JenkinsHash.java
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.util.hash;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Paths;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* Produces 32-bit hash for hash table lookup.
*
* <pre>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.
* </pre>
*
* @see <a href="http://burtleburtle.net/bob/c/lookup3.c">lookup3.c</a>
* @see <a href="http://www.ddj.com/184410284">Hash Functions (and how this
* function compares to others such as CRC, MD?, etc</a>
* @see <a href="http://burtleburtle.net/bob/hash/doobs.html">Has update on the
* Dr. Dobbs Article</a>
*/
@InterfaceAudience.Private
@InterfaceStability.Unstable
public class JenkinsHash extends Hash {
private static long INT_MASK = 0x00000000ffffffffL;
private static long BYTE_MASK = 0x00000000000000ffL;
private static JenkinsHash _instance = new JenkinsHash();
public static Hash getInstance() {
return _instance;
}
private static long rot(long val, int pos) {
return ((Integer.rotateLeft(
(int)(val & INT_MASK), pos)) & INT_MASK);
}
/**
* taken from hashlittle() -- hash a variable-length key into a 32-bit value
*
* @param key the key (the unaligned variable-length array of bytes)
* @param nbytes number of bytes to include in hash
* @param initval can be any integer value
* @return 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.
*
* <p>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
* <code>h = (h & hashmask(10));</code>
* In which case, the hash table should have hashsize(10) elements.
*
* <p>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);
*
* <p>By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
* code any way you wish, private, educational, or commercial. It's free.
*
* <p>Use for hash table lookup, or anything where one collision in 2^^32 is
* acceptable. Do NOT use for cryptographic purposes.
*/
@Override
@SuppressWarnings("fallthrough")
public int hash(byte[] key, int nbytes, int initval) {
int length = nbytes;
long a, b, c; // We use longs because we don't have unsigned ints
a = b = c = (0x00000000deadbeefL + length + initval) & INT_MASK;
int offset = 0;
for (; length > 12; offset += 12, length -= 12) {
a = (a + (key[offset + 0] & BYTE_MASK)) & INT_MASK;
a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK;
b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK;
c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
/*
* mix -- mix 3 32-bit values reversibly.
* This is reversible, so any information in (a,b,c) before mix() is
* still in (a,b,c) after mix().
*
* If four pairs of (a,b,c) inputs are run through mix(), or through
* mix() in reverse, there are at least 32 bits of the output that
* are sometimes the same for one pair and different for another pair.
*
* This was tested for:
* - pairs that differed by one bit, by two bits, in any combination
* of top bits of (a,b,c), or in any combination of bottom bits of
* (a,b,c).
* - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
* the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
* is commonly produced by subtraction) look like a single 1-bit
* difference.
* - the base values were pseudorandom, all zero but one bit set, or
* all zero plus a counter that starts at zero.
*
* Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
* satisfy this are
* 4 6 8 16 19 4
* 9 15 3 18 27 15
* 14 9 3 7 17 3
* Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing for
* "differ" defined as + with a one-bit base and a two-bit delta. I
* used http://burtleburtle.net/bob/hash/avalanche.html to choose
* the operations, constants, and arrangements of the variables.
*
* This does not achieve avalanche. There are input bits of (a,b,c)
* that fail to affect some output bits of (a,b,c), especially of a.
* The most thoroughly mixed value is c, but it doesn't really even
* achieve avalanche in c.
*
* This allows some parallelism. Read-after-writes are good at doubling
* the number of bits affected, so the goal of mixing pulls in the
* opposite direction as the goal of parallelism. I did what I could.
* Rotates seem to cost as much as shifts on every machine I could lay
* my hands on, and rotates are much kinder to the top and bottom bits,
* so I used rotates.
*
* #define mix(a,b,c) \
* { \
* a -= c; a ^= rot(c, 4); c += b; \
* b -= a; b ^= rot(a, 6); a += c; \
* c -= b; c ^= rot(b, 8); b += a; \
* a -= c; a ^= rot(c,16); c += b; \
* b -= a; b ^= rot(a,19); a += c; \
* c -= b; c ^= rot(b, 4); b += a; \
* }
*
* mix(a,b,c);
*/
a = (a - c) & INT_MASK; a ^= rot(c, 4); c = (c + b) & INT_MASK;
b = (b - a) & INT_MASK; b ^= rot(a, 6); a = (a + c) & INT_MASK;
c = (c - b) & INT_MASK; c ^= rot(b, 8); b = (b + a) & INT_MASK;
a = (a - c) & INT_MASK; a ^= rot(c,16); c = (c + b) & INT_MASK;
b = (b - a) & INT_MASK; b ^= rot(a,19); a = (a + c) & INT_MASK;
c = (c - b) & INT_MASK; c ^= rot(b, 4); b = (b + a) & INT_MASK;
}
//-------------------------------- last block: affect all 32 bits of (c)
switch (length) { // all the case statements fall through
case 12:
c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
case 11:
c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
case 10:
c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
case 9:
c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK;
case 8:
b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
case 7:
b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
case 6:
b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
case 5:
b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK;
case 4:
a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
case 3:
a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
case 2:
a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
case 1:
a = (a + (key[offset + 0] & BYTE_MASK)) & INT_MASK;
break;
case 0:
return (int)(c & INT_MASK);
}
/*
* final -- final mixing of 3 32-bit values (a,b,c) into c
*
* Pairs of (a,b,c) values differing in only a few bits will usually
* produce values of c that look totally different. This was tested for
* - pairs that differed by one bit, by two bits, in any combination
* of top bits of (a,b,c), or in any combination of bottom bits of
* (a,b,c).
*
* - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
* the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
* is commonly produced by subtraction) look like a single 1-bit
* difference.
*
* - the base values were pseudorandom, all zero but one bit set, or
* all zero plus a counter that starts at zero.
*
* These constants passed:
* 14 11 25 16 4 14 24
* 12 14 25 16 4 14 24
* and these came close:
* 4 8 15 26 3 22 24
* 10 8 15 26 3 22 24
* 11 8 15 26 3 22 24
*
* #define final(a,b,c) \
* {
* c ^= b; c -= rot(b,14); \
* a ^= c; a -= rot(c,11); \
* b ^= a; b -= rot(a,25); \
* c ^= b; c -= rot(b,16); \
* a ^= c; a -= rot(c,4); \
* b ^= a; b -= rot(a,14); \
* c ^= b; c -= rot(b,24); \
* }
*
*/
c ^= b; c = (c - rot(b,14)) & INT_MASK;
a ^= c; a = (a - rot(c,11)) & INT_MASK;
b ^= a; b = (b - rot(a,25)) & INT_MASK;
c ^= b; c = (c - rot(b,16)) & INT_MASK;
a ^= c; a = (a - rot(c,4)) & INT_MASK;
b ^= a; b = (b - rot(a,14)) & INT_MASK;
c ^= b; c = (c - rot(b,24)) & INT_MASK;
return (int)(c & INT_MASK);
}
/**
* Compute the hash of the specified file
* @param args name of file to compute hash of.
* @throws IOException raised on errors performing I/O.
*/
public static void main(String[] args) throws IOException {
if (args.length != 1) {
System.err.println("Usage: JenkinsHash filename");
System.exit(-1);
}
try (InputStream in = Files.newInputStream(Paths.get(args[0]))) {
byte[] bytes = new byte[512];
int value = 0;
JenkinsHash hash = new JenkinsHash();
for (int length = in.read(bytes); length > 0; length = in.read(bytes)) {
value = hash.hash(bytes, length, value);
}
System.out.println(Math.abs(value));
}
}
}