X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/65e50c050d9856bf4728824596bf75d9b3b0ab6e..83e12528b0f7fde3d3fc54fe56626c2043c39280:/src/xbt/random.cpp

diff --git a/src/xbt/random.cpp b/src/xbt/random.cpp
index 7f8af6affb..dd4b3db6b4 100644
--- a/src/xbt/random.cpp
+++ b/src/xbt/random.cpp
@@ -1,58 +1,115 @@
-/* Copyright (c) 2019. The SimGrid Team. All rights reserved.               */
+/* Copyright (c) 2019-2020. The SimGrid Team. All rights reserved.               */
 
 /* This program is free software; you can redistribute it and/or modify it
  * under the terms of the license (GNU LGPL) which comes with this package. */
 
 #include "xbt/random.hpp"
 #include "xbt/asserts.h"
-#include <random>
+#include <limits>
+#include <memory>
 
 namespace simgrid {
 namespace xbt {
 namespace random {
-std::mt19937 mt19937_gen;
 
-int uniform_int(int min, int max)
+int StdRandom::uniform_int(int min, int max)
+{
+  std::uniform_int_distribution<> dist(min, max);
+  return dist(mt19937_gen);
+}
+
+double StdRandom::uniform_real(double min, double max)
+{
+  std::uniform_real_distribution<> dist(min, max);
+  return dist(mt19937_gen);
+}
+
+double StdRandom::exponential(double lambda)
+{
+  std::exponential_distribution<> dist(lambda);
+  return dist(mt19937_gen);
+}
+
+double StdRandom::normal(double mean, double sd)
+{
+  std::normal_distribution<> dist(mean, sd);
+  return dist(mt19937_gen);
+}
+
+int XbtRandom::uniform_int(int min, int max)
 {
-  unsigned long gmin   = mt19937_gen.min();
-  unsigned long gmax   = mt19937_gen.max();
-  unsigned long grange = gmax - gmin + 1;
   unsigned long range  = max - min + 1;
-  xbt_assert(range < grange || range == grange, "The current implementation of the uniform integer distribution does "
-                                                "not allow range to be higher than mt19937's range");
-  unsigned long mult       = grange / range;
-  unsigned long maxallowed = gmin + (mult + 1) * range - 1;
-  while (true) {
-    unsigned long value = mt19937_gen();
-    if (value > maxallowed) {
-    } else {
-      return value % range + min;
-    }
-  }
+  xbt_assert(min <= max,
+             "The minimum value for the uniform integer distribution must not be greater than the maximum value");
+  xbt_assert(range > 0, "Overflow in the uniform integer distribution, please use a smaller range.");
+  unsigned long value;
+  do {
+    value = mt19937_gen();
+  } while (value >= decltype(mt19937_gen)::max() - decltype(mt19937_gen)::max() % range);
+  return value % range + min;
 }
 
-double uniform_real(double min, double max)
+double XbtRandom::uniform_real(double min, double max)
 {
   // This reuses Boost's uniform real distribution ideas
-  unsigned long numerator = mt19937_gen() - mt19937_gen.min();
-  unsigned long divisor   = mt19937_gen.max() - mt19937_gen.min();
+  constexpr unsigned long divisor = decltype(mt19937_gen)::max() - decltype(mt19937_gen)::min();
+  unsigned long numerator;
+  do {
+    numerator = mt19937_gen() - decltype(mt19937_gen)::min();
+  } while (numerator == divisor);
   return min + (max - min) * numerator / divisor;
 }
 
+double XbtRandom::exponential(double lambda)
+{
+  return -1.0 / lambda * log(uniform_real(0.0, 1.0));
+}
+
+double XbtRandom::normal(double mean, double sd)
+{
+  double u1;
+  do {
+    u1 = uniform_real(0.0, 1.0);
+  } while (u1 < std::numeric_limits<double>::min());
+  double u2 = uniform_real(0.0, 1.0);
+  double z0 = sqrt(-2.0 * log(u1)) * cos(2.0 * M_PI * u2);
+  return z0 * sd + mean;
+}
+
+static std::unique_ptr<Random> default_random(new XbtRandom);
+
+void set_implem_xbt()
+{
+  default_random.reset(new XbtRandom);
+}
+void set_implem_std()
+{
+  default_random.reset(new StdRandom);
+}
+
+void set_mersenne_seed(int seed)
+{
+  default_random->set_seed(seed);
+}
+
+int uniform_int(int min, int max)
+{
+  return default_random->uniform_int(min, max);
+}
+
+double uniform_real(double min, double max)
+{
+  return default_random->uniform_real(min, max);
+}
+
 double exponential(double lambda)
 {
-  unsigned long numerator = mt19937_gen() - mt19937_gen.min();
-  unsigned long divisor   = mt19937_gen.max() - mt19937_gen.min();
-  return -1 / lambda * log(numerator / divisor);
+  return default_random->exponential(lambda);
 }
 
 double normal(double mean, double sd)
 {
-  unsigned long numeratorA = mt19937_gen() - mt19937_gen.min();
-  unsigned long numeratorB = mt19937_gen() - mt19937_gen.min();
-  unsigned long divisor    = mt19937_gen.max() - mt19937_gen.min();
-  double z0                = sqrt(-2.0 * log(numeratorA / divisor)) * cos(2 * M_PI * numeratorB / divisor);
-  return z0 * sd + mean;
+  return default_random->normal(mean, sd);
 }
 
 } // namespace random