mysql fnv64函数_把string映射到64位的hashcode值方法

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#mysql fnv64函数

本文详细介绍了xMemcached中使用的多种哈希算法实现，包括原生哈希、CRC32、FNV系列、Ketama等算法，并提供了具体的Java源代码示例。

可以参考

xmemcached 的实现，源码如下：

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, but is mostly likely

* significantly slower.

CRC32_HASH,

/**

* FNV hashes are designed to be fast while maintaining a low collision

* rate. The FNV speed allows one to quickly hash lots of data while

* maintaining a reasonable collision rate.

* @see http://www.isthe.com/chongo/tech/comp/fnv/

* @see http://en.wikipedia.org/wiki/Fowler_Noll_Vo_hash

FNV1_64_HASH,

/**

* Variation of FNV.

FNV1A_64_HASH,

/**

* 32-bit FNV1.

FNV1_32_HASH,

/**

* 32-bit FNV1a.

FNV1A_32_HASH,

/**

* MD5-based hash algorithm used by ketama.

KETAMA_HASH,

/**

* From mysql source

MYSQL_HASH,

ELF_HASH,

RS_HASH,

/**

* From lua source,it is used for long key

LUA_HASH,

ELECTION_HASH,

/**

* The Jenkins One-at-a-time hash ,please see

* http://www.burtleburtle.net/bob/hash/doobs.html

ONE_AT_A_TIME;

private static final long FNV_64_INIT = 0xcbf29ce484222325L;

private static final long FNV_64_PRIME = 0x100000001b3L;

private static final long FNV_32_INIT = 2166136261L;

private static final long FNV_32_PRIME = 16777619;

/**

* Compute the hash for the given key.

* @return a positive integer hash

public long hash(final String k) {

long 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(ByteUtils.getBytes(k));

rv = crc32.getValue() >> 16 & 0x7fff;

break;

case FNV1_64_HASH: {

// Thanks to pierre@demartines.com for the pointer

rv = FNV_64_INIT;

int len = k.length();

for (int i = 0; i < len; i++) {

rv *= FNV_64_PRIME;

rv ^= k.charAt(i);

}

break;

case FNV1A_64_HASH: {

rv = FNV_64_INIT;

int len = k.length();

for (int i = 0; i < len; i++) {

rv ^= k.charAt(i);

rv *= FNV_64_PRIME;

}

break;

case FNV1_32_HASH: {

rv = FNV_32_INIT;

int len = k.length();

for (int i = 0; i < len; i++) {

rv *= FNV_32_PRIME;

rv ^= k.charAt(i);

}

break;

case FNV1A_32_HASH: {

rv = FNV_32_INIT;

int len = k.length();

for (int i = 0; i < len; i++) {

rv ^= k.charAt(i);

rv *= FNV_32_PRIME;

}

break;

case ELECTION_HASH:

case KETAMA_HASH:

byte[] bKey = computeMd5(k);

rv = (long) (bKey[3] & 0xFF) << 24 | (long) (bKey[2] & 0xFF) << 16

| (long) (bKey[1] & 0xFF) << 8 | bKey[0] & 0xFF;

break;

case MYSQL_HASH:

int nr2 = 4;

for (int i = 0; i < k.length(); i++) {

rv ^= ((rv & 63) + nr2) * k.charAt(i) + (rv << 8);

nr2 += 3;

}

break;

case ELF_HASH:

long x = 0;

for (int i = 0; i < k.length(); i++) {

rv = (rv << 4) + k.charAt(i);

if ((x = rv & 0xF0000000L) != 0) {

rv ^= x >> 24;

rv &= ~x;

}

rv = rv & 0x7FFFFFFF;

break;

case RS_HASH:

long b = 378551;

long a = 63689;

for (int i = 0; i < k.length(); i++) {

rv = rv * a + k.charAt(i);

a *= b;

}

rv = rv & 0x7FFFFFFF;

break;

case LUA_HASH:

int step = (k.length() >> 5) + 1;

rv = k.length();

for (int len = k.length(); len >= step; len -= step) {

rv = rv ^ (rv << 5) + (rv >> 2) + k.charAt(len - 1);

}

case ONE_AT_A_TIME:

try {

int hash = 0;

for (byte bt : k.getBytes("utf-8")) {

hash += (bt & 0xFF);

hash += (hash << 10);

hash ^= (hash >>> 6);

}

hash += (hash << 3);

hash ^= (hash >>> 11);

hash += (hash << 15);

return hash;

} catch (UnsupportedEncodingException e) {

throw new IllegalStateException("Hash function error", e);

}

default:

assert false;

}

return rv & 0xffffffffL; /* Truncate to 32-bits */

}

/**

* Get the md5 of the given key.

public static byte[] computeMd5(String k) {

MessageDigest md5;

try {

md5 = MessageDigest.getInstance("MD5");

} catch (NoSuchAlgorithmException e) {

throw new RuntimeException("MD5 not supported", e);

}

md5.reset();

md5.update(ByteUtils.getBytes(k));

return md5.digest();

}

// public static void main(String[] args) {

// HashAlgorithm alg=HashAlgorithm.CRC32_HASH;

// long h=0;

// long start=System.currentTimeMillis();

// for(int i=0;i<100000;i++)

// h=alg.hash("MYSQL_HASH");

// System.out.println(System.currentTimeMillis()-start);

// }

}

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2012-08-21 16:59