Add nint optimization

src/ImageSharp/Formats/Jpeg/Components/Block8x8F.cs

@@ -104,7 +104,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
             {
                 GuardBlockIndex(idx);
                 ref float selfRef = ref Unsafe.As<Block8x8F, float>(ref this);
-                return Unsafe.Add(ref selfRef, idx);
+                return Unsafe.Add(ref selfRef, (nint)(uint)idx);
             }
 
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -112,7 +112,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
             {
                 GuardBlockIndex(idx);
                 ref float selfRef = ref Unsafe.As<Block8x8F, float>(ref this);
-                Unsafe.Add(ref selfRef, idx) = value;
+                Unsafe.Add(ref selfRef, (nint)(uint)idx) = value;
             }
         }
 

src/ImageSharp/Formats/Jpeg/Components/Encoder/RgbForwardConverter{TPixel}.cs

@@ -103,7 +103,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
 
             for (int i = 0; i < Block8x8F.Size; i++)
             {
-                Rgb24 c = Unsafe.Add(ref rgbStart, i);
+                Rgb24 c = Unsafe.Add(ref rgbStart, (nint)(uint)i);
 
                 redBlock[i] = c.R;
                 greenBlock[i] = c.G;

src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs

@@ -167,14 +167,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <param name="colorType">The color type.</param>
         /// <returns>true, if color type is supported.</returns>
         private static bool IsSupportedColorType(JpegColorType? colorType)
-        {
+            => colorType == JpegColorType.YCbCrRatio444
-            if (colorType == JpegColorType.YCbCrRatio444 || colorType == JpegColorType.YCbCrRatio420 || colorType == JpegColorType.Luminance || colorType == JpegColorType.Rgb)
+            || colorType == JpegColorType.YCbCrRatio420
-            {
+            || colorType == JpegColorType.Luminance
-                return true;
+            || colorType == JpegColorType.Rgb;
-            }
-
-            return false;
-        }
 
         /// <summary>
         /// Gets the component ids.