org.apache.activemq.util

Class JenkinsHash

java.lang.Object

org.apache.activemq.util.JenkinsHash

public class JenkinsHash
extends Object

Constructor Summary

Constructors

Constructor and Description
JenkinsHash()

Method Summary

Modifier and Type	Method and Description
static JenkinsHash	getInstance()
int	hash(byte[] bytes) Calculate a hash using all bytes from the input argument, and a seed of -1.
int	hash(byte[] bytes, int initVal) Calculate a hash using all bytes from the input argument, and a seed of -1.
int	hash(byte[] key, int nbytes, int initval) taken from hashlittle() -- hash a variable-length key into a 32-bit value

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

JenkinsHash

public JenkinsHash()

Method Detail

getInstance

public static JenkinsHash getInstance()

hash

public int hash(byte[] bytes)

Calculate a hash using all bytes from the input argument, and a seed of -1.

Parameters:

bytes - input bytes

Returns:

hash value

hash

public int hash(byte[] bytes,
                int initVal)

Calculate a hash using all bytes from the input argument, and a seed of -1.

Parameters:

bytes - input bytes

Returns:

hash value

hash

public int hash(byte[] key,
                int nbytes,
                int initval)

taken from hashlittle() -- hash a variable-length key into a 32-bit value

Parameters:

key - the key (the unaligned variable-length array of bytes)

nbytes - number of bytes to include in hash

initval - can be any integer value

Returns:

a 32-bit value. Every bit of the key affects every bit of the return value. Two keys differing by one or two bits will have totally different hash values.

The best hash table sizes are powers of 2. There is no need to do mod a prime (mod is sooo slow!). If you need less than 32 bits, use a bitmask. For example, if you need only 10 bits, do h = (h & hashmask(10)); In which case, the hash table should have hashsize(10) elements.

If you are hashing n strings byte[][] k, do it like this: for (int i = 0, h = 0; i < n; ++i) h = hash( k[i], h);

By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this code any way you wish, private, educational, or commercial. It's free.

Use for hash table lookup, or anything where one collision in 2^^32 is acceptable. Do NOT use for cryptographic purposes.