my $fmt= "LIJ";
while(  1  ) {
    last
        if  length( pack substr($fmt,0,1), 0 ) == length( pack "p", "" );
    $fmt= substr( $fmt, 1 );
    die "No unpack format for integers the same size as pointers"
        if  ! $fmt;
}
$fmt= substr( $fmt, 0, 1 );

my $addr= unpack $fmt, pack "p", $string;