit integers.

Try this -- 'scuse the formatting, but there's no good way to format it. It produces the same results on 32-bit and 64-bit Perls for one randomly generated set of input data:

for( my $h = 16; $h < 80; $h++ ) {
    $i[$h] = a2(
        (
            (
                (
                    (
                        ( $i[$h - 3] ^ $i[$h - 8] ) & 0xffffffff
                    ) ^ $i[$h - 14]
                ) & 0xffffffff
            ) ^ $i[$h - 16]
        ) & 0xffffffff
    , 1
    );
}

print "@i";

sub a2 {
    my ($b, $a) = @_;

    my $c = $b >> 32 - $a;
    my $e = (1 << 32 - $a) - 1;
    my $d = $b & $e;

    return tos($d << $a | $c);
}

sub tos {
    my ($num) = @_;
    $num = $num - 4294967296 if $num > 4294967295;
    $num = $num + 4294967296 if $num < -2147483648;

    if ($num >= 0) {
        $num = $num - 2 ** 32 if ($num >> 31);
    }
    return $num;
}
[download]

This is slightly more readable:

sub fix32{ $_[0] & 0xffffffff }

for( my $h = 16; $h < 80; $h++ ) {
    $i[$h] = a2(
        fix32( fix32( fix32( $i[$h - 3] ^ $i[$h - 8] ) ^ $i[$h - 14] )
+ ^ $i[$h - 16] )
        , 1
    );
}
[download]