implements HammingPeriodic and HanningPeriodic

src/FftSharp.Tests/WindowValueTests.cs

@@ -1,4 +1,4 @@
-using NUnit.Framework;
+using NUnit.Framework;
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -70,6 +70,15 @@ public void Test_Hamming()
             AssertEqual(Known_hamming_14, new Windows.Hamming().Create(14));
         }
 
+        [Test]
+        public void Test_HammingPeriodic()
+        {
+            double[] Known_hamming_periodic_13 = { 0.08, 0.13269023, 0.27869022, 0.48455313, 0.70311825, 0.88431494,0.98663324, 0.98663324, 0.88431494, 0.70311825, 0.48455313, 0.27869022, 0.13269023 };
+            double[] Known_hamming_periodic_14 = { 0.08, 0.12555432, 0.25319469, 0.43764037, 0.64235963, 0.82680531, 0.95444568, 1.0, 0.95444568, 0.82680531, 0.64235963, 0.43764037, 0.25319469, 0.12555432 };
+            AssertEqual(Known_hamming_periodic_13, new Windows.HammingPeriodic().Create(13));
+            AssertEqual(Known_hamming_periodic_14, new Windows.HammingPeriodic().Create(14));
+        }
+
         [Test]
         public void Test_Hanning()
         {
@@ -79,6 +88,15 @@ public void Test_Hanning()
             AssertEqual(Known_hanning_14, new Windows.Hanning().Create(14));
         }
 
+        [Test]
+        public void Test_HanningPeriodic()
+        {
+            double[] Known_hanning_periodic_13 = { 0.0, 0.05727199, 0.21596763, 0.43973166, 0.67730244, 0.87425537, 0.98547091, 0.98547091, 0.87425537, 0.67730244, 0.43973166, 0.21596763, 0.05727199 };
+            double[] Known_hanning_periodic_14 = { 0.0, 0.04951557, 0.1882551, 0.38873953, 0.61126047, 0.8117449, 0.95048443, 1.0, 0.95048443, 0.8117449, 0.61126047, 0.38873953, 0.1882551, 0.04951557 };
+            AssertEqual(Known_hanning_periodic_13, new Windows.HanningPeriodic().Create(13));
+            AssertEqual(Known_hanning_periodic_14, new Windows.HanningPeriodic().Create(14));
+        }
+
         [Test]
         public void Test_Rectangular()
         {

src/FftSharp/Windows/Hamming.cs

@@ -8,19 +8,22 @@ public class Hamming : Window, IWindow
         public override string Description =>
             "The Hamming window has a sinusoidal shape does NOT touch zero at the edges (unlike the similar Hanning window). " +
             "It is similar to the Hanning window but its abrupt edges are designed to cancel the largest side lobe. " +
-            "It may be a good choice for low-quality (8-bit) auto where side lobes lie beyond the quantization noise floor.";
+            "It may be a good choice for low-quality (8-bit) auto where side lobes lie beyond the quantization noise floor." +
+            "A symmetric window, for use in filter design.";
 
         public override double[] Create(int size, bool normalize = false)
         {
             double[] window = new double[size];
 
+            double phaseStep = (2.0 * Math.PI) / (size - 1.0);
+
             for (int i = 0; i < size; i++)
-                window[i] = 0.54 - 0.46 * Math.Cos(2 * Math.PI * i / (size - 1));
+                window[i] = 0.54 - 0.46 * Math.Cos(i * phaseStep);
 
             if (normalize)
                 NormalizeInPlace(window);
 
             return window;
         }
     }
-}
+}

src/FftSharp/Windows/HammingPeriodic.cs

@@ -0,0 +1,29 @@
+using System;
+
+namespace FftSharp.Windows
+{
+    public class HammingPeriodic : Window, IWindow
+    {
+        public override string Name => "HammingPeriodic";
+        public override string Description =>
+            "The Hamming window has a sinusoidal shape does NOT touch zero at the edges (unlike the similar Hanning window). " +
+            "It is similar to the Hanning window but its abrupt edges are designed to cancel the largest side lobe. " +
+            "It may be a good choice for low-quality (8-bit) auto where side lobes lie beyond the quantization noise floor." +
+            "A periodic window, for use in spectral analysis.";
+
+        public override double[] Create(int size, bool normalize = false)
+        {
+            double[] window = new double[size];
+
+            double phaseStep = (2.0 * Math.PI) / size;
+
+            for (int i = 0; i < size; i++)
+                window[i] = 0.54 - 0.46 * Math.Cos(i * phaseStep);
+
+            if (normalize)
+                NormalizeInPlace(window);
+
+            return window;
+        }
+    }
+}

src/FftSharp/Windows/Hanning.cs

@@ -8,14 +8,17 @@ public class Hanning : Window, IWindow
         public override string Description =>
             "The Hanning window has a sinusoidal shape which touches zero at the edges (unlike the similar Hamming window). " +
             "It has good frequency resolution, low spectral leakage, and is satisfactory for 95 percent of use cases. " +
-            "If you do not know the nature of the signal but you want to apply a smoothing window, start with the Hann window.";
+            "If you do not know the nature of the signal but you want to apply a smoothing window, start with the Hann window." +
+            "A symmetric window, for use in filter design.";
 
         public override double[] Create(int size, bool normalize = false)
         {
             double[] window = new double[size];
 
+            double phaseStep = (2.0 * Math.PI) / (size - 1.0);
+
             for (int i = 0; i < size; i++)
-                window[i] = 0.5 - 0.5 * Math.Cos(2 * Math.PI * i / (size - 1));
+                window[i] = 0.5 - 0.5 * Math.Cos(i * phaseStep);
 
             if (normalize)
                 NormalizeInPlace(window);

src/FftSharp/Windows/HanningPeriodic.cs

@@ -0,0 +1,29 @@
+using System;
+
+namespace FftSharp.Windows
+{
+    public class HanningPeriodic : Window, IWindow
+    {
+        public override string Name => "HanningPeriodic";
+        public override string Description =>
+            "The Hanning window has a sinusoidal shape which touches zero at the edges (unlike the similar Hamming window). " +
+            "It has good frequency resolution, low spectral leakage, and is satisfactory for 95 percent of use cases. " +
+            "If you do not know the nature of the signal but you want to apply a smoothing window, start with the Hann window." +
+            "A periodic window, for use in spectral analysis.";
+
+        public override double[] Create(int size, bool normalize = false)
+        {
+            double[] window = new double[size];
+
+            double phaseStep = (2.0 * Math.PI) / size;
+
+            for (int i = 0; i < size; i++)
+                window[i] = 0.5 - 0.5 * Math.Cos(i * phaseStep);
+
+            if (normalize)
+                NormalizeInPlace(window);
+
+            return window;
+        }
+    }
+}