Package com.yahoo.collections

Class BobHash

java.lang.Object
com.yahoo.collections.BobHash
public class BobHash extends Object
A Java port of Michael Susag's BobHash in FastLib. This version is specifically done to be bit compatible with the one in FastLib, as it is used in decoding packets from FastServer. Hash function based on http://burtleburtle.net/bob/hash/index.html by Bob Jenkins, 1996. [email protected]. You may use this code any way you wish, private, educational, or commercial. It's free.
Author:
Michael Susag, Steinar Knutsen

  • Constructor Summary

    Constructors
    Constructor
    Description
    BobHash()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    static int
    hash(byte[] k, int initval)
    The hash function
    static int
    hash(String key)
    Hashes a string, by calling hash(byte[] key,int initval) with the utf-8 bytes of the string as key and 0 as initval.

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • BobHash

      public BobHash()

  • Method Details

    • hash

      public static int hash(String key)
      Hashes a string, by calling hash(byte[] key,int initval) with the utf-8 bytes of the string as key and 0 as initval. Note: This is copying the string content, change implementation to use efficiently on large strings. bratseth

    • hash

      public static int hash(byte[] k, int initval)
      The hash function

      hash() -- hash a variable-length key into a 32-bit value
      k : the key (the unaligned variable-length array of bytes)
      len : the length of the key, counting by bytes
      initval : can be any 4-byte value

      Returns a 32-bit value. Every bit of the key affects every bit of the return value. Every 1-bit and 2-bit delta achieves avalanche. About 6*len+35 instructions.

      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 (ub1 **)k, do it like this: for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);

      By Bob Jenkins, 1996. [email protected]. You may use this code any way you wish, private, educational, or commercial. It's free.

      See http://burtleburtle.net/bob/hash/evahash.html Use for hash table lookup, or anything where one collision in 2^^32 is acceptable. Do NOT use for cryptographic purposes.

      Parameters:
      k - the key
      initval - the previous hash, or an arbitrary value
      Returns:
      A 32 bit hash value