Package org.apache.hadoop.util.hash

Class JenkinsHash

java.lang.Object
org.apache.hadoop.util.hash.Hash
org.apache.hadoop.util.hash.JenkinsHash
@Private @Unstable 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:

  • Constructor Details

    • JenkinsHash

      public JenkinsHash()

  • Method Details

    • getInstance

      public static Hash getInstance()

    • hash

      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
      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.

    • main

      public static void main(String[] args) throws IOException
      Compute the hash of the specified file
      Parameters:
      args - name of file to compute hash of.
      Throws:
      IOException - raised on errors performing I/O.