/[Apache-SVN]/hadoop/hbase/trunk/src/java/org/apache/hadoop/hbase/util/JenkinsHash.java
ViewVC logotype

Diff of /hadoop/hbase/trunk/src/java/org/apache/hadoop/hbase/util/JenkinsHash.java

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 639775, Fri Mar 21 19:46:34 2008 UTC revision 656868, Thu May 15 22:10:47 2008 UTC
# Line 24  import java.io.FileInputStream; Line 24  import java.io.FileInputStream;
24  import java.io.IOException;  import java.io.IOException;
25    
26  /**  /**
27   * lookup3.c, by Bob Jenkins, May 2006, Public Domain.   * Produces 32-bit hash for hash table lookup.
28   * <a href="http://burtleburtle.net/bob/c/lookup3.c">lookup3.c</a>   *
29     * <pre>lookup3.c, by Bob Jenkins, May 2006, Public Domain.
30   *   *
31   * You can use this free for any purpose.  It's in the public domain.   * You can use this free for any purpose.  It's in the public domain.
32   * It has no warranty.   * It has no warranty.
33     * </pre>
34   *   *
35   * Produces 32-bit hash for hash table lookup.   * @see <a href="http://burtleburtle.net/bob/c/lookup3.c">lookup3.c</a>
36     * @see <a href="http://www.ddj.com/184410284">Hash Functions (and how this
37     * function compares to others such as CRC, MD?, etc</a>
38     * @see <a href="http://burtleburtle.net/bob/hash/doobs.html">Has update on the
39     * Dr. Dobbs Article</a>
40   */   */
41  public class JenkinsHash {  public class JenkinsHash {
42    private static long INT_MASK  = 0x00000000ffffffffL;    private static long INT_MASK  = 0x00000000ffffffffL;
# Line 45  public class JenkinsHash { Line 51  public class JenkinsHash {
51     * Alternate form for hashing an entire byte array     * Alternate form for hashing an entire byte array
52     *     *
53     * @param bytes     * @param bytes
54       * @return hash value
55       */
56      public static int hash(byte[] bytes) {
57        return hash(bytes, bytes.length, -1);
58      }
59    
60      /**
61       * Alternate form for hashing an entire byte array
62       *
63       * @param bytes
64     * @param initval     * @param initval
65     * @return hash value     * @return hash value
66     */     */
# Line 62  public class JenkinsHash { Line 78  public class JenkinsHash {
78     * return value.  Two keys differing by one or two bits will have totally     * return value.  Two keys differing by one or two bits will have totally
79     * different hash values.     * different hash values.
80     *     *
81     * The best hash table sizes are powers of 2.  There is no need to do mod a     * <p>The best hash table sizes are powers of 2.  There is no need to do mod
82     * prime (mod is sooo slow!).  If you need less than 32 bits, use a bitmask.     * a prime (mod is sooo slow!).  If you need less than 32 bits, use a bitmask.
83     * For example, if you need only 10 bits, do h = (h & hashmask(10));     * For example, if you need only 10 bits, do
84       * <code>h = (h & hashmask(10));</code>
85     * In which case, the hash table should have hashsize(10) elements.     * In which case, the hash table should have hashsize(10) elements.
86     *     *
87     * If you are hashing n strings byte[][] k, do it like this:     * <p>If you are hashing n strings byte[][] k, do it like this:
88     * for (int i = 0, h = 0; i < n; ++i) h = hash( k[i], h);     * for (int i = 0, h = 0; i < n; ++i) h = hash( k[i], h);
89     *     *
90     * By Bob Jenkins, 2006.  bob_jenkins@burtleburtle.net.  You may use this     * <p>By Bob Jenkins, 2006.  bob_jenkins@burtleburtle.net.  You may use this
91     * code any way you wish, private, educational, or commercial.  It's free.     * code any way you wish, private, educational, or commercial.  It's free.
92     *     *
93     * Use for hash table lookup, or anything where one collision in 2^^32 is     * <p>Use for hash table lookup, or anything where one collision in 2^^32 is
94     * acceptable.  Do NOT use for cryptographic purposes.     * acceptable.  Do NOT use for cryptographic purposes.
95    */    */
96    public static int hash(byte[] key, int nbytes, int initval) {    public static int hash(byte[] key, int nbytes, int initval) {
Legend:
Removed from v.639775  
changed lines
  Added in v.656868
apache@apache.org
 ViewVC Help
Powered by ViewVC 1.1.2