--- old/src/share/classes/java/util/stream/ReduceOps.java	2013-11-19 11:34:21.000000000 -0800
+++ new/src/share/classes/java/util/stream/ReduceOps.java	2013-11-19 11:34:21.000000000 -0800
@@ -599,6 +599,62 @@
     }
 
     /**
+     * Constructs a {@code TerminalOp} that implements a functional reduce on
+     * {@code double} values.
+     *
+     * @param identity the identity for the combining function
+     * @param operator the combining function
+     * @return a {@code TerminalOp} implementing the reduction
+     */
+    public static TerminalOp<Double, Double>
+    makeDoubleCompensatingSummer() {
+        class ReducingSink
+                implements AccumulatingSink<Double, Double, ReducingSink>, Sink.OfDouble {
+            private double sum;
+            private double sumCompensation;
+
+            /**
+             * Incorporate a new double value using Kahan summation /
+             * compensation summation.
+             */
+            private void sumWithCompensation(double value) {
+                double tmp = value - sumCompensation;
+                double velvel = sum + tmp; // Little wolf of rounding error
+                sumCompensation = (velvel - sum) - tmp;
+                sum = velvel;
+            }
+
+            @Override
+            public void begin(long size) {
+                sum = 0.0;
+                sumCompensation = 0.0;
+            }
+
+            @Override
+            public void accept(double t) {
+                sumWithCompensation(t);
+            }
+
+            @Override
+            public Double get() {
+                return sum;
+            }
+
+            @Override
+            public void combine(ReducingSink other) {
+                accept(other.sum);
+                accept(other.sumCompensation);
+            }
+        }
+        return new ReduceOp<Double, Double, ReducingSink>(StreamShape.DOUBLE_VALUE) {
+            @Override
+            public ReducingSink makeSink() {
+                return new ReducingSink();
+            }
+        };
+    }
+
+    /**
      * Constructs a {@code TerminalOp} that implements a mutable reduce on
      * {@code double} values.
      *