Fix division by zero on 32bit systems.

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

diff --git a/src/xbt/random.cpp b/src/xbt/random.cpp
index 03c544a..04aa0fc 100644 (file)
--- a/src/xbt/random.cpp
+++ b/src/xbt/random.cpp
@@ -1,4 +1,4 @@
-/* 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. */
@@ -11,53 +11,81 @@
 namespace simgrid {
 namespace xbt {
 namespace random {
-std::mt19937 mt19937_gen;
+enum xbt_random_implem { XBT_RNG_xbt, XBT_RNG_std };
+static xbt_random_implem rng_implem = XBT_RNG_xbt;
+
+static std::mt19937 mt19937_gen;
+
+void set_implem_xbt()
+{
+  rng_implem = XBT_RNG_xbt;
+}
+void set_implem_std()
+{
+  rng_implem = XBT_RNG_std;
+}
+void set_mersenne_seed(int seed)
+{
+  mt19937_gen.seed(seed);
+}
 
 int uniform_int(int min, int max)
 {
-  unsigned long gmin   = mt19937_gen.min();
-  unsigned long gmax   = mt19937_gen.max();
-  unsigned long grange = gmax - gmin + 1;
+  if (rng_implem == XBT_RNG_std) {
+    std::uniform_int_distribution<> dist(min, max);
+    return dist(mt19937_gen);
+  }
+
   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;
-    }
+  unsigned long value  = mt19937_gen();
+  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.");
+  while (value >= decltype(mt19937_gen)::max() - decltype(mt19937_gen)::max() % range) {
+    value = mt19937_gen();
   }
+  return value % range + min;
 }
 
 double uniform_real(double min, double max)
 {
+  if (rng_implem == XBT_RNG_std) {
+    std::uniform_real_distribution<> dist(min, max);
+    return dist(mt19937_gen);
+  }
+
   // 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 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);
+  if (rng_implem == XBT_RNG_std) {
+    std::exponential_distribution<> dist(lambda);
+    return dist(mt19937_gen);
+  }
+
+  return -1.0 / lambda * log(uniform_real(0.0, 1.0));
 }
 
 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 u1                = numeratorA / divisor;
+  if (rng_implem == XBT_RNG_std) {
+    std::normal_distribution<> dist(mean, sd);
+    return dist(mt19937_gen);
+  }
+
+  double u1 = 0.0;
   while (u1 < std::numeric_limits<double>::min()) {
-    numeratorA = mt19937_gen() - mt19937_gen.min();
-    u1         = numeratorA / divisor;
+    u1 = uniform_real(0.0, 1.0);
   }
-  double z0 = sqrt(-2.0 * log(numeratorA / divisor)) * cos(2 * M_PI * numeratorB / divisor);
+  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;
 }