Rational#==

static VALUE
nurat_eqeq_p(VALUE self, VALUE other)
{
    if (RB_INTEGER_TYPE_P(other)) {
        get_dat1(self);

        if (RB_INTEGER_TYPE_P(dat->num) && RB_INTEGER_TYPE_P(dat->den)) {
            if (INT_ZERO_P(dat->num) && INT_ZERO_P(other))
                return Qtrue;

            if (!FIXNUM_P(dat->den))
                return Qfalse;
            if (FIX2LONG(dat->den) != 1)
                return Qfalse;
            return rb_int_equal(dat->num, other);
        }
        else {
            const double d = nurat_to_double(self);
            return f_boolcast(FIXNUM_ZERO_P(rb_dbl_cmp(d, NUM2DBL(other))));
        }
    }
    else if (RB_FLOAT_TYPE_P(other)) {
        const double d = nurat_to_double(self);
        return f_boolcast(FIXNUM_ZERO_P(rb_dbl_cmp(d, RFLOAT_VALUE(other))));
    }
    else if (RB_TYPE_P(other, T_RATIONAL)) {
        {
            get_dat2(self, other);

            if (INT_ZERO_P(adat->num) && INT_ZERO_P(bdat->num))
                return Qtrue;

            return f_boolcast(rb_int_equal(adat->num, bdat->num) &&
                              rb_int_equal(adat->den, bdat->den));
        }
    }
    else {
        return rb_equal(other, self);
    }
}