Fix up DerivedTable

Fix up HuffmanTable.Tables
Add ZigZag.

Trying to enjoy the weekend.

Codecs/Image/Jpeg/Classes/DerivedTable.cs

@@ -5,12 +5,18 @@ namespace Codec.Jpeg.Classes;
 
 internal class DerivedTable : MemorySegment
 {
-    public const int Length = 17;
+    public const int Length = 1;
+
+    public const int CodeLength = 16;
 
     public DerivedTable(MemorySegment segment) : base(segment)
     {
     }
 
+    public DerivedTable(int size) : base(new byte[Length + size])
+    {
+    }
+
     /// <summary>
     /// Table class, 0 = DC table or lossless table, 1 = AC table
     /// Baseline 0 or 1, Progressive DCT or Lossless = 0
@@ -52,11 +58,11 @@ public int Th
     /// </summary>
     public MemorySegment Li
     {
-        get => this.Slice(Offset + 1, Length - 1);
-        set => value.CopyTo(Array, Offset + 1, Length - 1);
+        get => this.Slice(Offset + Length, CodeLength);
+        set => value.CopyTo(Array, Offset + Length, CodeLength);
     }
 
-    public int ValuesCount 
+    public int CodeLengthSum 
     {
         get
         {
@@ -70,7 +76,7 @@ public int ValuesCount
     /// </summary>
     public MemorySegment Vi
     {
-        get => this.Slice(Offset + Length, ValuesCount);
-        set => value.CopyTo(Array, Offset + Length, ValuesCount);
+        get => this.Slice(Offset + CodeLength, CodeLengthSum);
+        set => value.CopyTo(Array, Offset + CodeLength, CodeLengthSum);
     }
 }

Codecs/Image/Jpeg/JpegCodec.cs

@@ -283,6 +283,17 @@ internal static void Decompress(JpegImage jpegImage)
 
         #region Compress
 
+        internal ReadOnlySpan<byte> ZigZag => [
+             0, 1, 5, 6,14,15,27,28,
+             2, 4, 7,13,16,26,29,42,
+             3, 8,12,17,25,30,41,43,
+             9,11,18,24,31,40,44,53,
+            10,19,23,32,39,45,52,54,
+            20,22,33,38,46,51,55,60,
+            21,34,37,47,50,56,59,61,
+            35,36,48,49,57,58,62,63
+        ];
+
         internal static void FDCT(Span<double> input, Span<double> output)
         {
             for (int u = 0; u < BlockSize; u++)

Codecs/Image/Jpeg/Markers/HuffmanTable.cs

@@ -33,7 +33,7 @@ internal IEnumerable<DerivedTable> Tables
                 using var slice = this.Slice(offset);
                 using var derivedTable = new DerivedTable(slice);
                 yield return derivedTable;
-                offset += DerivedTable.Length + derivedTable.ValuesCount;
+                offset += DerivedTable.Length + DerivedTable.CodeLength + derivedTable.CodeLengthSum;
             }
         }
     }