Added test for TransposeInplace

tests/ImageSharp.Tests/Formats/Jpg/Block8x8FTests.cs

@@ -183,9 +183,12 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                 Assert.Equal(expected, actual);
             }
 
+            // This method has only 2 implementations:
+            // 1. AVX
+            // 2. Scalar
             FeatureTestRunner.RunWithHwIntrinsicsFeature(
                 RunTest,
-                HwIntrinsics.AllowAll | HwIntrinsics.DisableAVX | HwIntrinsics.DisableHWIntrinsic);
+                HwIntrinsics.AllowAll | HwIntrinsics.DisableHWIntrinsic);
         }
 
         private static float[] Create8x8ColorCropTestData()

tests/ImageSharp.Tests/Formats/Jpg/Block8x8Tests.cs

@@ -276,5 +276,31 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                 seed,
                 HwIntrinsics.AllowAll | HwIntrinsics.DisableAVX2);
         }
+
+        [Fact]
+        public void TransposeInplace()
+        {
+            static void RunTest()
+            {
+                short[] expected = Create8x8ShortData();
+                ReferenceImplementations.Transpose8x8(expected);
+
+                var block8x8 = default(Block8x8);
+                block8x8.LoadFrom(Create8x8ShortData());
+
+                block8x8.TransposeInplace();
+
+                short[] actual = new short[64];
+                block8x8.CopyTo(actual);
+
+                Assert.Equal(expected, actual);
+            }
+
+            // This method has only 1 implementation:
+            // 1. Scalar
+            FeatureTestRunner.RunWithHwIntrinsicsFeature(
+                RunTest,
+                HwIntrinsics.DisableHWIntrinsic);
+        }
     }
 }

tests/ImageSharp.Tests/Formats/Jpg/Utils/ReferenceImplementations.cs

@@ -40,6 +40,23 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg.Utils
             }
         }
 
+        /// <summary>
+        /// Transpose 8x8 block stored linearly in a <see cref="Span{T}"/> (inplace)
+        /// </summary>
+        internal static void Transpose8x8(Span<short> data)
+        {
+            for (int i = 1; i < 8; i++)
+            {
+                int i8 = i * 8;
+                for (int j = 0; j < i; j++)
+                {
+                    short tmp = data[i8 + j];
+                    data[i8 + j] = data[(j * 8) + i];
+                    data[(j * 8) + i] = tmp;
+                }
+            }
+        }
+
         /// <summary>
         /// Transpose 8x8 block stored linearly in a  <see cref="Span{T}"/>
         /// </summary>