comphelper/source/misc/random.cxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  *
   9  * Contributor(s):
  10  *   Copyright (C) 2012 Tino Kluge <tino.kluge@hrz.tu-chemnitz.de>
  11  */
  12
  13 #include <comphelper/random.hxx>
  14 #include <rtl/instance.hxx>
  15 #include <sal/log.hxx>
  16 #include <assert.h>
  17 #include <time.h>
  18 #include <random>
  19 #include <stdexcept>
  20
  21 // this is nothing but a simple wrapper around
  22 // the std::random generators
  23
  24 namespace comphelper
  25 {
  26 namespace rng
  27 {
  28
  29 // underlying random number generator
  30 // std::mt19937 implements the Mersenne twister algorithm which
  31 // is fast and has good statistical properties, it produces integers
  32 // in the range of [0, 2^32-1] internally
  33 // memory requirement: 625*sizeof(uint32_t)
  34 // http://en.wikipedia.org/wiki/Mersenne_twister
  35 #define STD_RNG_ALGO  std::mt19937
  36
  37 struct RandomNumberGenerator
  38 {
  39     STD_RNG_ALGO global_rng;
  40     RandomNumberGenerator()
  41     {
  42         try
  43         {
  44             std::random_device rd;
  45             // initialises the state of the global random number generator
  46             // should only be called once.
  47             // (note, a few std::variate_generator<> (like normal) have their
  48             // own state which would need a reset as well to guarantee identical
  49             // sequence of numbers, e.g. via myrand.distribution().reset())
  50             global_rng.seed(rd() ^ time(nullptr));
  51         }
  52         catch (std::runtime_error& e)
  53         {
  54             SAL_WARN("comphelper.random", "Using std::random_device failed: " << e.what());
  55             global_rng.seed(time(nullptr));
  56         }
  57     }
  58 };
  59
  60 class theRandomNumberGenerator : public rtl::Static<RandomNumberGenerator, theRandomNumberGenerator> {};
  61
  62 // re-initialises the state of the global random number generator
  63 void reseed(int i)
  64 {
  65     return theRandomNumberGenerator::get().global_rng.seed(i);
  66 }
  67
  68 // uniform ints [a,b] distribution
  69 int uniform_int_distribution(int a, int b)
  70 {
  71     std::uniform_int_distribution<int> dist(a, b);
  72     return dist(theRandomNumberGenerator::get().global_rng);
  73 }
  74
  75 // uniform ints [a,b] distribution
  76 unsigned int uniform_uint_distribution(unsigned int a, unsigned int b)
  77 {
  78     std::uniform_int_distribution<unsigned int> dist(a, b);
  79     return dist(theRandomNumberGenerator::get().global_rng);
  80 }
  81
  82 // uniform size_t [a,b] distribution
  83 size_t uniform_size_distribution(size_t a, size_t b)
  84 {
  85     std::uniform_int_distribution<size_t> dist(a, b);
  86     return dist(theRandomNumberGenerator::get().global_rng);
  87 }
  88
  89 // uniform size_t [a,b) distribution
  90 double uniform_real_distribution(double a, double b)
  91 {
  92     assert(a < b);
  93     std::uniform_real_distribution<double> dist(a, b);
  94     return dist(theRandomNumberGenerator::get().global_rng);
  95 }
  96
  97 } // namespace
  98 } // namespace
  99
 100 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */