BackpressureUtils capped add/multiply methods + tests

src/main/java/rx/internal/operators/BackpressureUtils.java

@@ -44,11 +44,7 @@ public static <T> long getAndAddRequest(AtomicLongFieldUpdater<T> requested, T o
         // add n to field but check for overflow
         while (true) {
             long current = requested.get(object);
-            long next = current + n;
-            // check for overflow
-            if (next < 0) {
-                next = Long.MAX_VALUE;
-            }
+            long next = addCap(current, n);
             if (requested.compareAndSet(object, current, next)) {
                 return current;
             }
@@ -70,14 +66,41 @@ public static long getAndAddRequest(AtomicLong requested, long n) {
         // add n to field but check for overflow
         while (true) {
             long current = requested.get();
-            long next = current + n;
-            // check for overflow
-            if (next < 0) {
-                next = Long.MAX_VALUE;
-            }
+            long next = addCap(current, n);
             if (requested.compareAndSet(current, next)) {
                 return current;
             }
         }
     }
+
+    /**
+     * Multiplies two positive longs and caps the result at Long.MAX_VALUE.
+     * @param a the first value
+     * @param b the second value
+     * @return the capped product of a and b
+     */
+    public static long multiplyCap(long a, long b) {
+        long u = a * b;
+        if (((a | b) >>> 31) != 0) {
+            if (b != 0L && (u / b != a)) {
+                u = Long.MAX_VALUE;
+            }
+        }
+        return u;
+    }
+
+    /**
+     * Adds two positive longs and caps the result at Long.MAX_VALUE.
+     * @param a the first value
+     * @param b the second value
+     * @return the capped sum of a and b
+     */
+    public static long addCap(long a, long b) {
+        long u = a + b;
+        if (u < 0L) {
+            u = Long.MAX_VALUE;
+        }
+        return u;
+    }
+
 }

src/test/java/rx/internal/operators/BackpressureUtilsTest.java

@@ -0,0 +1,39 @@
+/**
+ * Copyright 2015 Netflix, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package rx.internal.operators;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class BackpressureUtilsTest {
+    @Test
+    public void testAddCap() {
+        assertEquals(2L, BackpressureUtils.addCap(1, 1));
+        assertEquals(Long.MAX_VALUE, BackpressureUtils.addCap(1, Long.MAX_VALUE - 1));
+        assertEquals(Long.MAX_VALUE, BackpressureUtils.addCap(1, Long.MAX_VALUE));
+        assertEquals(Long.MAX_VALUE, BackpressureUtils.addCap(Long.MAX_VALUE - 1, Long.MAX_VALUE - 1));
+        assertEquals(Long.MAX_VALUE, BackpressureUtils.addCap(Long.MAX_VALUE, Long.MAX_VALUE));
+    }
+
+    @Test
+    public void testMultiplyCap() {
+        assertEquals(6, BackpressureUtils.multiplyCap(2, 3));
+        assertEquals(Long.MAX_VALUE, BackpressureUtils.multiplyCap(2, Long.MAX_VALUE));
+        assertEquals(Long.MAX_VALUE, BackpressureUtils.multiplyCap(Long.MAX_VALUE, Long.MAX_VALUE));
+        assertEquals(Long.MAX_VALUE, BackpressureUtils.multiplyCap(1L << 32, 1L << 32));
+
+    }
+}