Add cross-platform randomizer module.

The code uses two mechanisms for generating random numbers: srand()/rand(),
which is not thread-safe, and srandom()/random(), which is POSIX-specific.

Here I add a util/random.cc module that centralizes these calls, and unifies
some common usage patterns.  If the implementation is not good enough, we can
now change it in a single place.

To keep things simple, this uses the portable srand()/rand() but protects them
with a lock to avoid concurrency problems.

The hard part was to keep the regression tests passing: they rely on fixed
sequences of random numbers, so a small code change could break them very
thoroughly.  Util::rand(), for wide types like size_t, calls std::rand() not
once but twice.  This behaviour was generalized into utils::wide_rand() and
friends.

1 files changed, 2 insertions, 1 deletions

diff --git a/moses/Manager.cpp b/moses/Manager.cpp
index da0661aee..01ece66c0 100644
--- a/moses/Manager.cpp
+++ b/moses/Manager.cpp
@@ -54,6 +54,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 #endif
 
 #include "util/exception.hh"
+#include "util/random.hh"
 
 using namespace std;
 
@@ -418,7 +419,7 @@ void Manager::CalcLatticeSamples(size_t count, TrellisPathList &ret) const
       //cerr << endl;
 
       //draw the sample
-      float frandom = log((float)rand()/RAND_MAX);
+      const float frandom = log(util::rand_incl(0.0f, 1.0f));
       size_t position = 1;
       float sum = candidateScores[0];
       for (; position < candidateScores.size() && sum < frandom; ++position) {