MATH-1047

Added overflow checking to "ArithmeticUtils.pow(long,int)".


git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1537324 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/commons/math3/util/ArithmeticUtils.java

@@ -706,25 +706,45 @@ public final class ArithmeticUtils {
      *
      * @param k Number to raise.
      * @param e Exponent (must be positive or zero).
-     * @return k<sup>e</sup>
+     * @return \( k^e \)
      * @throws NotPositiveException if {@code e < 0}.
+     * @throws MathArithmeticException if the result would overflow.
      */
-    public static long pow(final long k, int e) throws NotPositiveException {
+    public static long pow(final long k,
+                           final int e)
+        throws NotPositiveException,
+               MathArithmeticException {
         if (e < 0) {
             throw new NotPositiveException(LocalizedFormats.EXPONENT, e);
         }
 
-        long result = 1l;
-        long k2p    = k;
-        while (e != 0) {
-            if ((e & 0x1) != 0) {
-                result *= k2p;
-            }
-            k2p *= k2p;
-            e = e >> 1;
-        }
+        try {
+            int exp = e;
+            long result = 1;
+            long k2p    = k;
+            while (true) {
+                if ((exp & 0x1) != 0) {
+                    result = mulAndCheck(result, k2p);
+                }
 
-        return result;
+                exp >>= 1;
+                if (exp == 0) {
+                    break;
+                }
+
+                k2p = mulAndCheck(k2p, k2p);
+            }
+
+            return result;
+        } catch (MathArithmeticException mae) {
+            // Add context information.
+            mae.getContext().addMessage(LocalizedFormats.OVERFLOW);
+            mae.getContext().addMessage(LocalizedFormats.BASE, k);
+            mae.getContext().addMessage(LocalizedFormats.EXPONENT, e);
+
+            // Rethrow.
+            throw mae;
+        }
     }
 
     /**

src/test/java/org/apache/commons/math3/util/ArithmeticUtilsTest.java

@@ -461,29 +461,33 @@ public class ArithmeticUtilsTest {
     }
 
     @Test(expected=MathArithmeticException.class)
-    public void testPowIntIntOverflow() {
-        final int base = 21;
-        final int exp = 8;
-        ArithmeticUtils.pow(base, exp);
+    public void testPowIntOverflow() {
+        ArithmeticUtils.pow(21, 8);
     }
+
     @Test
-    public void testPowIntIntNoOverflow() {
+    public void testPowInt() {
         final int base = 21;
-        final int exp = 7;
-        ArithmeticUtils.pow(base, exp);
+
+        Assert.assertEquals(85766121L,
+                            ArithmeticUtils.pow(base, 6));
+        Assert.assertEquals(1801088541L,
+                            ArithmeticUtils.pow(base, 7));
     }
 
     @Test(expected=MathArithmeticException.class)
-    public void testPowNegativeIntIntOverflow() {
-        final int base = -21;
-        final int exp = 8;
-        ArithmeticUtils.pow(base, exp);
+    public void testPowNegativeIntOverflow() {
+        ArithmeticUtils.pow(-21, 8);
     }
+
     @Test
-    public void testPowNegativeIntIntNoOverflow() {
+    public void testPowNegativeInt() {
         final int base = -21;
-        final int exp = 7;
-        ArithmeticUtils.pow(base, exp);
+
+        Assert.assertEquals(85766121,
+                            ArithmeticUtils.pow(base, 6));
+        Assert.assertEquals(-1801088541,
+                            ArithmeticUtils.pow(base, 7));
     }
 
     @Test
@@ -504,6 +508,54 @@ public class ArithmeticUtilsTest {
         }
     }
 
+    @Test(expected=MathArithmeticException.class)
+    public void testPowLongOverflow() {
+        ArithmeticUtils.pow(21, 15);
+    }
+
+    @Test
+    public void testPowLong() {
+        final long base = 21;
+
+        Assert.assertEquals(154472377739119461L,
+                            ArithmeticUtils.pow(base, 13));
+        Assert.assertEquals(3243919932521508681L,
+                            ArithmeticUtils.pow(base, 14));
+    }
+
+    @Test(expected=MathArithmeticException.class)
+    public void testPowNegativeLongOverflow() {
+        ArithmeticUtils.pow(-21L, 15);
+    }
+
+    @Test
+    public void testPowNegativeLong() {
+        final long base = -21;
+
+        Assert.assertEquals(-154472377739119461L,
+                            ArithmeticUtils.pow(base, 13));
+        Assert.assertEquals(3243919932521508681L,
+                            ArithmeticUtils.pow(base, 14));
+    }
+
+    @Test
+    public void testPowMinusOneLong() {
+        final long base = -1;
+        for (int i = 0; i < 100; i++) {
+            final long pow = ArithmeticUtils.pow(base, i);
+            Assert.assertEquals("i: " + i, i % 2 == 0 ? 1 : -1, pow);
+        }
+    }
+
+    @Test
+    public void testPowOneLong() {
+        final long base = 1;
+        for (int i = 0; i < 100; i++) {
+            final long pow = ArithmeticUtils.pow(base, i);
+            Assert.assertEquals("i: " + i, 1, pow);
+        }
+    }
+
     @Test
     public void testIsPowerOfTwo() {
         final int n = 1025;