1 files changed, 38 insertions, 0 deletions
diff --git a/src/System.Private.CoreLib/shared/System/Collections/Generic/NonRandomizedStringEqualityComparer.cs b/src/System.Private.CoreLib/shared/System/Collections/Generic/NonRandomizedStringEqualityComparer.cs
new file mode 100644
index 000000000..ef44fefc8
--- /dev/null
+++ b/src/System.Private.CoreLib/shared/System/Collections/Generic/NonRandomizedStringEqualityComparer.cs
@@ -0,0 +1,38 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Runtime.Serialization;
+
+namespace System.Collections.Generic
+{
+    // NonRandomizedStringEqualityComparer is the comparer used by default with the Dictionary<string,...> 
+    // We use NonRandomizedStringEqualityComparer as default comparer as it doesnt use the randomized string hashing which 
+    // keeps the performance not affected till we hit collision threshold and then we switch to the comparer which is using 
+    // randomized string hashing.
+    [Serializable] // Required for compatibility with .NET Core 2.0 as we exposed the NonRandomizedStringEqualityComparer inside the serialization blob
+#if CORECLR
+    internal
+#else
+    public
+#endif
+    sealed class NonRandomizedStringEqualityComparer : EqualityComparer<string>, ISerializable
+    {
+        internal static new IEqualityComparer<string> Default { get; } = new NonRandomizedStringEqualityComparer();
+
+        private NonRandomizedStringEqualityComparer() { }
+
+        // This is used by the serialization engine.
+        private NonRandomizedStringEqualityComparer(SerializationInfo information, StreamingContext context) { }
+
+        public sealed override bool Equals(string x, string y) => string.Equals(x, y);
+
+        public sealed override int GetHashCode(string obj) => obj?.GetLegacyNonRandomizedHashCode() ?? 0;
+
+        public void GetObjectData(SerializationInfo info, StreamingContext context)
+        {
+            // We are doing this to stay compatible with .NET Framework.
+            info.SetType(typeof(GenericEqualityComparer<string>));
+        }
+    }
+}