Add TOC encoder

src/ImageSharp/Formats/Jxl/Processing/Encoder/JxlCoefficientOrderEncoder.cs

@@ -313,7 +313,7 @@ internal static class JxlCoefficientOrderEncoder
         return true;
     }
 
-    private static bool EncodePermutation(ReadOnlySpan<uint> order, int skip, int size, JxlBitWriter writer)
+    public static bool EncodePermutation(ReadOnlySpan<uint> order, int skip, int size, JxlBitWriter writer)
     {
         List<JxlToken>[] tokens = [[]];
 

src/ImageSharp/Formats/Jxl/Processing/Encoder/JxlTocEncoder.cs

@@ -0,0 +1,55 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.Formats.Jxl.Fields;
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Processing.Encoder;
+
+internal static class JxlTocEncoder
+{
+    public static void WriteTocPermutation(Memory<int> permutation, JxlBitWriter writer)
+    {
+        int nPermutation = permutation.Length;
+
+        _ = writer.WithMaxBits((ulong)JxlToc.MaxBits(0), () =>
+        {
+            if (nPermutation > 0)
+            {
+                writer.Write(1, 1); // permutation present
+                if (!JxlCoefficientOrderEncoder.EncodePermutation(
+                    MemoryMarshal.Cast<int, uint>(permutation.Span),
+                    0,
+                    permutation.Length,
+                    writer))
+                {
+                    return false;
+                }
+            }
+            else
+            {
+                writer.Write(1, 0); // no permutation
+            }
+
+            writer.ZeroPadToByte();
+            return true;
+        });
+    }
+
+    public static void WriteTocSizes(Memory<int> groupSizes, JxlBitWriter writer) =>
+        _ = writer.WithMaxBits((ulong)JxlToc.MaxBits(groupSizes.Length), () =>
+        {
+            Span<int> groupSizesSpan = groupSizes.Span;
+
+            for (int i = 0; i < groupSizesSpan.Length; i++)
+            {
+                if (!JxlU32Coder.Write(in JxlToc.TocDistribution, unchecked((uint)groupSizesSpan[i]), writer))
+                {
+                    return false;
+                }
+            }
+
+            writer.ZeroPadToByte();
+            return true;
+        });
+}

src/ImageSharp/Formats/Jxl/Processing/JxlToc.cs

@@ -11,12 +11,22 @@ namespace SixLabors.ImageSharp.Formats.Jxl.Processing;
 /// </summary>
 internal static class JxlToc
 {
-    private static readonly JxlU32Enc TocDistribution = new(
+    private const int BitsPerByte = 8;
+
+    private const int MaxTocEntries = 65536;
+
+    public static readonly JxlU32Enc TocDistribution = new(
         JxlFieldExpressions.Bits(10),
         JxlFieldExpressions.BitsOffset(14, 2024),
         JxlFieldExpressions.BitsOffset(22, 17408),
         JxlFieldExpressions.BitsOffset(30, 4211712));
 
+    public static int MaxBits(int numSizes)
+    {
+        int entryBits = JxlU32Coder.MaxEncodedBits(TocDistribution) * numSizes;
+        return 1 + JxlMath.BitsPerByte + entryBits + JxlMath.BitsPerByte;
+    }
+
     public static int AcGroupIndex(int pass, int group, int numGroups, int numDcGroups)
         => 2 + numDcGroups + (pass * numGroups) + group;
 
@@ -30,10 +40,6 @@ internal static class JxlToc
         return AcGroupIndex(0, 0, numGroups, numDcGroups) + (numGroups * numPasses);
     }
 
-    private const int BitsPerByte = 8;
-
-    private const int MaxTocEntries = 65536;
-
     public static bool ReadToc(
         Configuration configuration,
         int tocEntries,