net.spy.memcached.HashAlgorithm Maven / Gradle / Ivy
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package net.spy.memcached;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.zip.CRC32;
/**
* Known hashing algorithms for locating a server for a key.
* Note that all hash algorithms return 64-bits of hash, but only the lower
* 32-bits are significant. This allows a positive 32-bit number to be
* returned for all cases.
*/
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 fnv comparisons
* @see fnv at wikipedia
*/
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;
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;
private static MessageDigest MD5_DIGEST = null;
static {
try {
MD5_DIGEST = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException("MD5 not supported", e);
}
}
/**
* Compute the hash for the given key.
*
* @return a positive integer hash
*/
public long hash(final String k) {
long rv = 0;
int len = k.length();
switch (this) {
case NATIVE_HASH:
rv = k.hashCode();
break;
case CRC32_HASH:
// return (crc32(shift) >> 16) & 0x7fff;
CRC32 crc32 = new CRC32();
crc32.update(KeyUtil.getKeyBytes(k));
rv = (crc32.getValue() >> 16) & 0x7fff;
break;
case FNV1_64_HASH:
// Thanks to [email protected] for the pointer
rv = FNV_64_INIT;
for (int i = 0; i < len; i++) {
rv *= FNV_64_PRIME;
rv ^= k.charAt(i);
}
break;
case FNV1A_64_HASH:
rv = FNV_64_INIT;
for (int i = 0; i < len; i++) {
rv ^= k.charAt(i);
rv *= FNV_64_PRIME;
}
break;
case FNV1_32_HASH:
rv = FNV_32_INIT;
for (int i = 0; i < len; i++) {
rv *= FNV_32_PRIME;
rv ^= k.charAt(i);
}
break;
case FNV1A_32_HASH:
rv = FNV_32_INIT;
for (int i = 0; i < len; i++) {
rv ^= k.charAt(i);
rv *= FNV_32_PRIME;
}
break;
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;
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) MD5_DIGEST.clone();
} catch (CloneNotSupportedException e) {
throw new RuntimeException("clone of MD5 not supported", e);
}
md5.update(KeyUtil.getKeyBytes(k));
return md5.digest();
}
}