Fix XbtRandom::uniform_int() when used with large range.

[simgrid.git] / src / xbt / random.cpp

diff --git a/src/xbt/random.cpp b/src/xbt/random.cpp
index dd4b3db..088545e 100644 (file)
--- a/src/xbt/random.cpp
+++ b/src/xbt/random.cpp
@@ -1,17 +1,44 @@
-/* Copyright (c) 2019-2020. The SimGrid Team. All rights reserved.               */
+/* Copyright (c) 2019-2021. 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 <fstream>
+#include <iostream>
 #include <limits>
 #include <memory>
+#include <string>
+#include <xbt/log.hpp>
+#include <xbt/random.hpp>
+
+XBT_LOG_EXTERNAL_CATEGORY(xbt);
+XBT_LOG_NEW_DEFAULT_SUBCATEGORY(xbt_random, xbt, "Random");
 
 namespace simgrid {
 namespace xbt {
 namespace random {
 
+bool Random::read_state(const std::string& filename)
+{
+  std::ifstream file(filename);
+  file >> mt19937_gen;
+  file.close();
+  if (file.fail())
+    XBT_WARN("Could not save the RNG state to file %s.", filename.c_str());
+  return not file.fail();
+}
+
+bool Random::write_state(const std::string& filename) const
+{
+  std::ofstream file(filename);
+  file << mt19937_gen;
+  file.close();
+  if (file.fail())
+    XBT_WARN("Could not read the RNG state from file %s.", filename.c_str());
+  return not file.fail();
+}
+
 int StdRandom::uniform_int(int min, int max)
 {
   std::uniform_int_distribution<> dist(min, max);
@@ -38,15 +65,21 @@ double StdRandom::normal(double mean, double sd)
 
 int XbtRandom::uniform_int(int min, int max)
 {
-  unsigned long range  = max - min + 1;
+  unsigned long range = static_cast<unsigned>(max) - static_cast<unsigned>(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.");
+  xbt_assert(range <= decltype(mt19937_gen)::max(),
+             "Overflow in the uniform integer distribution, please use a smaller range.");
+  if (range == decltype(mt19937_gen)::max())
+    return static_cast<int>(mt19937_gen() + min);
+
+  ++range;
+  unsigned long limit = decltype(mt19937_gen)::max() - decltype(mt19937_gen)::max() % range;
   unsigned long value;
   do {
     value = mt19937_gen();
-  } while (value >= decltype(mt19937_gen)::max() - decltype(mt19937_gen)::max() % range);
-  return value % range + min;
+  } while (value >= limit);
+  return static_cast<int>(value % range + min);
 }
 
 double XbtRandom::uniform_real(double min, double max)
@@ -57,7 +90,7 @@ double XbtRandom::uniform_real(double min, double max)
   do {
     numerator = mt19937_gen() - decltype(mt19937_gen)::min();
   } while (numerator == divisor);
-  return min + (max - min) * numerator / divisor;
+  return min + (max - min) * static_cast<double>(numerator) / divisor;
 }
 
 double XbtRandom::exponential(double lambda)
@@ -76,15 +109,15 @@ double XbtRandom::normal(double mean, double sd)
   return z0 * sd + mean;
 }
 
-static std::unique_ptr<Random> default_random(new XbtRandom);
+static std::unique_ptr<Random> default_random = std::make_unique<XbtRandom>();
 
 void set_implem_xbt()
 {
-  default_random.reset(new XbtRandom);
+  default_random = std::make_unique<XbtRandom>();
 }
 void set_implem_std()
 {
-  default_random.reset(new StdRandom);
+  default_random = std::make_unique<StdRandom>();
 }
 
 void set_mersenne_seed(int seed)
@@ -92,6 +125,16 @@ void set_mersenne_seed(int seed)
   default_random->set_seed(seed);
 }
 
+bool read_mersenne_state(const std::string& filename)
+{
+  return default_random->read_state(filename);
+}
+
+bool write_mersenne_state(const std::string& filename)
+{
+  return default_random->write_state(filename);
+}
+
 int uniform_int(int min, int max)
 {
   return default_random->uniform_int(min, max);