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/*
* de.unkrig.commons - A general-purpose Java class library
*
* Copyright (c) 2012, Arno Unkrig
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
* following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the
* following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the
* following disclaimer in the documentation and/or other materials provided with the distribution.
* 3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote
* products derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package de.unkrig.commons.math;
import java.util.Arrays;
import de.unkrig.commons.lang.protocol.Producer;
/**
* A collection of utility methods related to mathematical sequences.
*/
public final
class Sequences {
private Sequences() {}
/**
* Produces a periodic sequence of random, but unique {@link Long}s with values ranging from 0 to {@code period -
* 1}.
*/
public static Producer
randomSequence(long period) {
return randomSequence(System.nanoTime(), period);
}
/**
* Produces a periodic sequence of random, but unique {@link Long}s with values ranging from 0 to {@code period -
* 1}. For identical seeds, the returned sequences will be identical.
*/
public static Producer
randomSequence(final long seed, final long period) {
if (period < 0L) throw new IllegalArgumentException();
int idx = Arrays.binarySearch(M, period + 1);
if (idx < 0) idx = -idx - 1;
if (idx == M.length) idx--; // Period is in the range 2^63 - 25 ... 2^63 - 1
final long m = M[idx];
long a = A[idx];
final Producer lcg = multiplicativeCongruentialGenerator(seed, m, a);
return new Producer() {
@Override public Long
produce() {
for (;;) {
@SuppressWarnings("null") long result = lcg.produce() - 1;
if (result < period) return result;
}
}
};
}
private static final long[] M = {
(1L << 3) - 1L,
(1L << 4) - 3L, (1L << 5) - 1L, (1L << 6) - 3L, (1L << 7) - 1L,
(1L << 8) - 5L, (1L << 9) - 3L, (1L << 10) - 3L, (1L << 11) - 9L,
(1L << 12) - 3L, (1L << 13) - 1L, (1L << 14) - 3L, (1L << 15) - 19L,
(1L << 16) - 15L, (1L << 17) - 1L, (1L << 18) - 5L, (1L << 19) - 1L,
(1L << 20) - 3L, (1L << 21) - 9L, (1L << 22) - 3L, (1L << 23) - 15L,
(1L << 24) - 3L, (1L << 25) - 39L, (1L << 26) - 5L, (1L << 27) - 39L,
(1L << 28) - 57L, (1L << 29) - 3L, (1L << 30) - 35L, (1L << 31) - 1L,
(1L << 32) - 5L, (1L << 33) - 9L, (1L << 34) - 41L, (1L << 35) - 31L,
(1L << 36) - 5L, (1L << 37) - 25L, (1L << 38) - 45L, (1L << 39) - 7L,
(1L << 40) - 87L, (1L << 41) - 21L, (1L << 42) - 11L, (1L << 43) - 57L,
(1L << 44) - 17L, (1L << 45) - 55L, (1L << 46) - 21L, (1L << 47) - 115L,
(1L << 48) - 59L, (1L << 48) - 59L, (1L << 50) - 27L, (1L << 51) - 129L,
(1L << 52) - 47L, (1L << 53) - 111L, (1L << 54) - 33L, (1L << 55) - 55L,
(1L << 56) - 5L, (1L << 57) - 13L, (1L << 58) - 27L, (1L << 59) - 55L,
(1L << 60) - 93L, (1L << 61) - 1L, (1L << 62) - 57L, (1L << 63) - 25L,
Long.MAX_VALUE,
};
private static final long[] A = {
5L,
7L, 11L, 31L, 23L,
33L, 35L, 65L, 995L,
209L, 884L, 572L, 219L,
17364L, 43165L, 92717L, 283741L,
380985L, 360889L, 914334L, 653276L,
6423135L, 25907312L, 26590841L, 45576512L,
246049789L, 520332806L, 771645345L, 1583458089L,
1588635695L, 7425194315L, 5295517759L, 3124199165L,
49865143810L, 76886758244L, 17838542566L, 61992693052L,
1038914804222L, 140245111714L, 2214813540776L, 4928052325348L,
6307617245999L, 25933916233908L, 63975993200055L, 72624924005429L,
49235258628958L, 265609885904224L, 1087141320185010L, 349044191547257L,
4359287924442956L, 2082839274626558L, 9131148267933071L, 33266544676670489L,
4595551687825993L, 75953708294752990L, 101565695086122187L, 346764851511064641L,
561860773102413563L, 1351750484049952003L, 2774243619903564593L, 4645906587823291368L,
};
/**
* Produces a periodic sequence of random, but unique {@link Long}s with values ranging from min to
* max{@code - 1}. The period of the sequence is {@code max - min}. For identical seeds, the
* returned sequences will be identical.
*/
public static Producer
randomSequence(long seed, final long min, long max) {
final Producer delegate = randomSequence(seed, max - min);
return new Producer() {
@SuppressWarnings("null") @Override public Long
produce() {
return delegate.produce() + min;
}
};
}
/**
* See Wikipedia article: Linear congruential
* generator.
*/
public static Producer
linearCongruentialGenerator(final long seed, final long m, final long a, final long c) {
return new Producer() {
long x = seed;
@Override public Long
produce() {
this.x = (a * this.x + c) % m;
return this.x;
}
};
}
/**
* See Wikipedia article: Linear congruential
* generator.
*
* Notice that this variant of a congruential generator produces values starting at one, not starting at
* zero!
*/
public static Producer
multiplicativeCongruentialGenerator(final long seed, final long m, final long a) {
return new Producer() {
long x = 1 + ((0x7fffffffffffffffL & seed) % (m - 1));
@Override public Long
produce() {
this.x = (a * this.x) % m;
return this.x;
}
};
}
}
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