Jenkins Hash
/*
* @(#)$Id$
*
* Copyright 2006-2008 Makoto YUI
*
* Licensed 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.
*
* Contributors:
* Makoto YUI - initial implementation
*/
//package xbird.util.hashes;
/**
* 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 final class JenkinsHash {
private static long INT_MASK = 0x00000000ffffffffL;
private static long BYTE_MASK = 0x00000000000000ffL;
public JenkinsHash() {}
public static int hash32(final byte[] key, final int initval) {
return hash32(key, key.length, initval);
}
/**
* 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.
*/
public static int hash32(final byte[] key, final int nbytes, final 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);
}
private static long rot(final long val, final int pos) {
return ((Integer.rotateLeft((int) (val & INT_MASK), pos)) & INT_MASK);
}
/*
* --------------------------------------------------------------------
* hash() -- hash a variable-length key into a 64-bit value k : the key (the
* unaligned variable-length array of bytes) level : can be any 8-byte value
* Returns a 64-bit value. Every bit of the key affects every bit of the
* return value. No funnels. Every 1-bit and 2-bit delta achieves avalanche.
* About 41+5len instructions.
*
* 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 64 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 (ub1 **)k, do it like this: for (i=0, h=0;
* i<n; ++i) h = hash( k[i], len[i], h);
*
* By Bob Jenkins, Jan 4 1997. bob_jenkins@burtleburtle.net. You may use
* this code any way you wish, private, educational, or commercial, but I
* would appreciate if you give me credit.
*
* See http://burtleburtle.net/bob/hash/evahash.html Use for hash table
* lookup, or anything where one collision in 2^^64 is acceptable. Do NOT
* use for cryptographic purposes.
* --------------------------------------------------------------------
*/
public static long hash64(final byte[] k, final long initval) {
/* Set up the internal state */
long a = initval;
long b = initval;
/* the golden ratio; an arbitrary value */
long c = 0x9e3779b97f4a7c13L;
int len = k.length;
/*---------------------------------------- handle most of the key */
int i = 0;
while(len >= 24) {
a += gatherLongLE(k, i);
b += gatherLongLE(k, i + 8);
c += gatherLongLE(k, i + 16);
/* mix64(a, b, c); */
a -= b;
a -= c;
a ^= (c >> 43);
b -= c;
b -= a;
b ^= (a << 9);
c -= a;
c -= b;
c ^= (b >> 8);
a -= b;
a -= c;
a ^= (c >> 38);
b -= c;
b -= a;
b ^= (a << 23);
c -= a;
c -= b;
c ^= (b >> 5);
a -= b;
a -= c;
a ^= (c >> 35);
b -= c;
b -= a;
b ^= (a << 49);
c -= a;
c -= b;
c ^= (b >> 11);
a -= b;
a -= c;
a ^= (c >> 12);
b -= c;
b -= a;
b ^= (a << 18);
c -= a;
c -= b;
c ^= (b >> 22);
/* mix64(a, b, c); */
i += 24;
len -= 24;
}
/*------------------------------------- handle the last 23 bytes */
c += k.length;
if(len > 0) {
if(len >= 8) {
a += gatherLongLE(k, i);
if(len >= 16) {
b += gatherLongLE(k, i + 8);
// this is bit asymmetric; LSB is reserved for length (see
// above)
if(len > 16) {
c += (gatherPartialLongLE(k, i + 16, len - 16) << 8);
}
} else if(len > 8) {
b += gatherPartialLongLE(k, i + 8, len - 8);
}
} else {
a += gatherPartialLongLE(k, i, len);
}
}
/* mix64(a, b, c); */
a -= b;
a -= c;
a ^= (c >> 43);
b -= c;
b -= a;
b ^= (a << 9);
c -= a;
c -= b;
c ^= (b >> 8);
a -= b;
a -= c;
a ^= (c >> 38);
b -= c;
b -= a;
b ^= (a << 23);
c -= a;
c -= b;
c ^= (b >> 5);
a -= b;
a -= c;
a ^= (c >> 35);
b -= c;
b -= a;
b ^= (a << 49);
c -= a;
c -= b;
c ^= (b >> 11);
a -= b;
a -= c;
a ^= (c >> 12);
b -= c;
b -= a;
b ^= (a << 18);
c -= a;
c -= b;
c ^= (b >> 22);
/* mix64(a, b, c); */
return c;
}
/** perform unsigned extension of int to long */
private static final long uintToLong(final int i) {
long l = (long) i;
return (l << 32) >>> 32;
}
/** gather a long from the specified index into the byte array */
private static final long gatherLongLE(final byte[] data, final int index) {
int i1 = gatherIntLE(data, index);
long l2 = gatherIntLE(data, index + 4);
return uintToLong(i1) | (l2 << 32);
}
/**
* gather a partial long from the specified index using the specified number
* of bytes into the byte array
*/
private static final long gatherPartialLongLE(final byte[] data, final int index, final int available) {
if(available >= 4) {
int i = gatherIntLE(data, index);
long l = uintToLong(i);
int left = available - 4;
if(left == 0) {
return l;
}
int i2 = gatherPartialIntLE(data, index + 4, left);
l <<= (left << 3);
l |= (long) i2;
return l;
} else {
return (long) gatherPartialIntLE(data, index, available);
}
}
/** gather an int from the specified index into the byte array */
private static final int gatherIntLE(final byte[] data, final int index) {
int i = data[index] & 0xFF;
i |= (data[index + 1] & 0xFF) << 8;
i |= (data[index + 2] & 0xFF) << 16;
i |= (data[index + 3] << 24);
return i;
}
/**
* gather a partial int from the specified index using the specified number
* of bytes into the byte array
*/
private static final int gatherPartialIntLE(final byte[] data, final int index, final int available) {
int i = data[index] & 0xFF;
if(available > 1) {
i |= (data[index + 1] & 0xFF) << 8;
if(available > 2) {
i |= (data[index + 2] & 0xFF) << 16;
}
}
return i;
}
}
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