Simplified huffman encoding via compiled tree

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src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanLut.cs

@@ -5,8 +5,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
 {
     /// <summary>
     /// A compiled look-up table representation of a huffmanSpec.
-    /// Each value maps to a uint32 of which the 8 most significant bits hold the
-    /// codeword size in bits and the 24 least significant bits hold the codeword.
+    /// Each value maps to a int32 of which the 24 most significant bits hold the
+    /// codeword in bits and the 8 least significant bits hold the codeword size.
     /// The maximum codeword size is 16 bits.
     /// </summary>
     internal readonly struct HuffmanLut
@@ -51,10 +51,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
 
             for (int i = 0; i < spec.Count.Length; i++)
             {
-                int bits = (i + 1) << 24;
+                int len = i + 1;
                 for (int j = 0; j < spec.Count[i]; j++)
                 {
-                    this.Values[spec.Values[k]] = bits | code;
+                    this.Values[spec.Values[k]] = len | (code << 8);
                     code++;
                     k++;
                 }

src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanScanEncoder.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.IO;
 using System.Linq;
 using System.Runtime.CompilerServices;
@@ -354,7 +355,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
         private void EmitHuff(int[] table, int value)
         {
             int x = table[value];
-            this.Emit(x & ((1 << 24) - 1), x >> 24);
+            this.Emit(x >> 8, x & 0xff);
         }
 
         /// <summary>

src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanSpec.cs

@@ -24,9 +24,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
                             0, 0, 0
                         },
                     new byte[]
-                            {
-                               0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
-                            }),
+                        {
+                            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
+                        }),
 
                 // Luminance AC.
                 new HuffmanSpec(