reapply unsafe optimizations

src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeKernel.cs

@@ -55,11 +55,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
         [MethodImpl(InliningOptions.ShortMethod)]
         public Vector4 Convolve(Span<Vector4> rowSpan)
         {
-            return this.ConvolveCore(rowSpan.Slice(this.StartIndex));
+            return this.ConvolveCore(ref rowSpan[this.StartIndex]);
         }
 
         [MethodImpl(InliningOptions.ShortMethod)]
-        public Vector4 ConvolveCore(Span<Vector4> offsetedRowSpan)
+        public Vector4 ConvolveCore(ref Vector4 rowStartRef)
         {
             ref float horizontalValues = ref Unsafe.AsRef<float>(this.bufferPtr);
 
@@ -70,8 +70,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             {
                 float weight = Unsafe.Add(ref horizontalValues, i);
 
-                // Vector4 v = Unsafe.Add(ref rowStartRef, i);
-                Vector4 v = offsetedRowSpan[i];
+                // Vector4 v = offsetedRowSpan[i];
+                Vector4 v = Unsafe.Add(ref rowStartRef, i);
                 result += v * weight;
             }
 

src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeWorker.cs

@@ -125,10 +125,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
 
                 for (int x = 0; x < this.destWidth; x++)
                 {
-                    Span<Vector4> firstPassColumn = this.GetColumnSpan(x).Slice(top);
+                    // Span<Vector4> firstPassColumn = this.GetColumnSpan(x).Slice(top);
+                    ref Vector4 firstPassColumnBase = ref this.GetColumnSpan(x)[top];
 
                     // Destination color components
-                    Unsafe.Add(ref tempRowBase, x) = kernel.ConvolveCore(firstPassColumn);
+                    Unsafe.Add(ref tempRowBase, x) = kernel.ConvolveCore(ref firstPassColumnBase);
                 }
 
                 Span<TPixel> targetRowSpan = destination.GetRowSpan(y);
@@ -174,15 +175,15 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
                     tempRowSpan,
                     this.conversionModifiers);
 
-                // ref Vector4 firstPassBaseRef = ref this.buffer.Span[y - top];
-                Span<Vector4> firstPassSpan = this.transposedFirstPassBuffer.Span.Slice(y - this.currentWindow.Min);
+                // Span<Vector4> firstPassSpan = this.transposedFirstPassBuffer.Span.Slice(y - this.currentWindow.Min);
+                ref Vector4 firstPassBaseRef = ref this.transposedFirstPassBuffer.Span[y - this.currentWindow.Min];
 
                 for (int x = this.targetWorkingRect.Left; x < this.targetWorkingRect.Right; x++)
                 {
                     ResizeKernel kernel = this.horizontalKernelMap.GetKernel(x - this.targetOrigin.X);
-                    firstPassSpan[x * this.workerHeight] = kernel.Convolve(tempRowSpan);
 
-                    // Unsafe.Add(ref firstPassBaseRef, x * this.sourceRectangle.Height) = kernel.Convolve(tempRowSpan);
+                    // firstPassSpan[x * this.workerHeight] = kernel.Convolve(tempRowSpan);
+                    Unsafe.Add(ref firstPassBaseRef, x * this.workerHeight) = kernel.Convolve(tempRowSpan);
                 }
             }
         }