Update Adler32 to correctly filter intrinsics.

src/ImageSharp/Formats/Png/Zlib/Adler32.cs

@@ -63,7 +63,7 @@ public static uint Calculate(uint adler, ReadOnlySpan<byte> buffer)
             }
 
 #if SUPPORTS_RUNTIME_INTRINSICS
-            if (Sse3.IsSupported && buffer.Length >= MinBufferSize)
+            if (Ssse3.IsSupported && buffer.Length >= MinBufferSize)
             {
                 return CalculateSse(adler, buffer);
             }

tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs

@@ -2,14 +2,19 @@
 // Licensed under the Apache License, Version 2.0.
 
 // ReSharper disable InconsistentNaming
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
-
+#if SUPPORTS_RUNTIME_INTRINSICS
+using System.Runtime.Intrinsics.X86;
+#endif
+using Microsoft.DotNet.RemoteExecutor;
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
+using SixLabors.ImageSharp.Tests.TestUtilities;
 using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
 
 using Xunit;
@@ -529,6 +534,47 @@ public void Encode_WorksWithDiscontiguousBuffers<TPixel>(TestImageProvider<TPixe
             }
         }
 
+        [Theory]
+        [WithTestPatternImages(100, 100, PixelTypes.Rgba32)]
+        public void EncodeWorksWithoutSsse3Intrinsics<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            static void RunTest(string providerDump)
+            {
+                TestImageProvider<TPixel> provider =
+                    BasicSerializer.Deserialize<TestImageProvider<TPixel>>(providerDump);
+#if SUPPORTS_RUNTIME_INTRINSICS
+                Assert.False(Ssse3.IsSupported);
+#endif
+
+                foreach (PngInterlaceMode interlaceMode in InterlaceMode)
+                {
+                    TestPngEncoderCore(
+                        provider,
+                        PngColorType.Rgb,
+                        PngFilterMethod.Adaptive,
+                        PngBitDepth.Bit8,
+                        interlaceMode,
+                        appendPixelType: true,
+                        appendPngColorType: true);
+                }
+            }
+
+            string providerDump = BasicSerializer.Serialize(provider);
+
+            var processStartInfo = new ProcessStartInfo();
+            processStartInfo.Environment[TestEnvironment.Features.EnableSSE3] = TestEnvironment.Features.Off;
+
+            RemoteExecutor.Invoke(
+                RunTest,
+                providerDump,
+                new RemoteInvokeOptions
+                {
+                    StartInfo = processStartInfo
+                })
+                .Dispose();
+        }
+
         private static void TestPngEncoderCore<TPixel>(
             TestImageProvider<TPixel> provider,
             PngColorType pngColorType,

tests/ImageSharp.Tests/TestUtilities/TestEnvironment.Features.cs

@@ -0,0 +1,34 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Tests
+{
+    public static partial class TestEnvironment
+    {
+        internal static class Features
+        {
+            public const string On = "1";
+            public const string Off = "0";
+
+            public const string EnableAES = "COMPlus_EnableAES";
+            public const string EnableAVX = "COMPlus_EnableAVX";
+            public const string EnableAVX2 = "COMPlus_EnableAVX2";
+            public const string EnableBMI1 = "COMPlus_EnableBMI1";
+            public const string EnableBMI2 = "COMPlus_EnableBMI2";
+            public const string EnableFMA = "COMPlus_EnableFMA";
+            public const string EnableHWIntrinsic = "COMPlus_EnableHWIntrinsic";
+            public const string EnableIncompleteISAClass = "COMPlus_EnableIncompleteISAClass";
+            public const string EnableLZCNT = "COMPlus_EnableLZCNT";
+            public const string EnablePCLMULQDQ = "COMPlus_EnablePCLMULQDQ";
+            public const string EnablePOPCNT = "COMPlus_EnablePOPCNT";
+            public const string EnableSSE = "COMPlus_EnableSSE";
+            public const string EnableSSE2 = "COMPlus_EnableSSE2";
+            public const string EnableSSE3 = "COMPlus_EnableSSE3";
+            public const string EnableSSE3_4 = "COMPlus_EnableSSE3_4";
+            public const string EnableSSE41 = "COMPlus_EnableSSE41";
+            public const string EnableSSE42 = "COMPlus_EnableSSE42";
+            public const string EnableSSSE3 = "COMPlus_EnableSSSE3";
+            public const string FeatureSIMD = "COMPlus_FeatureSIMD";
+        }
+    }
+}