Fix int.compareTo.

runtime/lib/integers.dart

Index: runtime/lib/integers.dart
diff --git a/runtime/lib/integers.dart b/runtime/lib/integers.dart
index c1a79c8f843e7f9a4c9e596090f43dd603d19196..f2eaf9f645c762cfb51bac88c99937c5e2cf486e 100644
--- a/runtime/lib/integers.dart
+++ b/runtime/lib/integers.dart
@@ -97,15 +97,16 @@ class IntegerImplementation {
 
   int compareTo(Comparable other) {

[Lasse Reichstein Nielsen, 2012/07/06 08:56:17]

Argh. Why did we not define Comparable to be generic, so num is Comparable<num>?
We only ever want to receive num values here. Later we do "this < other" and
int.operator< will/should throw on any non-num.
I think you should change the parameter to "num other". It's a valid subtype of
(Comparable)->int.

[floitsch, 2012/07/06 13:18:55]

Changing to num now, and adding generic type to comparable in a separate CL.

     final int EQUAL = 0, LESS = -1, GREATER = 1;
+    if (other is double) {
+      // Let the double implementation deal with -0.0 and NaN.
+      return -other.compareTo(this.toDouble());

[Lasse Reichstein Nielsen, 2012/07/06 08:56:17]

I think that's wrong.
If this is, e.g., 1<<2000 (an int) this will make it compare equal to Infinity,
and so will 1<<2001, but those two are not equal, breaking transitivity.
Ditto for this being 1<<55+1 vs 1<<55+2 and the double 2^55.

I.e., only convert blindly to double if this is in the range 
[-2^53..2^53]. Above that, you lose precission.
That's also the range where doubles can have decimals, so outside that range,
you can convert the double to an int instead, but you have to rule out
Infinities/NaN first.

I.e., if other is a double, do:
  const MAX_EXACT_INT_TO_DOUBLE = ... value of 2^53 ...;
  const MIN_EXACT_INT_TO_DOUBLE = -MAX_EXACT_INT_TO_DOUBLE;
  double d = other;
  if (!d.isFinite()) {
    return d == double.NEGATIVE_INFINITY ? GREATER : LESS;
  }
  if (MIN_EXACT_INT_TO_DOUBLE <= this && 
      this <= MAX_EXACT_INT_TO_DOUBLE) {
    return -d.compareTo(this.toDouble());
  } else {
    // If abs(other) > MAX_EXACT_DOUBLE, then other has 
    // an integer value (no bits below the decimal point).
    other = d.toInt();
  }

[floitsch, 2012/07/06 13:18:55]

Done.

+    }
     if (this < other) {
       return LESS;
     } else if (this > other) {
       return GREATER;
-    } else if (this == other) {
-      return EQUAL;
     } else {
-      // Other is NaN.
-      return LESS;
+      return EQUAL;
     }
   }