Cast integer inputs to double like STL

Author: mborland

include/boost/math/special_functions/log1p.hpp

@@ -430,6 +430,21 @@ inline typename tools::promote_args<T>::type log1p(T x)
 {
    return boost::math::log1p(x, policies::policy<>());
 }
+
+// Standard library casts integer inputs of special functions to double so follow precedence
+// See: https://en.cppreference.com/w/cpp/numeric/math/log1p
+template <BOOST_MATH_ARBITRARY_INTEGER T>
+inline tools::promote_args_t<T> log1p(T x)
+{
+   return boost::math::log1p(static_cast<double>(x), policies::policy<>());
+}
+
+template <BOOST_MATH_ARBITRARY_INTEGER T, BOOST_MATH_POLICY Policy>
+inline tools::promote_args_t<T> log1p(T x, const Policy& pol)
+{
+   return boost::math::log1p(static_cast<double>(x), pol);
+}
+
 //
 // Compute log(1+x)-x:
 //