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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.

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/*
 * 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.cassandra.utils;

import java.nio.ByteBuffer;

/**
 * This is a very fast, non-cryptographic hash suitable for general hash-based
 * lookup. See http://murmurhash.googlepages.com/ for more details.
 *
 * hash32() and hash64() are MurmurHash 2.0.
 *
 * hash3_x64_128() is *almost* MurmurHash 3.0.  It was supposed to match, but we didn't catch a sign bug with
 * the result that it doesn't.  Unfortunately, we can't change it now without breaking Murmur3Partitioner. *
 * 
 * 

* The C version of MurmurHash 2.0 found at that site was ported to Java by * Andrzej Bialecki (ab at getopt org). *

*/ public class MurmurHash { public static int hash32(ByteBuffer data, int offset, int length, int seed) { int m = 0x5bd1e995; int r = 24; int h = seed ^ length; int len_4 = length >> 2; for (int i = 0; i < len_4; i++) { int i_4 = i << 2; int k = data.get(offset + i_4 + 3); k = k << 8; k = k | (data.get(offset + i_4 + 2) & 0xff); k = k << 8; k = k | (data.get(offset + i_4 + 1) & 0xff); k = k << 8; k = k | (data.get(offset + i_4 + 0) & 0xff); k *= m; k ^= k >>> r; k *= m; h *= m; h ^= k; } // avoid calculating modulo int len_m = len_4 << 2; int left = length - len_m; if (left != 0) { if (left >= 3) { h ^= (int) data.get(offset + length - 3) << 16; } if (left >= 2) { h ^= (int) data.get(offset + length - 2) << 8; } if (left >= 1) { h ^= (int) data.get(offset + length - 1); } h *= m; } h ^= h >>> 13; h *= m; h ^= h >>> 15; return h; } public static long hash2_64(ByteBuffer key, int offset, int length, long seed) { long m64 = 0xc6a4a7935bd1e995L; int r64 = 47; long h64 = (seed & 0xffffffffL) ^ (m64 * length); int lenLongs = length >> 3; for (int i = 0; i < lenLongs; ++i) { int i_8 = i << 3; long k64 = ((long) key.get(offset+i_8+0) & 0xff) + (((long) key.get(offset+i_8+1) & 0xff)<<8) + (((long) key.get(offset+i_8+2) & 0xff)<<16) + (((long) key.get(offset+i_8+3) & 0xff)<<24) + (((long) key.get(offset+i_8+4) & 0xff)<<32) + (((long) key.get(offset+i_8+5) & 0xff)<<40) + (((long) key.get(offset+i_8+6) & 0xff)<<48) + (((long) key.get(offset+i_8+7) & 0xff)<<56); k64 *= m64; k64 ^= k64 >>> r64; k64 *= m64; h64 ^= k64; h64 *= m64; } int rem = length & 0x7; switch (rem) { case 0: break; case 7: h64 ^= (long) key.get(offset + length - rem + 6) << 48; case 6: h64 ^= (long) key.get(offset + length - rem + 5) << 40; case 5: h64 ^= (long) key.get(offset + length - rem + 4) << 32; case 4: h64 ^= (long) key.get(offset + length - rem + 3) << 24; case 3: h64 ^= (long) key.get(offset + length - rem + 2) << 16; case 2: h64 ^= (long) key.get(offset + length - rem + 1) << 8; case 1: h64 ^= (long) key.get(offset + length - rem); h64 *= m64; } h64 ^= h64 >>> r64; h64 *= m64; h64 ^= h64 >>> r64; return h64; } protected static long getblock(ByteBuffer key, int offset, int index) { int i_8 = index << 3; int blockOffset = offset + i_8; return ((long) key.get(blockOffset + 0) & 0xff) + (((long) key.get(blockOffset + 1) & 0xff) << 8) + (((long) key.get(blockOffset + 2) & 0xff) << 16) + (((long) key.get(blockOffset + 3) & 0xff) << 24) + (((long) key.get(blockOffset + 4) & 0xff) << 32) + (((long) key.get(blockOffset + 5) & 0xff) << 40) + (((long) key.get(blockOffset + 6) & 0xff) << 48) + (((long) key.get(blockOffset + 7) & 0xff) << 56); } protected static long rotl64(long v, int n) { return ((v << n) | (v >>> (64 - n))); } protected static long fmix(long k) { k ^= k >>> 33; k *= 0xff51afd7ed558ccdL; k ^= k >>> 33; k *= 0xc4ceb9fe1a85ec53L; k ^= k >>> 33; return k; } public static void hash3_x64_128(ByteBuffer key, int offset, int length, long seed, long[] result) { final int nblocks = length >> 4; // Process as 128-bit blocks. long h1 = seed; long h2 = seed; long c1 = 0x87c37b91114253d5L; long c2 = 0x4cf5ad432745937fL; //---------- // body for(int i = 0; i < nblocks; i++) { long k1 = getblock(key, offset, i*2+0); long k2 = getblock(key, offset, i*2+1); k1 *= c1; k1 = rotl64(k1,31); k1 *= c2; h1 ^= k1; h1 = rotl64(h1,27); h1 += h2; h1 = h1*5+0x52dce729; k2 *= c2; k2 = rotl64(k2,33); k2 *= c1; h2 ^= k2; h2 = rotl64(h2,31); h2 += h1; h2 = h2*5+0x38495ab5; } //---------- // tail // Advance offset to the unprocessed tail of the data. offset += nblocks * 16; long k1 = 0; long k2 = 0; switch(length & 15) { case 15: k2 ^= ((long) key.get(offset+14)) << 48; case 14: k2 ^= ((long) key.get(offset+13)) << 40; case 13: k2 ^= ((long) key.get(offset+12)) << 32; case 12: k2 ^= ((long) key.get(offset+11)) << 24; case 11: k2 ^= ((long) key.get(offset+10)) << 16; case 10: k2 ^= ((long) key.get(offset+9)) << 8; case 9: k2 ^= ((long) key.get(offset+8)) << 0; k2 *= c2; k2 = rotl64(k2,33); k2 *= c1; h2 ^= k2; case 8: k1 ^= ((long) key.get(offset+7)) << 56; case 7: k1 ^= ((long) key.get(offset+6)) << 48; case 6: k1 ^= ((long) key.get(offset+5)) << 40; case 5: k1 ^= ((long) key.get(offset+4)) << 32; case 4: k1 ^= ((long) key.get(offset+3)) << 24; case 3: k1 ^= ((long) key.get(offset+2)) << 16; case 2: k1 ^= ((long) key.get(offset+1)) << 8; case 1: k1 ^= ((long) key.get(offset)); k1 *= c1; k1 = rotl64(k1,31); k1 *= c2; h1 ^= k1; }; //---------- // finalization h1 ^= length; h2 ^= length; h1 += h2; h2 += h1; h1 = fmix(h1); h2 = fmix(h2); h1 += h2; h2 += h1; result[0] = h1; result[1] = h2; } }




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