Rational#rationalize

static VALUE
nurat_rationalize(int argc, VALUE *argv, VALUE self)
{
    VALUE e, a, b, p, q;
    VALUE rat = self;
    get_dat1(self);

    if (rb_check_arity(argc, 0, 1) == 0)
        return self;

    e = f_abs(argv[0]);

    if (INT_NEGATIVE_P(dat->num)) {
        rat = f_rational_new2(RBASIC_CLASS(self), rb_int_uminus(dat->num), dat->den);
    }

    a = FIXNUM_ZERO_P(e) ? rat : rb_rational_minus(rat, e);
    b = FIXNUM_ZERO_P(e) ? rat : rb_rational_plus(rat, e);

    if (f_eqeq_p(a, b))
        return self;

    nurat_rationalize_internal(a, b, &p, &q);
    if (rat != self) {
        RATIONAL_SET_NUM(rat, rb_int_uminus(p));
        RATIONAL_SET_DEN(rat, q);
        return rat;
    }
    return f_rational_new2(CLASS_OF(self), p, q);
}