Support more than one hashing algorithm.

	Tested the crc32 hash algorithm against values returned from the perl
client's implementation.

src/java/net/spy/memcached/HashAlgorithm.java

@@ -0,0 +1,40 @@
+package net.spy.memcached;
+
+import java.util.zip.CRC32;
+
+/**
+ * Known hashing algorithms for locating a server for a key.
+ */
+public enum HashAlgorithm {
+	/**
+	 * Native hash (String.hashCode()).
+	 */
+	NATIVE_HASH,
+	/**
+	 * CRC32_HASH as used by the perl API.  This will be more consistent
+	 * both across multiple API users as well as java versions.
+	 */
+	CRC32_HASH;
+
+	/**
+	 * Compute the hash for the given key.
+	 * @return a positive integer hash
+	 */
+	public int hash(String k) {
+		int rv=0;
+		switch(this) {
+			case NATIVE_HASH:
+				rv=k.hashCode();
+				break;
+			case CRC32_HASH:
+				// return (crc32(shift) >> 16) & 0x7fff;
+				CRC32 crc32=new CRC32();
+				crc32.update(k.getBytes());
+				rv=(int)(crc32.getValue() & 0xffffffff);
+				rv=(rv >> 16) & 0x7fff;
+				break;
+			default: assert false;
+		}
+		return Math.abs(rv);
+	}
+}

src/java/net/spy/memcached/MemcachedClient.java

@@ -75,6 +75,7 @@ public class MemcachedClient extends SpyThread {
 
 	private volatile boolean running=true;
 	private MemcachedConnection conn=null;
+	private HashAlgorithm hashAlg=HashAlgorithm.NATIVE_HASH;
 	Transcoder transcoder=null;
 
 	/** 
@@ -98,6 +99,20 @@ public MemcachedClient(InetSocketAddress... ia) throws IOException {
 		start();
 	}
 
+	/**
+	 * Set the hash algorithm.
+	 */
+	public HashAlgorithm getHashAlgorithm() {
+		return hashAlg;
+	}
+
+	public void setHashAlgorithm(HashAlgorithm to) {
+		if(to == null) {
+			throw new NullPointerException("Null hash algorithm not allowed");
+		}
+		hashAlg=to;
+	}
+
 	/**
 	 * Set the transcoder for managing the cache representations of objects
 	 * going in and out of the cache.
@@ -509,7 +524,7 @@ private int getServerForKey(String key) {
 			throw new IllegalArgumentException(
 					"Key contains invalid characters: " + key);
 		}
-		int rv=Math.abs(key.hashCode()) % conn.getNumConnections();
+		int rv=hashAlg.hash(key) % conn.getNumConnections();
 		assert rv >= 0 : "Returned negative key for key " + key;
 		assert rv < conn.getNumConnections()
 			: "Invalid server number " + rv + " for key " + key;

src/test/net/spy/memcached/HashAlgorithmTest.java

@@ -0,0 +1,41 @@
+package net.spy.memcached;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import junit.framework.TestCase;
+
+/**
+ * Test the hash algorithms.
+ */
+public class HashAlgorithmTest extends TestCase {
+
+	private void assertHash(HashAlgorithm ha, String key, int exp) {
+		assertTrue(exp >= 0);
+		assertEquals("Invalid " + ha + " for key " + key, exp, ha.hash(key));
+		// System.out.println(ha + "(" + key + ") = " + exp);
+	}
+
+	// I don't hardcode any values here because they're subject to change
+	private void assertNativeHash(String key) {
+		assertHash(HashAlgorithm.NATIVE_HASH, key, Math.abs(key.hashCode())); 
+	}
+
+	public void testNativeHash() {
+		for(String k : new String[]{"Test1", "Test2", "Test3", "Test4"}) {
+			assertNativeHash(k);
+		}
+	}
+
+	public void testCrc32Hash() {
+		Map<String, Integer> exp=new HashMap<String, Integer>();
+		exp.put("Test1", 19315);
+		exp.put("Test2", 21114);
+		exp.put("Test3", 9597);
+		exp.put("Test4", 15129);
+
+		for(Map.Entry<String, Integer> me : exp.entrySet()) {
+			assertHash(HashAlgorithm.CRC32_HASH, me.getKey(), me.getValue());
+		}
+	}
+}