Added Log2 tests

tests/ImageSharp.Tests/Common/NumericsTests.cs

@@ -0,0 +1,73 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace SixLabors.ImageSharp.Tests.Common
+{
+    public class NumericsTests
+    {
+        private ITestOutputHelper Output { get; }
+
+        public NumericsTests(ITestOutputHelper output)
+        {
+            this.Output = output;
+        }
+
+        private static int Log2_ReferenceImplementation(uint value)
+        {
+            int n = 0;
+            while ((value >>= 1) != 0)
+            {
+                ++n;
+            }
+
+            return n;
+        }
+
+        [Fact]
+        public void Log2_ZeroConvention()
+        {
+            uint value = 0;
+            int expected = 0;
+            int actual = Numerics.Log2(value);
+
+            Assert.True(expected == actual, $"Expected: {expected}, Actual: {actual}");
+        }
+
+        [Fact]
+        public void Log2_PowersOfTwo()
+        {
+            for (int i = 0; i < sizeof(int) * 8; i++)
+            {
+                // from 2^0 to 2^32
+                uint value = (uint)(1 << i);
+                int expected = i;
+                int actual = Numerics.Log2(value);
+
+                Assert.True(expected == actual, $"Expected: {expected}, Actual: {actual}");
+            }
+        }
+
+        [Theory]
+        [InlineData(1, 100)]
+        [InlineData(2, 100)]
+        public void Log2_RandomValues(int seed, int count)
+        {
+            var rng = new Random(seed);
+            byte[] bytes = new byte[4];
+
+            for (int i = 0; i < count; i++)
+            {
+                rng.NextBytes(bytes);
+                uint value = BitConverter.ToUInt32(bytes, 0);
+                int expected = Log2_ReferenceImplementation(value);
+                int actual = Numerics.Log2(value);
+
+                Assert.True(expected == actual, $"Expected: {expected}, Actual: {actual}");
+            }
+        }
+    }
+}