Java tutorial
/* * @(#)$Id$ * * 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; } }