Class JenkinsHash

  extended by org.apache.hadoop.util.hash.Hash
      extended by org.apache.hadoop.util.hash.JenkinsHash

public class JenkinsHash
extends Hash

Produces 32-bit hash for hash table lookup.

lookup3.c, by Bob Jenkins, May 2006, Public Domain.

 You can use this free for any purpose.  It's in the public domain.
 It has no warranty.

See Also:
lookup3.c, Hash Functions (and how this function compares to others such as CRC, MD?, etc, Has update on the Dr. Dobbs Article

Field Summary
Fields inherited from class org.apache.hadoop.util.hash.Hash
Constructor Summary
Method Summary
static Hash getInstance()
 int hash(byte[] key, int nbytes, int initval)
          taken from hashlittle() -- hash a variable-length key into a 32-bit value
static void main(String[] args)
          Compute the hash of the specified file
Methods inherited from class org.apache.hadoop.util.hash.Hash
getHashType, getInstance, getInstance, hash, hash, parseHashType
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail


public JenkinsHash()
Method Detail


public static Hash getInstance()


public int hash(byte[] key,
                int nbytes,
                int initval)
taken from hashlittle() -- hash a variable-length key into a 32-bit value

Specified by:
hash in class Hash
key - the key (the unaligned variable-length array of bytes)
nbytes - number of bytes to include in hash
initval - can be any integer value
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. 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.


public static void main(String[] args)
                 throws IOException
Compute the hash of the specified file

args - name of file to compute hash of.

Copyright © 2009 The Apache Software Foundation