number theory: integer IsPowerOfTwo

Signed-off-by: Christoph Ruegg <git@cdrnet.ch>

src/Managed.UnitTests/NumberTheoryTests/IntegerTheoryTest.cs

@@ -73,6 +73,64 @@ namespace MathNet.Numerics.UnitTests.NumberTheoryTests
             Assert.IsFalse(IntegerTheory.IsOdd(Int64.MinValue), "Int64.Min is not odd");
         }
 
+        [Test]
+        public void TestIsPowerOfTwo32()
+        {
+            for (int i = 2; i < 31; i++)
+            {
+                int x = 1 << i;
+                Assert.IsTrue(IntegerTheory.IsPowerOfTwo(x), x + " (+)");
+                Assert.IsFalse(IntegerTheory.IsPowerOfTwo(x - 1), x + "-1 (-)");
+                Assert.IsFalse(IntegerTheory.IsPowerOfTwo(x + 1), x + "+1 (-)");
+                Assert.IsFalse(IntegerTheory.IsPowerOfTwo(-x), "-" + x + " (-)");
+                Assert.IsFalse(IntegerTheory.IsPowerOfTwo(-x + 1), "-" + x + "+1 (-)");
+                Assert.IsFalse(IntegerTheory.IsPowerOfTwo(-x - 1), "-" + x + "-1 (-)");
+            }
+
+            Assert.IsTrue(IntegerTheory.IsPowerOfTwo(4), "4 (+)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(3), "3 (-)");
+            Assert.IsTrue(IntegerTheory.IsPowerOfTwo(2), "2 (+)");
+            Assert.IsTrue(IntegerTheory.IsPowerOfTwo(1), "1 (+)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(0), "0 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(-1), "-1 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(-2), "-2 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(-3), "-3 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(-4), "-4 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(Int32.MinValue), "Int32.MinValue (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(Int32.MinValue+1), "Int32.MinValue+1 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(Int32.MaxValue), "Int32.MaxValue (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(Int32.MaxValue-1), "Int32.MaxValue-1 (-)");
+        }
+
+        [Test]
+        public void TestIsPowerOfTwo64()
+        {
+            for (int i = 2; i < 63; i++)
+            {
+                long x = ((long)1) << i;
+                Assert.IsTrue(IntegerTheory.IsPowerOfTwo(x), x + " (+)");
+                Assert.IsFalse(IntegerTheory.IsPowerOfTwo(x - 1), x + "-1 (-)");
+                Assert.IsFalse(IntegerTheory.IsPowerOfTwo(x + 1), x + "+1 (-)");
+                Assert.IsFalse(IntegerTheory.IsPowerOfTwo(-x), "-" + x + " (-)");
+                Assert.IsFalse(IntegerTheory.IsPowerOfTwo(-x + 1), "-" + x + "+1 (-)");
+                Assert.IsFalse(IntegerTheory.IsPowerOfTwo(-x - 1), "-" + x + "-1 (-)");
+            }
+
+            Assert.IsTrue(IntegerTheory.IsPowerOfTwo((long)4), "4 (+)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo((long)3), "3 (-)");
+            Assert.IsTrue(IntegerTheory.IsPowerOfTwo((long)2), "2 (+)");
+            Assert.IsTrue(IntegerTheory.IsPowerOfTwo((long)1), "1 (+)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo((long)0), "0 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo((long)-1), "-1 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo((long)-2), "-2 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo((long)-3), "-3 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo((long)-4), "-4 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(Int64.MinValue), "Int32.MinValue (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(Int64.MinValue+1), "Int32.MinValue+1 (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(Int64.MaxValue), "Int32.MaxValue (-)");
+            Assert.IsFalse(IntegerTheory.IsPowerOfTwo(Int64.MaxValue-1), "Int32.MaxValue-1 (-)");
+        }
+
         [Test]
         public void TestIsPerfectSquare32()
         {

src/Managed/NumberTheory/IntegerTheory.cs

@@ -75,6 +75,26 @@ namespace MathNet.Numerics.NumberTheory
             return (number & 0x1) == 0x1;
         }
 
+        /// <summary>
+        /// Find out whether the provided 32 bit integer is a perfect power of two.
+        /// </summary>
+        /// <param name="number">The number to very whether it's a power of two.</param>
+        /// <returns>True if and only if it is a power of two.</returns>
+        public static bool IsPowerOfTwo(this int number)
+        {
+            return number > 0 && (number & (number - 1)) == 0x0;
+        }
+
+        /// <summary>
+        /// Find out whether the provided 64 bit integer is a perfect power of two.
+        /// </summary>
+        /// <param name="number">The number to very whether it's a power of two.</param>
+        /// <returns>True if and only if it is a power of two.</returns>
+        public static bool IsPowerOfTwo(this long number)
+        {
+            return number > 0 && (number & (number - 1)) == 0x0;
+        }
+
         /// <summary>
         /// Find out whether the provided 32 bit integer is a perfect square, i.e. a square of an integer.
         /// </summary>