Avoid per-index multiply.

src/ImageSharp/Processing/Processors/Convolution/Convolution2DState.cs

@@ -31,24 +31,24 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
             this.columnOffsetMap = map.GetColumnOffsetSpan();
         }
 
-        public ReadOnlyKernel KernelY
+        public readonly ReadOnlyKernel KernelY
         {
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
             get;
         }
 
-        public ReadOnlyKernel KernelX
+        public readonly ReadOnlyKernel KernelX
         {
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
             get;
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public int GetRowSampleOffset(int row, int kernelRow)
-            => Unsafe.Add(ref MemoryMarshal.GetReference(this.rowOffsetMap), (row * this.kernelHeight) + kernelRow);
+        public readonly ref int GetSampleOffsetRow(int row)
+            => ref Unsafe.Add(ref MemoryMarshal.GetReference(this.rowOffsetMap), row * this.kernelHeight);
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public int GetColumnSampleOffset(int column, int kernelColumn)
-            => Unsafe.Add(ref MemoryMarshal.GetReference(this.columnOffsetMap), (column * this.kernelWidth) + kernelColumn);
+        public readonly ref int GetSampleOffsetColumn(int column)
+            => ref Unsafe.Add(ref MemoryMarshal.GetReference(this.columnOffsetMap), column * this.kernelWidth);
     }
 }

src/ImageSharp/Processing/Processors/Convolution/ConvolutionState.cs

@@ -28,18 +28,18 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
             this.columnOffsetMap = map.GetColumnOffsetSpan();
         }
 
-        public ReadOnlyKernel Kernel
+        public readonly ReadOnlyKernel Kernel
         {
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
             get;
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public int GetRowSampleOffset(int row, int kernelRow)
-            => Unsafe.Add(ref MemoryMarshal.GetReference(this.rowOffsetMap), (row * this.kernelHeight) + kernelRow);
+        public readonly ref int GetSampleOffsetRow(int row)
+            => ref Unsafe.Add(ref MemoryMarshal.GetReference(this.rowOffsetMap), row * this.kernelHeight);
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public int GetColumnSampleOffset(int column, int kernelColumn)
-            => Unsafe.Add(ref MemoryMarshal.GetReference(this.columnOffsetMap), (column * this.kernelWidth) + kernelColumn);
+        public readonly ref int GetSampleOffsetColumn(int column)
+            => ref Unsafe.Add(ref MemoryMarshal.GetReference(this.columnOffsetMap), column * this.kernelWidth);
     }
 }

src/ImageSharp/Processing/Processors/Convolution/Convolver.cs

@@ -100,14 +100,16 @@ namespace SixLabors.ImageSharp
             Vector4 vectorY = default;
             Vector4 vectorX = default;
 
+            ref int sampleOffsetRowBase = ref state.GetSampleOffsetRow(row);
             for (int y = 0; y < kernelHeight; y++)
             {
-                int offsetY = state.GetRowSampleOffset(row, y);
+                int offsetY = Unsafe.Add(ref sampleOffsetRowBase, y);
                 ref TPixel sourceRowBase = ref MemoryMarshal.GetReference(sourcePixels.GetRowSpan(offsetY));
+                ref int sampleOffsetColumnBase = ref state.GetSampleOffsetColumn(column);
 
                 for (int x = 0; x < kernelWidth; x++)
                 {
-                    int offsetX = state.GetColumnSampleOffset(column, x);
+                    int offsetX = Unsafe.Add(ref sampleOffsetColumnBase, x);
                     var sample = Unsafe.Add(ref sourceRowBase, offsetX).ToVector4();
                     Numerics.Premultiply(ref sample);
                     vectorX += kernelX[y, x] * sample;
@@ -199,14 +201,16 @@ namespace SixLabors.ImageSharp
             int kernelHeight = kernel.Rows;
             int kernelWidth = kernel.Columns;
 
+            ref int sampleOffsetRowBase = ref state.GetSampleOffsetRow(row);
             for (int y = 0; y < kernelHeight; y++)
             {
-                int offsetY = state.GetRowSampleOffset(row, y);
+                int offsetY = Unsafe.Add(ref sampleOffsetRowBase, y);
                 ref TPixel sourceRowBase = ref MemoryMarshal.GetReference(sourcePixels.GetRowSpan(offsetY));
+                ref int sampleOffsetColumnBase = ref state.GetSampleOffsetColumn(column);
 
                 for (int x = 0; x < kernelWidth; x++)
                 {
-                    int offsetX = state.GetColumnSampleOffset(column, x);
+                    int offsetX = Unsafe.Add(ref sampleOffsetColumnBase, x);
                     var sample = Unsafe.Add(ref sourceRowBase, offsetX).ToVector4();
                     Numerics.Premultiply(ref sample);
                     targetVector += kernel[y, x] * sample;

src/ImageSharp/Processing/Processors/Convolution/KernelSamplingMap.cs

@@ -52,9 +52,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
             ref int ySpanBase = ref MemoryMarshal.GetReference(ySpan);
             for (int row = 0; row < bounds.Height; row++)
             {
+                int rowBase = row * kernelHeight;
                 for (int y = 0; y < kernelHeight; y++)
                 {
-                    Unsafe.Add(ref ySpanBase, (row * kernelHeight) + y) = row + y + minY - radiusY;
+                    Unsafe.Add(ref ySpanBase, rowBase + y) = row + y + minY - radiusY;
                 }
             }
 
@@ -67,9 +68,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
             ref int xSpanBase = ref MemoryMarshal.GetReference(xSpan);
             for (int column = 0; column < bounds.Width; column++)
             {
+                int columnBase = column * kernelWidth;
                 for (int x = 0; x < kernelWidth; x++)
                 {
-                    Unsafe.Add(ref xSpanBase, (column * kernelWidth) + x) = column + x + minX - radiusX;
+                    Unsafe.Add(ref xSpanBase, columnBase + x) = column + x + minX - radiusX;
                 }
             }
 

tests/ImageSharp.Benchmarks/Config.cs

@@ -27,6 +27,14 @@ namespace SixLabors.ImageSharp.Benchmarks
 
         }
 
+        public class MultiFramework : Config
+        {
+            public MultiFramework() => this.AddJob(
+                    Job.Default.WithRuntime(ClrRuntime.Net472),
+                    Job.Default.WithRuntime(CoreRuntime.Core21),
+                    Job.Default.WithRuntime(CoreRuntime.Core31));
+        }
+
         public class ShortClr : Config
         {
             public ShortClr() => this.AddJob(

tests/ImageSharp.Benchmarks/Samplers/GaussianBlur.cs

@@ -7,7 +7,7 @@ using SixLabors.ImageSharp.Processing;
 
 namespace SixLabors.ImageSharp.Benchmarks.Samplers
 {
-    [Config(typeof(Config.ShortClr))]
+    [Config(typeof(Config.MultiFramework))]
     public class GaussianBlur
     {
         [Benchmark]