From 5904c7bb6d5f74d98d64c8c1c657cc822560eb5f Mon Sep 17 00:00:00 2001
From: Julius Friedman <jfriedman@cantaloupe.com>
Date: Fri, 25 Oct 2024 20:37:55 -0400
Subject: [PATCH] Fix up DerivedTable Fix up HuffmanTable.Tables Add ZigZag.

Trying to enjoy the weekend.
---
 Codecs/Image/Jpeg/Classes/DerivedTable.cs | 18 ++++++++++++------
 Codecs/Image/Jpeg/JpegCodec.cs            | 11 +++++++++++
 Codecs/Image/Jpeg/Markers/HuffmanTable.cs |  2 +-
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/Codecs/Image/Jpeg/Classes/DerivedTable.cs b/Codecs/Image/Jpeg/Classes/DerivedTable.cs
index 0ec221fe..18f3b9c4 100644
--- a/Codecs/Image/Jpeg/Classes/DerivedTable.cs
+++ b/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);
     }
 }
diff --git a/Codecs/Image/Jpeg/JpegCodec.cs b/Codecs/Image/Jpeg/JpegCodec.cs
index 19498c1b..3f158797 100644
--- a/Codecs/Image/Jpeg/JpegCodec.cs
+++ b/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++)
diff --git a/Codecs/Image/Jpeg/Markers/HuffmanTable.cs b/Codecs/Image/Jpeg/Markers/HuffmanTable.cs
index 259a1739..e47476c4 100644
--- a/Codecs/Image/Jpeg/Markers/HuffmanTable.cs
+++ b/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;
             }
         }
     }