From b299e1a2f7600f1611be32be0b703ba2b24dddb6 Mon Sep 17 00:00:00 2001
From: Dmitry Pentin <riotbr3aker@gmail.com>
Date: Thu, 15 Jul 2021 19:04:03 +0300
Subject: [PATCH] Scan component count refactor

---
 .../Components/Decoder/HuffmanScanDecoder.cs  | 24 ++++++++++---------
 .../Formats/Jpeg/JpegDecoderCore.cs           |  8 +------
 2 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanScanDecoder.cs b/src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanScanDecoder.cs
index 688414b33..ea76df7a8 100644
--- a/src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanScanDecoder.cs
+++ b/src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanScanDecoder.cs
@@ -22,6 +22,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         private JpegFrame frame;
         private JpegComponent[] components;
 
+        // The number of interleaved components.
+        private int componentsCount;
+
         /// <summary>
         /// The reset interval determined by RST markers.
         /// </summary>
@@ -86,9 +89,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             }
         }
 
-        // The number of interleaved components.
-        public int ComponentsLength { get; set; }
-
         // The spectral selection start.
         public int SpectralStart { get; set; }
 
@@ -104,10 +104,12 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// <summary>
         /// Decodes the entropy coded data.
         /// </summary>
-        public void ParseEntropyCodedData()
+        public void ParseEntropyCodedData(int componentCount)
         {
             this.cancellationToken.ThrowIfCancellationRequested();
 
+            this.componentsCount = componentCount;
+
             this.scanBuffer = new HuffmanScanBuffer(this.stream);
 
             bool fullScan = this.frame.Progressive || this.frame.MultiScan;
@@ -138,7 +140,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
         private void ParseBaselineData()
         {
-            if (this.ComponentsLength == this.frame.ComponentCount)
+            if (this.componentsCount == this.frame.ComponentCount)
             {
                 this.ParseBaselineDataInterleaved();
             }
@@ -157,7 +159,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             ref HuffmanScanBuffer buffer = ref this.scanBuffer;
 
             // Pre-derive the huffman table to avoid in-loop checks.
-            for (int i = 0; i < this.ComponentsLength; i++)
+            for (int i = 0; i < this.componentsCount; i++)
             {
                 int order = this.frame.ComponentOrder[i];
                 JpegComponent component = this.components[order];
@@ -177,7 +179,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                 {
                     // Scan an interleaved mcu... process components in order
                     int mcuCol = mcu % mcusPerLine;
-                    for (int k = 0; k < this.ComponentsLength; k++)
+                    for (int k = 0; k < this.componentsCount; k++)
                     {
                         int order = this.frame.ComponentOrder[k];
                         JpegComponent component = this.components[order];
@@ -286,7 +288,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                 }
 
                 // AC scans may have only one component.
-                if (this.ComponentsLength != 1)
+                if (this.componentsCount != 1)
                 {
                     invalid = true;
                 }
@@ -318,7 +320,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         {
             this.CheckProgressiveData();
 
-            if (this.ComponentsLength == 1)
+            if (this.componentsCount == 1)
             {
                 this.ParseProgressiveDataNonInterleaved();
             }
@@ -337,7 +339,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             ref HuffmanScanBuffer buffer = ref this.scanBuffer;
 
             // Pre-derive the huffman table to avoid in-loop checks.
-            for (int k = 0; k < this.ComponentsLength; k++)
+            for (int k = 0; k < this.componentsCount; k++)
             {
                 int order = this.frame.ComponentOrder[k];
                 JpegComponent component = this.components[order];
@@ -352,7 +354,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                     // Scan an interleaved mcu... process components in order
                     int mcuRow = mcu / mcusPerLine;
                     int mcuCol = mcu % mcusPerLine;
-                    for (int k = 0; k < this.ComponentsLength; k++)
+                    for (int k = 0; k < this.componentsCount; k++)
                     {
                         int order = this.frame.ComponentOrder[k];
                         JpegComponent component = this.components[order];
diff --git a/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs b/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs
index e61909798..97a6d3999 100644
--- a/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs
+++ b/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs
@@ -1044,19 +1044,13 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             int spectralEnd = this.temp[1];
             int successiveApproximation = this.temp[2];
 
-            // All the comments below are for separate refactoring PR
-            // Main reason it's not fixed here is to make this commit less intrusive
-
-            // This can be passed as ParseEntropyCodedData() parameter as it is used only there
-            this.scanDecoder.ComponentsLength = selectorsCount;
-
             // This is okay to inject here, might be good to wrap it in a separate struct but not really necessary
             this.scanDecoder.SpectralStart = spectralStart;
             this.scanDecoder.SpectralEnd = spectralEnd;
             this.scanDecoder.SuccessiveHigh = successiveApproximation >> 4;
             this.scanDecoder.SuccessiveLow = successiveApproximation & 15;
 
-            this.scanDecoder.ParseEntropyCodedData();
+            this.scanDecoder.ParseEntropyCodedData(selectorsCount);
         }
 
         /// <summary>