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

[Jonathan Wakely <jwakely@redhat.com>]

Tested x86_64-linux. Pushed to trunk.

Not a regression, but worth backporting.

-- >8 --

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.
---
 libstdc++-v3/include/bits/random.tcc                 |  2 +-
 .../random/binomial_distribution/114359.cc           | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 libstdc++-v3/testsuite/26_numerics/random/binomial_distribution/114359.cc

diff --git a/libstdc++-v3/include/bits/random.tcc b/libstdc++-v3/include/bits/random.tcc
index ade416390b3..8216883c448 100644
--- a/libstdc++-v3/include/bits/random.tcc
+++ b/libstdc++-v3/include/bits/random.tcc
@@ -1503,7 +1503,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  // sqrt(pi / 2)
 	  const double __spi_2 = 1.2533141373155002512078826424055226L;
 	  _M_s1 = std::sqrt(__np * __1p) * (1 + _M_d1 / (4 * __np));
-	  _M_s2 = std::sqrt(__np * __1p) * (1 + _M_d2 / (4 * _M_t * __1p));
+	  _M_s2 = std::sqrt(__np * __1p) * (1 + _M_d2 / (4 * (_M_t * __1p)));
 	  _M_c = 2 * _M_d1 / __np;
 	  _M_a1 = std::exp(_M_c) * _M_s1 * __spi_2;
 	  const double __a12 = _M_a1 + _M_s2 * __spi_2;
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 00000000000..c1e4c380bf9
--- /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
+}
-- 
2.44.0