Fixed infinite loop in FastMath.pow(double, long) with Long.MIN_VALUE.

JIRA: MATH-1272

src/changes/changes.xml

@@ -54,6 +54,9 @@ If the output is not quite correct, check for invisible trailing spaces!
     </release>
 
     <release version="4.0" date="XXXX-XX-XX" description="">
+      <action dev="luc" type="fix" issue="MATH-1272" due-to="Qualtagh">
+        Fixed infinite loop in FastMath.pow(double, long) with Long.MIN_VALUE.
+      </action>
       <action dev="luc" type="fix" issue="MATH-1266"> <!-- backported to 3.6 -->
         Fixed split/side inconsistencies in BSP trees.
       </action>

src/main/java/org/apache/commons/math4/util/FastMath.java

@@ -1711,7 +1711,7 @@ public class FastMath {
         }
 
         /** Computes this^e.
-         * @param e exponent (beware, here it MUST be > 0)
+         * @param e exponent (beware, here it MUST be > 0; the only exclusion is Long.MIN_VALUE)
          * @return d^e, split in high and low bits
          * @since 4.0
          */
@@ -1723,7 +1723,7 @@ public class FastMath {
             // d^(2p)
             Split d2p = new Split(full, high, low);
 
-            for (long p = e; p != 0; p >>= 1) {
+            for (long p = e; p != 0; p >>>= 1) {
 
                 if ((p & 0x1) != 0) {
                     // accurate multiplication result = result * d^(2p) using Veltkamp TwoProduct algorithm

src/test/java/org/apache/commons/math4/util/FastMathTest.java

@@ -1232,6 +1232,11 @@ public class FastMathTest {
         Assert.assertTrue(Double.isInfinite(FastMath.pow(FastMath.scalb(1.0, 500), 4)));
     }
 
+    @Test(timeout=5000L) // This test must finish in finite time.
+    public void testIntPowLongMinValue() {
+        Assert.assertEquals(1.0, FastMath.pow(1.0, Long.MIN_VALUE), -1.0);
+    }
+
     @Test
     public void testIncrementExactInt() {
         int[] specialValues = new int[] {