Docs & review fixes

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverterBase.cs

@@ -39,7 +39,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
         /// Gets a value indicating how many pixels are processed in a single batch.
         /// </summary>
         /// <remarks>
-        /// This generaly should be equal to register size,
+        /// This generally should be equal to register size,
         /// e.g. 1 for scalar implementation, 8 for AVX implementation and so on.
         /// </remarks>
         public abstract int ElementsPerBatch { get; }

src/ImageSharp/Formats/Jpeg/Components/Decoder/ComponentProcessors/ComponentProcessor.cs

@@ -6,6 +6,9 @@ using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 {
+    /// <summary>
+    /// Base class for processing component spectral data and converting it to raw color data.
+    /// </summary>
     internal abstract class ComponentProcessor : IDisposable
     {
         public ComponentProcessor(MemoryAllocator memoryAllocator, JpegFrame frame, Size postProcessorBufferSize, IJpegComponent component, int blockSize)
@@ -28,8 +31,18 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
         protected Size BlockAreaSize { get; }
 
-        public abstract void CopyBlocksToColorBuffer(int spectralStep);
+        /// <summary>
+        /// Converts spectral data to color data accessible via <see cref="GetColorBufferRowSpan(int)"/>.
+        /// </summary>
+        /// <param name="row">Spectral row index to convert.</param>
+        public abstract void CopyBlocksToColorBuffer(int row);
 
+        /// <summary>
+        /// Clears spectral buffers.
+        /// </summary>
+        /// <remarks>
+        /// Should only be called during baseline interleaved decoding.
+        /// </remarks>
         public void ClearSpectralBuffers()
         {
             Buffer2D<Block8x8> spectralBlocks = this.Component.SpectralBlocks;
@@ -39,6 +52,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             }
         }
 
+        /// <summary>
+        /// Gets converted color buffer row.
+        /// </summary>
+        /// <param name="row">Row index.</param>
+        /// <returns>Color buffer row.</returns>
         public Span<float> GetColorBufferRowSpan(int row) =>
             this.ColorBuffer.DangerousGetRowSpan(row);
 

src/ImageSharp/Formats/Jpeg/Components/Decoder/ComponentProcessors/DirectComponentProcessor.cs

@@ -6,6 +6,9 @@ using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 {
+    /// <summary>
+    /// Processes component spectral data and converts it to color data in 1-to-1 scale.
+    /// </summary>
     internal sealed class DirectComponentProcessor : ComponentProcessor
     {
         private Block8x8F dequantizationTable;

src/ImageSharp/Formats/Jpeg/Components/Decoder/ComponentProcessors/DownScalingComponentProcessor2.cs

@@ -7,6 +7,9 @@ using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 {
+    /// <summary>
+    /// Processes component spectral data and converts it to color data in 2-to-1 scale.
+    /// </summary>
     internal sealed class DownScalingComponentProcessor2 : ComponentProcessor
     {
         private Block8x8F dequantizationTable;
@@ -88,7 +91,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                             for (int j = 0; j < horizontalScale; j++)
                             {
                                 // area[xx + j, yy + i] = value;
-                                Unsafe.Add(ref areaOrigin, baseIdx + j) = value;
+                                Unsafe.Add(ref areaOrigin, (nint)(uint)(baseIdx + j)) = value;
                             }
                         }
                     }

src/ImageSharp/Formats/Jpeg/Components/Decoder/ComponentProcessors/DownScalingComponentProcessor4.cs

@@ -7,6 +7,9 @@ using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 {
+    /// <summary>
+    /// Processes component spectral data and converts it to color data in 4-to-1 scale.
+    /// </summary>
     internal sealed class DownScalingComponentProcessor4 : ComponentProcessor
     {
         private Block8x8F dequantizationTable;
@@ -88,7 +91,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                             for (int j = 0; j < horizontalScale; j++)
                             {
                                 // area[xx + j, yy + i] = value;
-                                Unsafe.Add(ref areaOrigin, baseIdx + j) = value;
+                                Unsafe.Add(ref areaOrigin, (nint)(uint)(baseIdx + j)) = value;
                             }
                         }
                     }

src/ImageSharp/Formats/Jpeg/Components/Decoder/ComponentProcessors/DownScalingComponentProcessor8.cs

@@ -7,6 +7,9 @@ using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 {
+    /// <summary>
+    /// Processes component spectral data and converts it to color data in 8-to-1 scale.
+    /// </summary>
     internal sealed class DownScalingComponentProcessor8 : ComponentProcessor
     {
         private readonly float dcDequantizatizer;
@@ -63,10 +66,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
             if (horizontalScale == 2 && verticalScale == 2)
             {
-                Unsafe.Add(ref destRef, 0) = value;
+                destRef = value;
                 Unsafe.Add(ref destRef, 1) = value;
-                Unsafe.Add(ref destRef, 0 + destStrideWidth) = value;
-                Unsafe.Add(ref destRef, 1 + destStrideWidth) = value;
+                Unsafe.Add(ref destRef, 0 + (nint)(uint)destStrideWidth) = value;
+                Unsafe.Add(ref destRef, 1 + (nint)(uint)destStrideWidth) = value;
                 return;
             }
 
@@ -75,10 +78,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             {
                 for (int x = 0; x < horizontalScale; x++)
                 {
-                    Unsafe.Add(ref destRef, x) = value;
+                    Unsafe.Add(ref destRef, (nint)(uint)x) = value;
                 }
 
-                destRef = ref Unsafe.Add(ref destRef, destStrideWidth);
+                destRef = ref Unsafe.Add(ref destRef, (nint)(uint)destStrideWidth);
             }
         }
     }

tests/ImageSharp.Tests/Formats/Jpg/SpectralConverterTests.cs

@@ -9,6 +9,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
     [Trait("Format", "Jpg")]
     public class SpectralConverterTests
     {
+        // Test for null target size, i.e. when no scaling is needed
         [Theory]
         [InlineData(1, 1)]
         [InlineData(800, 400)]