From 9869e7a5152cc8e4e2a410c20820992d8bbcd405 Mon Sep 17 00:00:00 2001
From: Evan Miller <emmiller@gmail.com>
Date: Fri, 10 Jul 2020 07:08:07 -0400
Subject: [PATCH] Fix binomial_coefficient forwarding policy

This addresses an issue where unintended double-promotion could occur.

See #398.
---
 include/boost/math/special_functions/binomial.hpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/boost/math/special_functions/binomial.hpp b/include/boost/math/special_functions/binomial.hpp
index 9a24fc15b..2bbc1fb25 100644
--- a/include/boost/math/special_functions/binomial.hpp
+++ b/include/boost/math/special_functions/binomial.hpp
@@ -63,7 +63,13 @@ T binomial_coefficient(unsigned n, unsigned k, const Policy& pol)
 template <>
 inline float binomial_coefficient<float, policies::policy<> >(unsigned n, unsigned k, const policies::policy<>& pol)
 {
-   return policies::checked_narrowing_cast<float, policies::policy<> >(binomial_coefficient<double>(n, k, pol), "boost::math::binomial_coefficient<%1%>(unsigned,unsigned)");
+   typedef policies::normalise<
+       policies::policy<>,
+       policies::promote_float<true>,
+       policies::promote_double<false>,
+       policies::discrete_quantile<>,
+       policies::assert_undefined<> >::type forwarding_policy;
+   return policies::checked_narrowing_cast<float, forwarding_policy>(binomial_coefficient<double>(n, k, forwarding_policy()), "boost::math::binomial_coefficient<%1%>(unsigned,unsigned)");
 }
 
 template <class T>