diff --git a/src/java/org/apache/cassandra/utils/PrimeFinder.java b/src/java/org/apache/cassandra/utils/PrimeFinder.java deleted file mode 100644 index 4df63d9ab7..0000000000 --- a/src/java/org/apache/cassandra/utils/PrimeFinder.java +++ /dev/null @@ -1,162 +0,0 @@ -/* -* 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.util.Arrays; - -/** - * Used to keep hash table capacities prime numbers. Not of interest for users; - * only for implementors of hashtables. - * - *

- * Choosing prime numbers as hash table capacities is a good idea to keep them - * working fast, particularly under hash table expansions. - * - */ -public final class PrimeFinder -{ - /** - * The largest prime this class can generate; currently equal to - * Integer.MAX_VALUE. - */ - public static final int largestPrime = Integer.MAX_VALUE; // yes, it is - // prime. - - /** - * The prime number list consists of 11 chunks. - * - * Each chunk contains prime numbers. - * - * A chunk starts with a prime P1. The next element is a prime P2. P2 is the - * smallest prime for which holds: P2 >= 2*P1. - * - * The next element is P3, for which the same holds with respect to P2, and - * so on. - * - * Chunks are chosen such that for any desired capacity >= 1000 the list - * includes a prime number <= desired capacity * 1.11. - * - * Therefore, primes can be retrieved which are quite close to any desired - * capacity, which in turn avoids wasting memory. - * - * For example, the list includes - * 1039,1117,1201,1277,1361,1439,1523,1597,1759,1907,2081. - * - * So if you need a prime >= 1040, you will find a prime <= 1040*1.11=1154. - * - * Chunks are chosen such that they are optimized for a hashtable - * growthfactor of 2.0; - * - * If your hashtable has such a growthfactor then, after initially "rounding - * to a prime" upon hashtable construction, it will later expand to prime - * capacities such that there exist no better primes. - * - * In total these are about 32*10=320 numbers -> 1 KB of static memory - * needed. - * - * If you are stingy, then delete every second or fourth chunk. - */ - - private static final int[] primeCapacities = { - // chunk #0 - largestPrime, - - // chunk #1 - 5, 11, 23, 47, 97, 197, 397, 797, 1597, 3203, 6421, 12853, 25717, - 51437, 102877, 205759, 411527, 823117, 1646237, 3292489, 6584983, - 13169977, 26339969, 52679969, 105359939, 210719881, 421439783, - 842879579, 1685759167, - - // chunk #2 - 433, 877, 1759, 3527, 7057, 14143, 28289, 56591, 113189, 226379, - 452759, 905551, 1811107, 3622219, 7244441, 14488931, 28977863, - 57955739, 115911563, 231823147, 463646329, 927292699, 1854585413, - - // chunk #3 - 953, 1907, 3821, 7643, 15287, 30577, 61169, 122347, 244703, 489407, - 978821, 1957651, 3915341, 7830701, 15661423, 31322867, 62645741, - 125291483, 250582987, 501165979, 1002331963, 2004663929, - - // chunk #4 - 1039, 2081, 4177, 8363, 16729, 33461, 66923, 133853, 267713, - 535481, 1070981, 2141977, 4283963, 8567929, 17135863, 34271747, - 68543509, 137087021, 274174111, 548348231, 1096696463, - - // chunk #5 - 31, 67, 137, 277, 557, 1117, 2237, 4481, 8963, 17929, 35863, 71741, - 143483, 286973, 573953, 1147921, 2295859, 4591721, 9183457, - 18366923, 36733847, 73467739, 146935499, 293871013, 587742049, - 1175484103, - - // chunk #6 - 599, 1201, 2411, 4831, 9677, 19373, 38747, 77509, 155027, 310081, - 620171, 1240361, 2480729, 4961459, 9922933, 19845871, 39691759, - 79383533, 158767069, 317534141, 635068283, 1270136683, - - // chunk #7 - 311, 631, 1277, 2557, 5119, 10243, 20507, 41017, 82037, 164089, - 328213, 656429, 1312867, 2625761, 5251529, 10503061, 21006137, - 42012281, 84024581, 168049163, 336098327, 672196673, 1344393353, - - // chunk #8 - 3, 7, 17, 37, 79, 163, 331, 673, 1361, 2729, 5471, 10949, 21911, - 43853, 87719, 175447, 350899, 701819, 1403641, 2807303, 5614657, - 11229331, 22458671, 44917381, 89834777, 179669557, 359339171, - 718678369, 1437356741, - - // chunk #9 - 43, 89, 179, 359, 719, 1439, 2879, 5779, 11579, 23159, 46327, - 92657, 185323, 370661, 741337, 1482707, 2965421, 5930887, 11861791, - 23723597, 47447201, 94894427, 189788857, 379577741, 759155483, - 1518310967, - - // chunk #10 - 379, 761, 1523, 3049, 6101, 12203, 24407, 48817, 97649, 195311, - 390647, 781301, 1562611, 3125257, 6250537, 12501169, 25002389, - 50004791, 100009607, 200019221, 400038451, 800076929, 1600153859 }; - - static - { // initializer - // The above prime numbers are formatted for human readability. - // To find numbers fast, we sort them once and for all. - - Arrays.sort(primeCapacities); - } - - /** - * Returns a prime number which is >= desiredCapacity and - * very close to desiredCapacity (within 11% if - * desiredCapacity >= 1000). - * - * @param desiredCapacity - * the capacity desired by the user. - * @return the capacity which should be used for a hashtable. - */ - public static final int nextPrime(int desiredCapacity) - { - int i = Arrays.binarySearch(primeCapacities, desiredCapacity); - if (i < 0) - { - // desired capacity not found, choose next prime greater - // than desired capacity - i = -i - 1; // remember the semantics of binarySearch... - } - return primeCapacities[i]; - } -}