From: Yann Duplouy <yann.duplouy@inria.fr>
Date: Wed, 27 Nov 2019 15:07:43 +0000 (+0100)
Subject: Redraw if the random number is too close to max, to avoid modulo bias
X-Git-Tag: v3.26~1027^2~1
X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/commitdiff_plain/a5a63cee9b36d804e5442b421f1c3c3562b7a8ac

Redraw if the random number is too close to max, to avoid modulo bias

See framagit issue 43.
---

diff --git a/src/xbt/random.cpp b/src/xbt/random.cpp
index e7ba9e28b5..1886dbd54c 100644
--- a/src/xbt/random.cpp
+++ b/src/xbt/random.cpp
@@ -42,6 +42,9 @@ int uniform_int(int min, int max)
   xbt_assert(
       min <= max,
       "The maximum value for the uniform integer distribution must be greater than or equal to the minimum value");
+  while (value >= mt19937_gen.max() - mt19937_gen.max() % range) {
+    value = mt19937_gen();
+  }
   return value % range + min;
 }