Fix Issue #427

Use Fastpath without random-call when only a single value is allowed to be returned.
Added test that result of Next() is within boundaries.

src/Numerics/Random/RandomSource.cs

@@ -472,6 +472,12 @@ namespace MathNet.Numerics.Random
         /// </summary>
         protected virtual long DoSampleInt64WithNBits(int bitCount)
         {
+			// Fast case: Only 0 is allowed to be returned
+            // No random call is needed
+            if (bitCount == 0)
+            {
+                return 0;
+            }
             var bytes = new byte[8];
             DoSampleBytes(bytes);
 
@@ -489,6 +495,13 @@ namespace MathNet.Numerics.Random
         /// <param name="maxExclusive">The exclusive upper bound of the random number returned.</param>
         protected virtual int DoSampleInteger(int maxExclusive)
         {
+			// Fast case: Only a single number is allowed to be returned
+            // No random call is needed
+            if (maxExclusive == 1)
+            {
+                return 0;
+            }
+			
             // non-biased implementation
             // (biased: return (int)(DoSample() * maxExclusive);)
 

src/UnitTests/Random/RandomTests.cs

@@ -78,6 +78,29 @@ namespace MathNet.Numerics.UnitTests.Random
             Assert.IsTrue(sum >= (N/2.0) - (.05*N));
             Assert.IsTrue(sum <= (N/2.0) + (.05*N));
 
+            var disposable = random as IDisposable;
+            if (disposable != null)
+            {
+                disposable.Dispose();
+            }
+        }
+		
+		/// <summary>
+        ///     Next() result is in boundaries.
+        /// </summary>
+        [Test]
+        public void Boundaries()
+        {
+            var random = (System.Random)Activator.CreateInstance(_randomType, new object[] { false });
+
+            for (var i = 1; i < N; i++)
+            {
+                var j = N;
+                var next = random.Next(i, j);
+                Assert.IsTrue(next >= i, string.Format("Value {0} is smaller than lower bound {1}", next, i));
+                Assert.IsTrue(next < j, string.Format("Value {0} is larger or equal to upper bound {1}", next, j));
+            }
+
             var disposable = random as IDisposable;
             if (disposable != null)
             {