org.cloudgraph.common.hash.Jenkins32 Maven / Gradle / Ivy
package org.cloudgraph.common.hash;
import static java.lang.Integer.rotateLeft;
import java.io.FileInputStream;
import java.io.IOException;
/**
* 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.
*
*
* @see lookup3.c
* @see Hash Functions (and how this
* function compares to others such as CRC, MD?, etc
* @see Has update on the
* Dr. Dobbs Article
*/
public class Jenkins32 implements Hash32 {
private static final int BYTE_MASK = 0xff;
private static volatile Jenkins32 INSTANCE;
public static Jenkins32 instance() {
if (INSTANCE == null)
initInstance();
return INSTANCE;
}
private static synchronized void initInstance() {
if (INSTANCE == null)
INSTANCE = new Jenkins32();
}
@Override
public int hash(byte[] bytes) {
return hash(bytes, 0, bytes.length, -1);
}
@Override
public int hash(byte[] bytes, int initval) {
return hash(bytes, 0, bytes.length, initval);
}
@Override
public int hash(byte[] data, int offset, int length) {
return hash(data, 0, length, -1);
}
/**
* 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.
*
*
* 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. [email protected]. 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 int hash(byte[] key, int off, int nbytes, int initval) {
int length = nbytes;
int a, b, c;
a = b = c = 0xdeadbeef + length + initval;
int offset = off;
for (; length > 12; offset += 12, length -= 12) {
a += (key[offset] & BYTE_MASK);
a += ((key[offset + 1] & BYTE_MASK) << 8);
a += ((key[offset + 2] & BYTE_MASK) << 16);
a += ((key[offset + 3] & BYTE_MASK) << 24);
b += (key[offset + 4] & BYTE_MASK);
b += ((key[offset + 5] & BYTE_MASK) << 8);
b += ((key[offset + 6] & BYTE_MASK) << 16);
b += ((key[offset + 7] & BYTE_MASK) << 24);
c += (key[offset + 8] & BYTE_MASK);
c += ((key[offset + 9] & BYTE_MASK) << 8);
c += ((key[offset + 10] & BYTE_MASK) << 16);
c += ((key[offset + 11] & BYTE_MASK) << 24);
/*
* 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 -= c;
a ^= rotateLeft(c, 4);
c += b;
b -= a;
b ^= rotateLeft(a, 6);
a += c;
c -= b;
c ^= rotateLeft(b, 8);
b += a;
a -= c;
a ^= rotateLeft(c, 16);
c += b;
b -= a;
b ^= rotateLeft(a, 19);
a += c;
c -= b;
c ^= rotateLeft(b, 4);
b += a;
}
// -------------------------------- last block: affect all 32 bits of
// (c)
switch (length) { // all the case statements fall through
case 12:
c += ((key[offset + 11] & BYTE_MASK) << 24);
case 11:
c += ((key[offset + 10] & BYTE_MASK) << 16);
case 10:
c += ((key[offset + 9] & BYTE_MASK) << 8);
case 9:
c += (key[offset + 8] & BYTE_MASK);
case 8:
b += ((key[offset + 7] & BYTE_MASK) << 24);
case 7:
b += ((key[offset + 6] & BYTE_MASK) << 16);
case 6:
b += ((key[offset + 5] & BYTE_MASK) << 8);
case 5:
b += (key[offset + 4] & BYTE_MASK);
case 4:
a += ((key[offset + 3] & BYTE_MASK) << 24);
case 3:
a += ((key[offset + 2] & BYTE_MASK) << 16);
case 2:
a += ((key[offset + 1] & BYTE_MASK) << 8);
case 1:
// noinspection PointlessArithmeticExpression
a += (key[offset + 0] & BYTE_MASK);
break;
case 0:
return c;
}
/*
* 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 -= rotateLeft(b, 14);
a ^= c;
a -= rotateLeft(c, 11);
b ^= a;
b -= rotateLeft(a, 25);
c ^= b;
c -= rotateLeft(b, 16);
a ^= c;
a -= rotateLeft(c, 4);
b ^= a;
b -= rotateLeft(a, 14);
c ^= b;
c -= rotateLeft(b, 24);
return c;
}
/**
* Compute the hash of the specified file
*
* @param args
* name of file to compute hash of.
* @throws IOException
* e
*/
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;
Jenkins32 hash = new Jenkins32();
try {
for (int length = in.read(bytes); length > 0; length = in.read(bytes)) {
value = hash.hash(bytes, 0, length, value);
}
} finally {
in.close();
}
System.out.println(Math.abs(value));
}
}