java CRC16算法，分解一个大Key实例。相关hash算法代码

package org.rui.hi;

/**
* 测试： 解决场景:把1亿的用户 存储在一个队列里，过大。用sharding 摸拟redis 集群 sharding Redis
* 集群使用数据分片（sharding）而非一致性哈希（consistency hashing）来实现： 一个 Redis 集群包含 16384
* 个哈希槽（hash slot）， 数据库中的每个键都属于这 16384 个哈希槽的其中一个， 集群使用公式 CRC16(key) % 16384 来计算键
* key 属于哪个槽， 其中 CRC16(key) 语句用于计算键 key 的 CRC16 校验和 。
*
* @author ruiliang
*
*/
public class HashDist {
public final static int maxInt = 1000;// 00000;//1亿
public final static int USER_KEY_SLOT_COUNT = 20; // 定议分配存储用户的Slot位
// ，如果存储有压力，可调大槽位

public static void main(String[] args) {

// int 不用crc16
for (int i = 1; i < maxInt; i++) {
// 根据玩家id 分布指定到Slot位
int ranint = i % USER_KEY_SLOT_COUNT;
String key = "key:" + ranint;
System.out.println("key:" + key);
// redisList.lpush(randomKey, String.valueOf(playerId));
}

/**
* crc16 redis 集群也是用这种方式分配key
*/

String a = "a,b,c,d,e,f,g,g,g";
for (String j : a.split(",")) {
int solt = CRCJava.crc16(j.getBytes()) % USER_KEY_SLOT_COUNT;
String key = "key:" + solt;
System.out.println("crc%solt=key:" + key);
}

// redisList.lpush(randomKey, String.valueOf(playerId));

}

}
/**
* output: ...
*
* key:key:0 key:key:1 key:key:2 key:key:3 key:key:4 key:key:5 key:key:6
* key:key:7 key:key:8 key:key:9 key:key:10 key:key:11 key:key:12 key:key:13
* key:key:14 key:key:15 key:key:16 key:key:17 key:key:18 key:key:19 key:key:0
* key:key:1 key:key:2 key:key:3 key:key:4 key:key:5 key:key:6 key:key:7
* key:key:8 key:key:9 key:key:10 key:key:11 key:key:12 key:key:13 key:key:14
* key:key:15 key:key:16 key:key:17 key:key:18 key:key:19 key:key:0 key:key:1
* key:key:2 key:key:3 key:key:4 key:key:5 key:key:6 key:key:7 key:key:8
* key:key:9 key:key:10 key:key:11 key:key:12 key:key:13 key:key:14 key:key:15
* key:key:16 key:key:17 key:key:18 key:key:19 key:key:0 key:key:1 key:key:2
* key:key:3 key:key:4 key:key:5 key:key:6 key:key:7 key:key:8 key:key:9
* key:key:10 key:key:11 key:key:12 key:key:13 key:key:14 key:key:15 key:key:16
* key:key:17 key:key:18 key:key:19 key:key:0 key:key:1 key:key:2 key:key:3
* key:key:4 key:key:5 key:key:6 key:key:7 key:key:8 key:key:9 key:key:10
* key:key:11 key:key:12 key:key:13 key:key:14 key:key:15 key:key:16 key:key:17
* key:key:18 key:key:19 key:key:0 key:key:1 key:key:2 key:key:3 key:key:4
* key:key:5 key:key:6 key:key:7 key:key:8 key:key:9 key:key:10 key:key:11
* key:key:12 key:key:13 key:key:14 key:key:15 key:key:16 key:key:17 key:key:18
* key:key:19 crc%solt=key:key:11 crc%solt=key:key:8 crc%solt=key:key:17
* crc%solt=key:key:10 crc%solt=key:key:19 crc%solt=key:key:16
* crc%solt=key:key:5 crc%solt=key:key:5 crc%solt=key:key:5
*/

package org.rui.hi;

public class CRCJava {

public static void main(String[] args) {
String a = "a,b,c,d,e,f,g";

for (String i : a.split(",")) {
System.out.println(crc16(i.getBytes()));
}
System.out.println("----------------------------------");
for (String i : a.split(",")) {
System.out.println(crc162(i.getBytes()));
}

}

/******************************************************************************
* Compilation: javac CRC16CCITT.java Execution: java CRC16CCITT s
* Dependencies:
*
* Reads in a sequence of bytes and prints out its 16 bit Cylcic Redundancy
* Check (CRC-CCIIT 0xFFFF).
*
* 1 + x + x^5 + x^12 + x^16 is irreducible polynomial.
*
* % java CRC16-CCITT 123456789 CRC16-CCITT = 29b1
*
******************************************************************************/

public static int crc16(final byte[] buffer) {

int crc = 0xFFFF; // initial value 65535
int polynomial = 0x1021; // 0001 0000 0010 0001 (0, 5, 12)
// byte[] testBytes = "123456789".getBytes("ASCII");
for (byte b : buffer) {
for (int i = 0; i < 8; i++) {
boolean bit = ((b >> (7 - i) & 1) == 1);
boolean c15 = ((crc >> 15 & 1) == 1);
crc <<= 1;
if (c15 ^ bit)
crc ^= polynomial;
}
}

return crc &= 0xffff;

}

/**
*
* @param buffer
* @return
*/
static int crc162(final byte[] buffer) {
int crc = 0xFFFF;

for (int j = 0; j < buffer.length; j++) {
crc = ((crc >>> 8) | (crc << 8)) & 0xffff;
crc ^= (buffer[j] & 0xff);// byte to int, trunc sign
crc ^= ((crc & 0xff) >> 4);
crc ^= (crc << 12) & 0xffff;
crc ^= ((crc & 0xFF) << 5) & 0xffff;
}
crc &= 0xffff;
return crc;

}
}


---------------------------------------
各种hash算法

package org.rui.hi;

/**
* 相关hash算法
*
* @author ruiliang
*
*/
public class HashTest {

public static void main(String[] args) {

// long hash = DEKHash("123456");
// System.out.println(hash);
System.out.println(hashCode(0));
System.out.println(hashCode(1));
System.out.println(hashCode(2));
System.out.println(hashCode(3));
System.out.println(hashCode(123456));
System.out.println(hashCode(123457));
System.out.println(hashCode(123458));

System.out.println(PJWHash("0"));
System.out.println(PJWHash("1"));
System.out.println(PJWHash("2"));
System.out.println(PJWHash("3"));
System.out.println(PJWHash("123456"));
System.out.println(PJWHash("123457"));
System.out.println(PJWHash("123458"));

}

/**
* 从Robert Sedgwicks的 Algorithms in C一书中得到了
*
* @param str
* @return
*/
public static long RSHash(String str) {
int b = 378551;
int a = 63689;
long hash = 0;
for (int i = 0; i < str.length(); i++) {
hash = hash * a + str.charAt(i);
a = a * b;
}
return hash;
}

/**
* Justin Sobel写的一个位操作的哈希函数。
*
* @param str
* @return
*/
public static long JSHash(String str) {
long hash = 1315423911;
for (int i = 0; i < str.length(); i++) {
hash ^= ((hash << 5) + str.charAt(i) + (hash >> 2));
}
return hash;
}

/**
* PJW 该散列算法是基于贝尔实验室的彼得J温伯格的的研究。在Compilers一书中（原则，技术和工具），建议采用这个算法的散列函数的哈希方法。
*
* @param str
* @return
*/
public static long PJWHash(String str) {
long BitsInUnsignedInt = (long) (4 * 8);
long ThreeQuarters = (long) ((BitsInUnsignedInt * 3) / 4);
long OneEighth = (long) (BitsInUnsignedInt / 8);
long HighBits = (long) (0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth);
long hash = 0;
long test = 0;
for (int i = 0; i < str.length(); i++) {
hash = (hash << OneEighth) + str.charAt(i);
if ((test = hash & HighBits) != 0) {
hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));
}
}
return hash;
}

/**
* ELF 和PJW很相似，在Unix系统中使用的较多。
*
* @param str
* @return
*/
public static long ELFHash(String str) {
long hash = 0;
long x = 0;
for (int i = 0; i < str.length(); i++) {
hash = (hash << 4) + str.charAt(i);
if ((x = hash & 0xF0000000L) != 0) {
hash ^= (x >> 24);
}
hash &= ~x;
}
return hash;
}

/**
* BKDR 这个算法来自Brian Kernighan 和 Dennis Ritchie的 The C Programming
* Language。这是一个很简单的哈希算法,使用了一系列奇怪的数字,形式如31,3131,31...31,看上去和DJB算法很相似。
*
* @param str
* @return
*/

public static long BKDRHash(String str) {
long seed = 131; // 31 131 1313 13131 131313 etc..
long hash = 0;
for (int i = 0; i < str.length(); i++) {
hash = (hash * seed) + str.charAt(i);
}
return hash;
}

public static long SDBMHash(String str) {
long hash = 0;
for (int i = 0; i < str.length(); i++) {
hash = str.charAt(i) + (hash << 6) + (hash << 16) - hash;
}
return hash;
}

/**
* DJB 这个算法是Daniel J.Bernstein 教授发明的，是目前公布的最有效的哈希函数。
*
* @param str
* @return
*/
public static long DJBHash(String str) {
long hash = 5381;
for (int i = 0; i < str.length(); i++) {
hash = ((hash << 5) + hash) + str.charAt(i);
}
return hash;
}

/**
* .DEK 由伟大的Knuth在《编程的艺术 第三卷》的第六章排序和搜索中给出。
*
* @param str
* @return
*/
public static long DEKHash(String str) {
long hash = str.length();
for (int i = 0; i < str.length(); i++) {
hash = ((hash << 5) ^ (hash >> 27)) ^ str.charAt(i);
}
return hash;
}

/**
* jdk hash
*
* @param a
* @return
*/
public static int hashCode(int a) {
final int prime = 48;
int result = 1;
result = prime * result + a;
return result;
}
}