mirror of https://gitee.com/bigwinds/arangodb
105 lines
4.3 KiB
C++
105 lines
4.3 KiB
C++
// This is the ``Mersenne Twister'' random number generator MT19937, which
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// generates pseudorandom integers uniformly distributed in 0..(2^32 - 1)
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// starting from any odd seed in 0..(2^32 - 1). This version is a recode
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// by Shawn Cokus (Cokus@math.washington.edu) on March 8, 1998 of a version by
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// Takuji Nishimura (who had suggestions from Topher Cooper and Marc Rieffel in
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// July-August 1997).
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//
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// Effectiveness of the recoding (on Goedel2.math.washington.edu, a DEC Alpha
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// running OSF/1) using GCC -O3 as a compiler: before recoding: 51.6 sec. to
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// generate 300 million random numbers; after recoding: 24.0 sec. for the same
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// (i.e., 46.5% of original time), so speed is now about 12.5 million random
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// number generations per second on this machine.
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//
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// According to the URL <http://www.math.keio.ac.jp/~matumoto/emt.html>
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// (and paraphrasing a bit in places), the Mersenne Twister is ``designed
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// with consideration of the flaws of various existing generators,'' has
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// a period of 2^19937 - 1, gives a sequence that is 623-dimensionally
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// equidistributed, and ``has passed many stringent tests, including the
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// die-hard test of G. Marsaglia and the load test of P. Hellekalek and
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// S. Wegenkittl.'' It is efficient in memory usage (typically using 2506
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// to 5012 bytes of static data, depending on data type sizes, and the code
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// is quite short as well). It generates random numbers in batches of 624
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// at a time, so the caching and pipelining of modern systems is exploited.
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// It is also divide- and mod-free.
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//
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// This library is free software; you can redistribute it and/or modify it
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// under the terms of the GNU Library General Public License as published by
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// the Free Software Foundation (either version 2 of the License or, at your
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// option, any later version). This library is distributed in the hope that
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// it will be useful, but WITHOUT ANY WARRANTY, without even the implied
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// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
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// the GNU Library General Public License for more details. You should have
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// received a copy of the GNU Library General Public License along with this
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// library; if not, write to the Free Software Foundation, Inc., 59 Temple
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// Place, Suite 330, Boston, MA 02111-1307, USA.
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//
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// The code as Shawn received it included the following notice:
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//
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// Copyright (C) 1997 Makoto Matsumoto and Takuji Nishimura. When
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// you use this, send an e-mail to <matumoto@math.keio.ac.jp> with
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// an appropriate reference to your work.
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//
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// It would be nice to CC: <Cokus@math.washington.edu> when you write.
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//
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// RandMT class created by Paul Gresham <gresham@mediavisual.com>
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// There seems to be a slight performance deficit in process creation
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// however I've not profiled the class to compare it with the straight
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// C code.
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//
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// Use of a class removes many C nasties and also allows you to easily
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// create multiple generators.
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// To compile on GNU a simple line is:
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// g++ -O3 RandMT.cc -o RandMT
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//
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#include <stdint.h>
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#include <cstdlib>
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// To keep this all as one file (easier distribution) the class is
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// in the code, cut'n'paste this bit to create a .h for use in
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// other programs
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#ifndef _RANDMT_H_
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#define _RANDMT_H_
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class RandMT {
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static const int N = 624; // length of state vector
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static const int M = 397; // a period parameter
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static const uint32_t K = 0x9908B0DFU; // a magic constant
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// If you want a single generator, consider using a singleton class
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// instead of trying to make these static.
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uint32_t state[N+1]; // state vector + 1 extra to not violate ANSI C
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uint32_t *next; // next random value is computed from here
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uint32_t initseed; //
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int left; // can *next++ this many times before reloading
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inline uint32_t hiBit(uint32_t u) {
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return u & 0x80000000U; // mask all but highest bit of u
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}
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inline uint32_t loBit(uint32_t u) {
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return u & 0x00000001U; // mask all but lowest bit of u
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}
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inline uint32_t loBits(uint32_t u) {
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return u & 0x7FFFFFFFU; // mask the highest bit of u
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}
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inline uint32_t mixBits(uint32_t u, uint32_t v) {
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return hiBit(u)|loBits(v); // move hi bit of u to hi bit of v
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}
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uint32_t reloadMT(void) ;
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public:
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RandMT() ;
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RandMT(uint32_t seed) ;
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uint32_t randomMT(void);
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void seedMT(uint32_t seed) ;
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};
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#endif // _RANDMT_H_
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