Merge pull request #1922 from br3aker/dp/jpeg-idct-scalar

Fixed Jpeg IDCT missing scalar implementation

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

@@ -146,11 +146,13 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
         /// <summary>
         /// Apply floating point IDCT inplace using <see cref="Vector4"/> API.
         /// </summary>
+        /// <remarks>
+        /// This method can be used even if there's no SIMD intrinsics available
+        /// as <see cref="Vector4"/> can be compiled to scalar instructions.
+        /// </remarks>
         /// <param name="transposedBlock">Input block.</param>
         private static void IDCT_Vector4(ref Block8x8F transposedBlock)
         {
-            DebugGuard.IsTrue(Vector.IsHardwareAccelerated, "Scalar implementation should be called for non-accelerated hardware.");
-
             // First pass - process columns
             IDCT8x4_Vector4(ref transposedBlock.V0L);
             IDCT8x4_Vector4(ref transposedBlock.V0R);

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

@@ -149,12 +149,12 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                 // 4 paths:
                 // 1. AllowAll - call avx/fma implementation
                 // 2. DisableFMA - call avx without fma implementation
-                // 3. DisableAvx - call sse Vector4 implementation
-                // 4. DisableHWIntrinsic - call scalar fallback implementation
+                // 3. DisableAvx - call sse implementation
+                // 4. DisableSIMD - call Vector4 fallback implementation
                 FeatureTestRunner.RunWithHwIntrinsicsFeature(
                     RunTest,
                     seed,
-                    HwIntrinsics.AllowAll | HwIntrinsics.DisableFMA | HwIntrinsics.DisableAVX | HwIntrinsics.DisableHWIntrinsic);
+                    HwIntrinsics.AllowAll | HwIntrinsics.DisableFMA | HwIntrinsics.DisableAVX | HwIntrinsics.DisableSIMD);
             }
 
             // Forward transform
@@ -197,12 +197,12 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                 // 4 paths:
                 // 1. AllowAll - call avx/fma implementation
                 // 2. DisableFMA - call avx without fma implementation
-                // 3. DisableAvx - call sse Vector4 implementation
-                // 4. DisableHWIntrinsic - call scalar fallback implementation
+                // 3. DisableAvx - call Vector4 implementation
+                // 4. DisableSIMD - call scalar fallback implementation
                 FeatureTestRunner.RunWithHwIntrinsicsFeature(
                     RunTest,
                     seed,
-                    HwIntrinsics.AllowAll | HwIntrinsics.DisableFMA | HwIntrinsics.DisableAVX | HwIntrinsics.DisableHWIntrinsic);
+                    HwIntrinsics.AllowAll | HwIntrinsics.DisableFMA | HwIntrinsics.DisableAVX | HwIntrinsics.DisableSIMD);
             }
         }
     }