Add RuntimeHelpers for netstandard2.0

JustArchiNET.Madness/RuntimeHelpers/RuntimeHelpers.cs

@@ -0,0 +1,75 @@
+//                             _         __  __
+//  ___  ___   ___  _ __    __| |  __ _ |  \/  |
+// / __|/ __| / _ \| '_ \  / _` | / _` || |\/| |
+// \__ \\__ \|  __/| | | || (_| || (_| || |  | |
+// |___/|___/ \___||_| |_| \__,_| \__,_||_|  |_|
+// |
+// Copyright 2021-2022 Łukasz "JustArchi" Domeradzki
+// Contact: [email protected]
+// |
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// |
+// http://www.apache.org/licenses/LICENSE-2.0
+// |
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#if !NETSTANDARD2_1_OR_GREATER
+using System.Runtime.InteropServices;
+using JetBrains.Annotations;
+using JustArchiNET.Madness.Helpers;
+
+// ReSharper disable once CheckNamespace - we intentionally declare this namespace
+namespace System.Runtime.CompilerServices;
+
+[MadnessType(EMadnessType.Implementation)]
+[PublicAPI]
+public static class RuntimeHelpers {
+	public static int OffsetToStringData {
+		get {
+			switch (RuntimeInformation.ProcessArchitecture) {
+				case Architecture.Arm:
+				case Architecture.X86:
+					return 8;
+				default:
+					return 12;
+			}
+		}
+	}
+
+	/// <summary>
+	///     Slices the specified array using the specified range.
+	/// </summary>
+	public static T[] GetSubArray<T>(T[] array, Range range) {
+		if (array == null) {
+			throw new ArgumentNullException(nameof(array));
+		}
+
+		(int offset, int length) = range.GetOffsetAndLength(array.Length);
+
+		T[] dest;
+
+		if (typeof(T).IsValueType || (typeof(T[]) == array.GetType())) {
+			// We know the type of the array to be exactly T[].
+
+			if (length == 0) {
+				return Array.Empty<T>();
+			}
+
+			dest = new T[length];
+			Array.Copy(array, offset, dest, 0, length);
+		} else {
+			// The array is actually a U[] where U:T.
+			dest = (T[]) Array.CreateInstance(array.GetType().GetElementType()!, length);
+			Array.Copy(array, offset, dest, 0, length);
+		}
+
+		return dest;
+	}
+}
+#endif