Add support for decoding jpeg's with arithmetic coding

src/ImageSharp/Formats/Bmp/BmpDecoderCore.cs

@@ -116,7 +116,7 @@ public BmpDecoderCore(Configuration configuration, IBmpDecoderOptions options)
         /// <summary>
         /// Gets the dimensions of the image.
         /// </summary>
-        public Size Dimensions => new Size(this.infoHeader.Width, this.infoHeader.Height);
+        public Size Dimensions => new(this.infoHeader.Width, this.infoHeader.Height);
 
         /// <inheritdoc />
         public Image<TPixel> Decode<TPixel>(BufferedReadStream stream, CancellationToken cancellationToken)
@@ -389,7 +389,7 @@ private void ReadRle24<TPixel>(Buffer2D<TPixel> pixels, int width, int height, b
                     if (rowHasUndefinedPixels)
                     {
                         // Slow path with undefined pixels.
-                        var yMulWidth = y * width;
+                        int yMulWidth = y * width;
                         int rowStartIdx = yMulWidth * 3;
                         for (int x = 0; x < width; x++)
                         {

src/ImageSharp/Formats/Jpeg/Components/ComponentType.cs

@@ -0,0 +1,12 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Jpeg.Components
+{
+    internal enum ComponentType
+    {
+        Huffman = 0,
+
+        Arithmetic = 1
+    }
+}

src/ImageSharp/Formats/Jpeg/Components/Decoder/ArithmeticDecodingComponent.cs

@@ -0,0 +1,30 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
+{
+    internal class ArithmeticDecodingComponent : JpegComponent
+    {
+        public ArithmeticDecodingComponent(MemoryAllocator memoryAllocator, JpegFrame frame, byte id, int horizontalFactor, int verticalFactor, byte quantizationTableIndex, int index)
+            : base(memoryAllocator, frame, id, horizontalFactor, verticalFactor, quantizationTableIndex, index)
+        {
+        }
+
+        /// <summary>
+        /// Gets or sets the dc context.
+        /// </summary>
+        public int DcContext { get; set; }
+
+        /// <summary>
+        /// Gets or sets the dc statistics.
+        /// </summary>
+        public ArithmeticStatistics DcStatistics { get; set; }
+
+        /// <summary>
+        /// Gets or sets the ac statistics.
+        /// </summary>
+        public ArithmeticStatistics AcStatistics { get; set; }
+    }
+}

src/ImageSharp/Formats/Jpeg/Components/Decoder/ArithmeticDecodingTable.cs

@@ -0,0 +1,43 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
+{
+    internal class ArithmeticDecodingTable
+    {
+        public ArithmeticDecodingTable(byte tableClass, byte identifier)
+        {
+            this.TableClass = tableClass;
+            this.Identifier = identifier;
+        }
+
+        public byte TableClass { get; }
+
+        public byte Identifier { get; }
+
+        public byte ConditioningTableValue { get; private set; }
+
+        public int DcL { get; private set; }
+
+        public int DcU { get; private set; }
+
+        public int AcKx { get; private set; }
+
+        public void Configure(byte conditioningTableValue)
+        {
+            this.ConditioningTableValue = conditioningTableValue;
+            if (this.TableClass == 0)
+            {
+                this.DcL = conditioningTableValue & 0x0F;
+                this.DcU = conditioningTableValue >> 4;
+                this.AcKx = 0;
+            }
+            else
+            {
+                this.DcL = 0;
+                this.DcU = 0;
+                this.AcKx = conditioningTableValue;
+            }
+        }
+    }
+}