Imported Upstream version 6.4.0.137

Former-commit-id: 943baa9f16a098c33e129777827f3a9d20da00d6

mcs/class/System.Private.CoreLib/System.Collections.Generic/EqualityComparer.cs

@@ -0,0 +1,79 @@
+using System.Runtime.CompilerServices;
+
+namespace System.Collections.Generic
+{
+	partial class EqualityComparer<T>
+	{
+		static volatile EqualityComparer<T> defaultComparer;
+
+		public static EqualityComparer<T> Default {
+			[MethodImplAttribute (MethodImplOptions.AggressiveInlining)]
+			get {
+				EqualityComparer<T> comparer = defaultComparer;
+				if (comparer == null) {
+					comparer = CreateComparer();
+					defaultComparer = comparer;
+				}
+				return comparer;
+			}
+		}
+
+		static EqualityComparer<T> CreateComparer ()
+		{
+			RuntimeType t = (RuntimeType)typeof(T);
+			if (t == typeof(byte)) {
+				return (EqualityComparer<T>)(object)(new ByteEqualityComparer());
+			}
+
+			/////////////////////////////////////////////////
+			// KEEP THIS IN SYNC WITH THE DEVIRT CODE
+			// IN METHOD-TO-IR.C
+			/////////////////////////////////////////////////
+
+			if (typeof(IEquatable<T>).IsAssignableFrom(t)) {
+				return (EqualityComparer<T>)RuntimeType.CreateInstanceForAnotherGenericParameter (typeof(GenericEqualityComparer<>), t);
+			}
+
+			if (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>)) {
+				RuntimeType u = (RuntimeType)t.GetGenericArguments()[0];
+				if (typeof(IEquatable<>).MakeGenericType(u).IsAssignableFrom(u)) {
+					return (EqualityComparer<T>)RuntimeType.CreateInstanceForAnotherGenericParameter (typeof(NullableEqualityComparer<>), u);
+				}
+			}
+
+			if (t.IsEnum) {
+				return (EqualityComparer<T>)RuntimeType.CreateInstanceForAnotherGenericParameter (typeof(EnumEqualityComparer<>), t);
+			}
+			
+			return new ObjectEqualityComparer<T>();
+		}
+
+		// MONOTODO: Add specialized versions
+		internal virtual int IndexOf (T[] array, T value, int startIndex, int count)
+		{
+			int endIndex = startIndex + count;
+			for (int i = startIndex; i < endIndex; i++) {
+				if (Equals (array[i], value))
+					return i;
+			}
+			return -1;
+		}
+
+		internal virtual int LastIndexOf (T[] array, T value, int startIndex, int count)
+		{
+			int endIndex = startIndex - count + 1;
+			for (int i = startIndex; i >= endIndex; i--) {
+				if (Equals (array[i], value))
+					return i;
+			}
+			return -1;
+		}
+
+	}
+
+	partial class EnumEqualityComparer<T>
+	{
+		[MethodImpl (MethodImplOptions.AggressiveInlining)]
+		public override bool Equals (T x, T y) => JitHelpers.EnumEquals (x, y);
+	}
+}