Added tests for GetHuffmanEncodingLength

tests/ImageSharp.Tests/Formats/Jpg/HuffmanScanEncoderTests.cs

@@ -0,0 +1,88 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+#if SUPPORTS_RUNTIME_INTRINSICS
+using System.Runtime.Intrinsics.X86;
+#endif
+using SixLabors.ImageSharp.Formats.Jpeg.Components;
+using SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder;
+using SixLabors.ImageSharp.Tests.Formats.Jpg.Utils;
+using SixLabors.ImageSharp.Tests.TestUtilities;
+using Xunit;
+using Xunit.Abstractions;
+
+// ReSharper disable InconsistentNaming
+namespace SixLabors.ImageSharp.Tests.Formats.Jpg
+{
+    [Trait("Format", "Jpg")]
+    public class HuffmanScanEncoderTests
+    {
+        private ITestOutputHelper Output { get; }
+
+        public HuffmanScanEncoderTests(ITestOutputHelper output)
+        {
+            Output = output;
+        }
+
+        private static int GetHuffmanEncodingLength_Reference(uint number)
+        {
+            int bits = 0;
+            if (number > 32767)
+            {
+                number >>= 16;
+                bits += 16;
+            }
+            if (number > 127)
+            {
+                number >>= 8;
+                bits += 8;
+            }
+            if (number > 7)
+            {
+                number >>= 4;
+                bits += 4;
+            }
+            if (number > 1)
+            {
+                number >>= 2;
+                bits += 2;
+            }
+            if (number > 0)
+            {
+                bits++;
+            }
+            return bits;
+        }
+
+        [Fact]
+        public void GetHuffmanEncodingLength_Zero()
+        {
+            int expected = 0;
+
+            int actual = HuffmanScanEncoder.GetHuffmanEncodingLength(0);
+
+            Assert.Equal(expected, actual);
+        }
+
+        [Theory]
+        [InlineData(1)]
+        [InlineData(2)]
+        public void GetHuffmanEncodingLength_Random(int seed)
+        {
+            int maxNumber = 1 << 16;
+
+            var rng = new Random(seed);
+            for (int i = 0; i < 1000; i++)
+            {
+                uint number = (uint)rng.Next(0, maxNumber);
+
+                int expected = GetHuffmanEncodingLength_Reference(number);
+
+                int actual = HuffmanScanEncoder.GetHuffmanEncodingLength(number);
+
+                Assert.Equal(expected, actual);
+            }
+        }
+    }
+}