/**
* @(#) JenkinsHash.java 2011-08-18
*/
package org.streaminer.util.hash;
/**
* This is an implementation of Bob Jenkins' hash. It can produce both 32-bit
* and 64-bit hash values.
* <p>
* Generates same hash values as the <a
* href="http://www.burtleburtle.net/bob/hash/doobs.html">original
* implementation written by Bob Jenkins</a>.
*
* @version $Revision: $
* @author $Author: vijaykandy $
*/
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;
}
public int hash(Object o) {
if (o == null) {
return 0;
}
if (o instanceof String) {
return hash32(((String) o).getBytes());
}
if (o instanceof byte[]) {
return hash32((byte[]) o);
}
return hash32(o.toString().getBytes());
}
public long hash64(Object o) {
if (o == null) {
return 0;
}
if (o instanceof String) {
return hash64(((String) o).getBytes());
}
if (o instanceof byte[]) {
return hash64((byte[]) o);
}
return hash64(o.toString().getBytes());
}
/**
* Returns a 64-bit hash value.
*
* @param input
* @return 64-bit hash value
*/
public long hash64(byte[] input) {
int pc = 0;
int pb = 0;
return hash(input, input.length, pc, pb, false);
}
/**
* Returns a 32-bit hash value.
*
* @param input
* @return 32-bit hash value
*/
public int hash32(byte[] input) {
int pc = 0;
int pb = 0;
return (int) hash(input, input.length, pc, pb, true);
}
/**
* Hash algorithm.
*
* @param k
* message on which hash is computed
* @param length
* message size
* @param pc
* primary init value
* @param pb
* secondary init value
* @param is32BitHash
* true if just 32-bit hash is expected.
* @return
*/
private long hash(byte[] k, int length, int pc, int pb, boolean is32BitHash) {
int a, b, c;
a = b = c = 0xdeadbeef + length + pc;
c += pb;
int offset = 0;
while (length > 12) {
a += k[offset + 0];
a += k[offset + 1] << 8;
a += k[offset + 2] << 16;
a += k[offset + 3] << 24;
b += k[offset + 4];
b += k[offset + 5] << 8;
b += k[offset + 6] << 16;
b += k[offset + 7] << 24;
c += k[offset + 8];
c += k[offset + 9] << 8;
c += k[offset + 10] << 16;
c += k[offset + 11] << 24;
// 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;
length -= 12;
offset += 12;
}
switch (length) {
case 12:
c += k[offset + 11] << 24;
case 11:
c += k[offset + 10] << 16;
case 10:
c += k[offset + 9] << 8;
case 9:
c += k[offset + 8];
case 8:
b += k[offset + 7] << 24;
case 7:
b += k[offset + 6] << 16;
case 6:
b += k[offset + 5] << 8;
case 5:
b += k[offset + 4];
case 4:
a += k[offset + 3] << 24;
case 3:
a += k[offset + 2] << 16;
case 2:
a += k[offset + 1] << 8;
case 1:
a += k[offset + 0];
break;
case 0:
return is32BitHash ? c : (c | ((long) (b << 32)));
}
// Final mixing of thrree 32-bit values in to 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);
return is32BitHash ? c : (c | ((long) (b << 32)));
}
private static long rot(int x, int distance) {
return (x << distance) | (x >> (32 - distance));
// return (x << distance) | (x >>> -distance);
}
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);
}
@Override
public long hash64(byte[] bytes, int length, int seed) {
return hash64(bytes);
}
}