uk.co.thomasc.steamkit.util.classlesshasher

Class JenkinsHash

java.lang.Object

uk.co.thomasc.steamkit.util.classlesshasher.JenkinsHash

public class JenkinsHash
extends Object

Hash algorithm by Bob Jenkins, 1996. You may use this code any way you wish, private, educational, or commercial. It's free. See: http://burtleburtle.net/bob/hash/doobs.html Use for hash table lookup, or anything where one collision in 2^^32 is acceptable. Do NOT use for cryptographic purposes. Java port by Gray Watson http://256.com/gray/

Field Summary

Fields

Modifier and Type	Field and Description
(package private) long	a
(package private) long	b
(package private) long	c
private static long	MAX_VALUE

Constructor Summary

Constructors

Constructor and Description
JenkinsHash()

Method Summary

Methods

Modifier and Type	Method and Description
private long	add(long val, long add) Do addition and turn into 4 bytes.
private long	byteToLong(byte b) Convert a byte into a long value without making it negative.
private long	fourByteToLong(byte[] bytes, int offset) Convert 4 bytes from the buffer at offset into a long value.
long	hash(byte[] buffer) See hash(byte[] buffer, long initialValue)
long	hash(byte[] buffer, long initialValue) Hash a variable-length key into a 32-bit value.
private void	hashMix() Mix up the values in the hash function.
private long	leftShift(long val, int shift) Left shift val by shift bits.
private long	subtract(long val, long subtract) Do subtraction and turn into 4 bytes.
private long	xor(long val, long xor) Left shift val by shift bits and turn in 4 bytes.

Methods inherited from class java.lang.Object

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

Field Detail

MAX_VALUE

private static final long MAX_VALUE

See Also:

Constant Field Values

a

long a

b

long b

c

long c

Constructor Detail

JenkinsHash

public JenkinsHash()

Method Detail

byteToLong

private long byteToLong(byte b)

Convert a byte into a long value without making it negative.

add

private long add(long val,
       long add)

Do addition and turn into 4 bytes.

subtract

private long subtract(long val,
            long subtract)

Do subtraction and turn into 4 bytes.

xor

private long xor(long val,
       long xor)

Left shift val by shift bits and turn in 4 bytes.

leftShift

private long leftShift(long val,
             int shift)

Left shift val by shift bits. Cut down to 4 bytes.

fourByteToLong

private long fourByteToLong(byte[] bytes,
                  int offset)

Convert 4 bytes from the buffer at offset into a long value.

hashMix

private void hashMix()

Mix up the values in the hash function.

hash

public long hash(byte[] buffer,
        long initialValue)

Hash a variable-length key into 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. The best hash table sizes are powers of 2.

Parameters:

buffer - Byte array that we are hashing on.

initialValue - Initial value of the hash if we are continuing from a previous run. 0 if none.

Returns:

Hash value for the buffer.

hash

public long hash(byte[] buffer)

See hash(byte[] buffer, long initialValue)

Parameters:

buffer - Byte array that we are hashing on.

Returns:

Hash value for the buffer.