1 files changed, 142 insertions, 0 deletions
diff --git a/src/System.Private.CoreLib/shared/System/Resources/FastResourceComparer.cs b/src/System.Private.CoreLib/shared/System/Resources/FastResourceComparer.cs
new file mode 100644
index 000000000..6b813a0ce
--- /dev/null
+++ b/src/System.Private.CoreLib/shared/System/Resources/FastResourceComparer.cs
@@ -0,0 +1,142 @@
+// 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.
+
+/*============================================================
+**
+** 
+** 
+**
+**
+** Purpose: A collection of quick methods for comparing 
+**          resource keys (strings)
+**
+** 
+===========================================================*/
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Diagnostics;
+
+namespace System.Resources
+{
+    internal sealed class FastResourceComparer : IComparer, IEqualityComparer, IComparer<string>, IEqualityComparer<string>
+    {
+        internal static readonly FastResourceComparer Default = new FastResourceComparer();
+
+        // Implements IHashCodeProvider too, due to Hashtable requirements.
+        public int GetHashCode(object key)
+        {
+            string s = (string)key;
+            return FastResourceComparer.HashFunction(s);
+        }
+
+        public int GetHashCode(string key)
+        {
+            return FastResourceComparer.HashFunction(key);
+        }
+
+        // This hash function MUST be publically documented with the resource
+        // file format, AND we may NEVER change this hash function's return 
+        // value (without changing the file format).
+        internal static int HashFunction(string key)
+        {
+            // Never change this hash function.  We must standardize it so that 
+            // others can read & write our .resources files.  Additionally, we
+            // have a copy of it in InternalResGen as well.
+            uint hash = 5381;
+            for (int i = 0; i < key.Length; i++)
+                hash = ((hash << 5) + hash) ^ key[i];
+            return (int)hash;
+        }
+
+        // Compares Strings quickly in a case-sensitive way
+        public int Compare(object a, object b)
+        {
+            if (a == b) return 0;
+            string sa = (string)a;
+            string sb = (string)b;
+            return string.CompareOrdinal(sa, sb);
+        }
+
+        public int Compare(string a, string b)
+        {
+            return string.CompareOrdinal(a, b);
+        }
+
+        public bool Equals(string a, string b)
+        {
+            return string.Equals(a, b);
+        }
+
+        public new bool Equals(object a, object b)
+        {
+            if (a == b) return true;
+            string sa = (string)a;
+            string sb = (string)b;
+            return string.Equals(sa, sb);
+        }
+
+        // Input is one string to compare with, and a byte[] containing chars in 
+        // little endian unicode.  Pass in the number of valid chars.
+        public static unsafe int CompareOrdinal(string a, byte[] bytes, int bCharLength)
+        {
+            Debug.Assert(a != null && bytes != null, "FastResourceComparer::CompareOrdinal must have non-null params");
+            Debug.Assert(bCharLength * 2 <= bytes.Length, "FastResourceComparer::CompareOrdinal - numChars is too big!");
+            // This is a managed version of strcmp, but I can't take advantage
+            // of a terminating 0, unlike strcmp in C.
+            int i = 0;
+            int r = 0;
+            // Compare the min length # of characters, then return length diffs.
+            int numChars = a.Length;
+            if (numChars > bCharLength)
+                numChars = bCharLength;
+            if (bCharLength == 0)   // Can't use fixed on a 0-element array.
+                return (a.Length == 0) ? 0 : -1;
+            fixed (byte* pb = bytes)
+            {
+                byte* pChar = pb;
+                while (i < numChars && r == 0)
+                {
+                    // little endian format
+                    int b = pChar[0] | pChar[1] << 8;
+                    r = a[i++] - b;
+                    pChar += sizeof(char);
+                }
+            }
+            if (r != 0) return r;
+            return a.Length - bCharLength;
+        }
+
+        public static int CompareOrdinal(byte[] bytes, int aCharLength, string b)
+        {
+            return -CompareOrdinal(b, bytes, aCharLength);
+        }
+
+        // This method is to handle potentially misaligned data accesses.
+        // The byte* must point to little endian Unicode characters.
+        internal static unsafe int CompareOrdinal(byte* a, int byteLen, string b)
+        {
+            Debug.Assert((byteLen & 1) == 0, "CompareOrdinal is expecting a UTF-16 string length, which must be even!");
+            Debug.Assert(a != null && b != null, "Null args not allowed.");
+            Debug.Assert(byteLen >= 0, "byteLen must be non-negative.");
+
+            int r = 0;
+            int i = 0;
+            // Compare the min length # of characters, then return length diffs.
+            int numChars = byteLen >> 1;
+            if (numChars > b.Length)
+                numChars = b.Length;
+            while (i < numChars && r == 0)
+            {
+                // Must compare character by character, not byte by byte.
+                char aCh = (char)(*a++ | (*a++ << 8));
+                r = aCh - b[i++];
+            }
+            if (r != 0) return r;
+            return byteLen - b.Length * 2;
+        }
+    }
+}
+