org.apache.hadoop.hbase.util
Class JenkinsHash
java.lang.Object
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.
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 |
JenkinsHash
public JenkinsHash()
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 hashinitval
- 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