org.apache.hadoop.hbase.util
Class JenkinsHash

java.lang.Object
  extended by org.apache.hadoop.hbase.util.JenkinsHash

public class JenkinsHash
extends Object

lookup3.c, by Bob Jenkins, May 2006, Public Domain. lookup3.c You can use this free for any purpose. It's in the public domain. It has no warranty. Produces 32-bit hash for hash table lookup.


Constructor Summary
JenkinsHash()
           
 
Method Summary
static int hash(byte[] bytes, int initval)
          Alternate form for hashing an entire byte array
static 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

hash

public static int hash(byte[] bytes,
                       int initval)
Alternate form for hashing an entire byte array

Parameters:
bytes -
initval -
Returns:
hash value

hash

public static 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.


Copyright © 2006 The Apache Software Foundation