Fix 23563: double unary- operator unstable for NANs

runtime/lib/double.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class _Double extends _Num implements double {
   factory _Double.fromInteger(int value)
       native "Double_doubleFromInteger";
 
   Type get runtimeType => double;
 
@@ skipping 29 matching lines @@
   double operator %(num other) {
     return _modulo(other.toDouble());
   }
   double _modulo(double other) native "Double_modulo";
 
   double remainder(num other) {
     return _remainder(other.toDouble());
   }
   double _remainder(double other) native "Double_remainder";
   double operator -() {
-    if (this == 0.0) {
-      // -0.0 is canonicalized by the VM's parser, therefore no cycles.
-      return isNegative ? 0.0 : -0.0;
-    }
-    return 0.0 - this;
+    // Handles properly 0.0, NAN, and other doubles.
+    return this._flipSignBit;

[srdjan, 2015/06/02 22:32:10]

Calling out to native should not be a performance problem as the optimized code
inlines double unary- to best assembly pattern.

   }
+  double get _flipSignBit native "Double_flipSignBit";
+
   bool operator ==(other) {
     if (!(other is num)) return false;
     return _equal(other.toDouble());
   }
   bool _equal(double other)native "Double_equal";
   bool _equalToInteger(int other) native "Double_equalToInteger";
   bool operator <(num other) {
     return other > this;
   }
   bool operator >(num other) {
@@ skipping 198 matching lines @@
         return EQUAL;
       }
     } else if (isNaN) {
       return other.isNaN ? EQUAL : GREATER;
     } else {
       // Other is NaN.
       return LESS;
     }
   }
 }