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diff --git a/vespajlib/src/main/java/com/yahoo/collections/MD5.java b/vespajlib/src/main/java/com/yahoo/collections/MD5.java
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+++ b/vespajlib/src/main/java/com/yahoo/collections/MD5.java
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+// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.collections;
+
+import com.yahoo.text.Utf8;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
+/**
+ * Convenience class for hashing a String with MD5, and either returning
+ * an int with the 4 LSBytes, or the whole 12-byte MD5 hash.
+ * <p>
+ * Note that instantiating this class can be expensive, so re-using instances
+ * is a good idea.
+ * <p>
+ * This class is not thread safe.
+ *
+ * @author <a href="mailto:einarmr@yahoo-inc.com">Einar M R Rosenvinge</a>
+ */
+public class MD5 {
+    public static final ThreadLocal<MessageDigest> md5 = new MD5Factory();
+
+    private static class MD5Factory extends ThreadLocal<MessageDigest> {
+
+        @Override
+        protected MessageDigest initialValue() {
+            return createMD5();
+        }
+    }
+    private static MessageDigest createMD5() {
+        try {
+            return MessageDigest.getInstance("MD5");
+        } catch (NoSuchAlgorithmException e) {
+            throw new RuntimeException(e);
+        }
+    }
+    final private MessageDigest digester;
+    public MD5() {
+        try {
+            digester = MessageDigest.getInstance("MD5");
+        } catch (NoSuchAlgorithmException e) {
+            throw new AssertionError("MD5 algorithm not found.");
+        }
+    }
+
+    public int hash(String s) {
+        byte[] md5 = digester.digest(Utf8.toBytes(s));
+        int hash = 0;
+        assert (md5.length == 16);
+
+        //produce an int by using only the 32 lsb:
+        int byte1 = (((int) md5[12]) << 24) & 0xFF000000;
+        int byte2 = (((int) md5[13]) << 16) & 0x00FF0000;
+        int byte3 = (((int) md5[14]) << 8) & 0x0000FF00;
+        int byte4 = (((int) md5[15])) & 0x000000FF;
+
+        hash |= byte1;
+        hash |= byte2;
+        hash |= byte3;
+        hash |= byte4;
+        return hash;
+    }
+
+    public byte[] hashFull(String s) {
+        return digester.digest(Utf8.toBytes(s));
+    }
+}