libstdc++: Fix infinite loop in std::binomial_distribution [PR114359]

The multiplication (4 * _M_t * __1p) can wraparound to zero if _M_t is
unsigned and 4 * _M_t wraps to zero. The third operand has type double,
so do the second multiplication first, so that we aren't multiplying
integers.

libstdc++-v3/ChangeLog:

	PR libstdc++/114359
	* include/bits/random.tcc (binomial_distribution::param_type):
	Ensure arithmetic is done as type double.
	* testsuite/26_numerics/random/binomial_distribution/114359.cc: New test.

1 files changed, 12 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/26_numerics/random/binomial_distribution/114359.cc b/libstdc++-v3/testsuite/26_numerics/random/binomial_distribution/114359.cc
new file mode 100644
index 0000000..c1e4c38
--- /dev/null
+++ b/libstdc++-v3/testsuite/26_numerics/random/binomial_distribution/114359.cc
@@ -0,0 +1,12 @@
+// { dg-do run { target c++11 } }
+
+// Bug 114359 - std::binomial_distribution hangs in infinite loop
+
+#include <random>
+
+int main()
+{
+  std::default_random_engine g{};
+  std::binomial_distribution<std::uint32_t> b(1U << 30);
+  b(g);  // hangs forever
+}