Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.ServiceModel/System/ServiceModel/StringUtil.cs

@@ -0,0 +1,63 @@
+// <copyright>
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+namespace System.ServiceModel
+{
+    internal static class StringUtil
+    {
+        private static readonly bool randomizedStringHashingEnabled;
+
+        static StringUtil()
+        {
+            // StringComparer.InvariantCultureIgnoreCase.GetHashCode is a stable hash between 32 and 64 bits. 
+            // Test the result of this GetHashCode against a known test vector to see if randomized hashing is enabled.
+            randomizedStringHashingEnabled = StringComparer.InvariantCultureIgnoreCase.GetHashCode("The quick brown fox jumps over the lazy dog.") != 0x703e662e;
+        }
+
+        // This should be used instead of String.GetHashCode if the value should be
+        // stable even if UseRandomizedStringHashing is enabled.
+        internal static int GetNonRandomizedHashCode(string str)
+        {
+            if (!randomizedStringHashingEnabled)
+            {
+                return str.GetHashCode();
+            }
+
+            return GetStableHashCode(str);
+        }
+
+        // This is copied from the 32 bit implementation from String.GetHashCode.
+        // Since ServiceModel is compiled for MSIL, we can't have different functionality
+        // for 32 and 64 bits.
+        [System.Security.SecuritySafeCritical]
+        private static int GetStableHashCode(string str)
+        {
+            unsafe 
+            {
+                fixed (char* src = str) 
+                {
+                    int hash1 = (5381 << 16) + 5381;
+                    int hash2 = hash1;
+
+                    // 32 bit machines.
+                    int* pint = (int*)src;
+                    int len = str.Length;
+                    while (len > 2)
+                    {
+                        hash1 = ((hash1 << 5) + hash1 + (hash1 >> 27)) ^ pint[0];
+                        hash2 = ((hash2 << 5) + hash2 + (hash2 >> 27)) ^ pint[1];
+                        pint += 2;
+                        len  -= 4;
+                    }
+
+                    if (len > 0)
+                    {
+                        hash1 = ((hash1 << 5) + hash1 + (hash1 >> 27)) ^ pint[0];
+                    }
+
+                    return hash1 + (hash2 * 1566083941);
+                }
+            }
+        }
+    }
+}