preliminary work to get both Rat and FatRat working

Fails just one test that does (2/3) but SomeRole

src/core/Rat.pm

@@ -1,5 +1,7 @@
-# XXX: should also be Cool, but attributes and MI don't seem to mix yet
-my class Rat is Real {
+my Int $UINT64_UPPER = nqp::pow_I(2, 64, Num, Int);
+subset UInt64 of Int where { 0 <= $_ < $UINT64_UPPER } 
+
+my role Rational is Real {
     has Int $.numerator;
     has Int $.denominator;
 
@@ -55,6 +57,31 @@ my class Rat is Real {
     }
 }
 
+# XXX: should also be Cool
+my class Rat does Rational { }
+my class FatRat does Rational { }
+
+sub DIVIDE_NUMBERS(Int:D \$nu, Int:D \$de, $t1, $t2) {
+    my Int $gcd        := $nu gcd $de;
+    my Int $numerator   = $nu div $gcd;
+    my Int $denominator = $de div $gcd;
+    if $denominator < 0 {
+        $numerator   = -$numerator;
+        $denominator = -$denominator;
+    }
+    if nqp::istype($nu, FatRat) || nqp::istype($de, FatRat) {
+        my $r := nqp::create(FatRat);
+        nqp::bindattr($r, FatRat, '$!numerator',   nqp::p6decont($numerator));
+        nqp::bindattr($r, FatRat, '$!denominator', nqp::p6decont($denominator));
+    } elsif $denominator <= $UINT64_UPPER {
+        my $r := nqp::create(Rat);
+        nqp::bindattr($r, Rat, '$!numerator',   nqp::p6decont($numerator));
+        nqp::bindattr($r, Rat, '$!denominator', nqp::p6decont($denominator));
+    } else {
+
+    }
+}
+
 multi prefix:<->(Rat \$a) {
     Rat.new(-$a.numerator, $a.denominator);
 }