sub setbit {
    # args:  var, offset, value (0/1)
    if ($_[1] % 2) {                          # odd offset
        if ($_[2]) {
            vec($_[0], $_[1]/2, 2) |= 0b10;     # set
        } else {
            vec($_[0], $_[1]/2, 2) &= 1;        # clear
        }
    } else {                                  # even offset
        if ($_[2]) {
            vec($_[0], $_[1]/2, 2) |= 1;        # set
        } else {
            vec($_[0], $_[1]/2, 2) &= 0b10;     # clear
        }
    }
}

my $v = "";
setbit($v, 2**32-1, 1);  # set bit
setbit($v, 2**32-1, 0);  # clear bit