Use lookup table when calculating CRC16 XMODEM

* I borrowed it from b921931480

src/test/java/redis/clients/jedis/tests/benchmark/CRC16Benchmark.java

@@ -0,0 +1,27 @@
+package redis.clients.jedis.tests.benchmark;
+
+import java.util.Calendar;
+
+import redis.clients.util.JedisClusterCRC16;
+
+public class CRC16Benchmark {
+    private static final int TOTAL_OPERATIONS = 10000000;
+
+    private static String[] TEST_SET = {
+	"", "123456789", "sfger132515", "hae9Napahngaikeethievubaibogiech", 
+	"AAAAAAAAAAAAAAAAAAAAAA", "Hello, World!"
+    };
+    
+    public static void main(String[] args) {
+	long begin = Calendar.getInstance().getTimeInMillis();
+
+	for (int n = 0; n <= TOTAL_OPERATIONS; n++) {
+	    JedisClusterCRC16.getSlot(TEST_SET[n % TEST_SET.length]);
+	}
+
+	long elapsed = Calendar.getInstance().getTimeInMillis() - begin;
+
+	System.out.println(((1000 * TOTAL_OPERATIONS) / elapsed) + " ops");
+    }
+    
+}

src/test/java/redis/clients/jedis/tests/utils/JedisClusterCRC16Test.java

@@ -0,0 +1,43 @@
+package redis.clients.jedis.tests.utils;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+
+import org.junit.Test;
+
+import redis.clients.util.JedisClusterCRC16;
+
+public class JedisClusterCRC16Test {
+
+    @Test
+    public void testGetCRC16() throws Exception {
+	Map<String, Integer> solutions = prepareSolutionSet();
+	
+	for (Entry<String, Integer> entry : solutions.entrySet()) {
+	    // string version
+	    assertEquals(entry.getValue().intValue(), JedisClusterCRC16.getCRC16(entry.getKey()));
+	    
+	    // byte array version
+	    assertEquals(entry.getValue().intValue(), JedisClusterCRC16.getCRC16(entry.getKey().getBytes()));
+	}
+    }
+    
+    @Test
+    public void testGetSlot() {
+	assertEquals(7186, JedisClusterCRC16.getSlot("51"));
+    }
+
+    private Map<String, Integer> prepareSolutionSet() {
+	Map<String, Integer> solutionMap = new HashMap<String, Integer>();
+	solutionMap.put("", 0x0);
+	solutionMap.put("123456789", 0x31C3);
+	solutionMap.put("sfger132515", 0xA45C);
+	solutionMap.put("hae9Napahngaikeethievubaibogiech", 0x58CE);
+	solutionMap.put("AAAAAAAAAAAAAAAAAAAAAA", 0x92cd);
+	solutionMap.put("Hello, World!", 0x4FD6);
+	return solutionMap;
+    }
+}