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java.lang.Objectorg.apache.hadoop.hbase.util.JenkinsHash
public class JenkinsHash
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.
Constructor Summary | |
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JenkinsHash()
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Method Summary | |
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static int |
hash(byte[] bytes)
Alternate form for hashing an entire byte array |
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 |
static void |
main(String[] args)
Compute the hash of the specified file |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
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public JenkinsHash()
Method Detail |
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public static int hash(byte[] bytes)
bytes
-
public static int hash(byte[] bytes, int initval)
bytes
- initval
-
public static int hash(byte[] key, int nbytes, int initval)
key
- the key (the unaligned variable-length array of bytes)nbytes
- number of bytes to include in hashinitval
- can be any integer value
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.
public static void main(String[] args) throws IOException
args
- name of file to compute hash of.
IOException
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