From: Yann Duplouy <yann.duplouy@inria.fr>
Date: Tue, 12 Nov 2019 10:29:59 +0000 (+0100)
Subject: Fixes to xbt::random
X-Git-Tag: v3.25~386^2~4
X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/commitdiff_plain/61dd4dd6b2ecde25d99a11093aa01ed7ded944b9

Fixes to xbt::random
---

diff --git a/include/xbt/random.hpp b/include/xbt/random.hpp
index cf2b168c18..3ca1db16e5 100644
--- a/include/xbt/random.hpp
+++ b/include/xbt/random.hpp
@@ -15,6 +15,7 @@ int uniform_int(int, int);
 double uniform_real(double, double);
 double exponential(double);
 double normal(double, double);
+void set_mersenne_seed(int);
 } // namespace random
 } // namespace xbt
 } // namespace simgrid
diff --git a/src/xbt/random.cpp b/src/xbt/random.cpp
index 03c544a053..46f2a0fcb6 100644
--- a/src/xbt/random.cpp
+++ b/src/xbt/random.cpp
@@ -42,25 +42,25 @@ double uniform_real(double min, double 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 -1 / lambda * log(uniform_real(0, 1));
 }
 
 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;
+  double u1 = 0;
   while (u1 < std::numeric_limits<double>::min()) {
-    numeratorA = mt19937_gen() - mt19937_gen.min();
-    u1         = numeratorA / divisor;
+    u1 = uniform_real(0, 1);
   }
-  double z0 = sqrt(-2.0 * log(numeratorA / divisor)) * cos(2 * M_PI * numeratorB / divisor);
+  double u2 = uniform_real(0, 1);
+  double z0 = sqrt(-2.0 * log(u1)) * cos(2 * M_PI * u2);
   return z0 * sd + mean;
 }
 
+void set_mersenne_seed(int seed)
+{
+  mt19937_gen.seed(seed);
+}
+
 } // namespace random
 } // namespace xbt
 } // namespace simgrid