[gcc r14-9551] libstdc++: Fix infinite loop in std::binomial_distribution [PR114359]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:07e03761a7fc1626a6a74ed957e117f56981558c

commit r14-9551-g07e03761a7fc1626a6a74ed957e117f56981558c
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Mar 18 13:22:17 2024 +0000

    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.

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

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
+}