Fix PR#20843: binomial_distribution<unsigned> is broken. Add test to ensure that signed and unsigned verstions produce the same sequence.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@217976 91177308-0d34-0410-b5e6-96231b3b80d8

test/numerics/rand/rand.dis/rand.dist.bern/rand.dist.bern.bin/eval.pass.cpp

@@ -321,6 +321,17 @@ int main()
         assert(std::abs(skew - x_skew) < 0.01);
         assert(std::abs((kurtosis - x_kurtosis) / x_kurtosis) < 0.01);
     }
+    {
+        const int N = 100000;
+        std::mt19937 gen1;
+        std::mt19937 gen2;
+
+        std::binomial_distribution<>         dist1(5, 0.1);
+        std::binomial_distribution<unsigned> dist2(5, 0.1);
+
+        for(int i = 0; i < N; ++i)
+            assert(dist1(gen1) == dist2(gen2));
+    }
     {
         typedef std::binomial_distribution<> D;
         typedef std::mt19937 G;