JenkinsHash.java
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- /**
- * Copyright 2007 The Apache Software Foundation
- *
- * 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.FileInputStream;
- import java.io.IOException;
- /**
- * 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>
- */
- 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.
- */
- @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
- */
- public static void main(String[] args) throws IOException {
- if (args.length != 1) {
- System.err.println("Usage: JenkinsHash filename");
- System.exit(-1);
- }
- FileInputStream in = new FileInputStream(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));
- }
- }