String#bitwise_not

static VALUE
rb_str_bitwise_not(VALUE str)
{
    rb_len_t len = RSTRING_LEN(str);
    VALUE result = str_bitwise_result(str);
    str_bitwise_not((unsigned char *)RSTRING_PTR(result),
                    (const unsigned char *)RSTRING_PTR(str), len);
    return result;
}