From 72c9c492249c309812bf2b49fd3d2b335067f191 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Thu, 23 Mar 2017 19:22:42 +0200
Subject: [PATCH 1/2] Unroll cx_plus a bit.

---
 include/boost/mp11/detail/mp_count.hpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/boost/mp11/detail/mp_count.hpp b/include/boost/mp11/detail/mp_count.hpp
index c03128f..12bde18 100644
--- a/include/boost/mp11/detail/mp_count.hpp
+++ b/include/boost/mp11/detail/mp_count.hpp
@@ -36,6 +36,12 @@ template<class T1, class... T> constexpr std::size_t cx_plus(T1 t1, T... t)
     return t1 + cx_plus(t...);
 }
 
+template<class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class... T>
+constexpr std::size_t cx_plus(T1 t1, T2 t2, T3 t3, T4 t4, T5 t5, T6 t6, T7 t7, T8 t8, T9 t9, T10 t10, T... t)
+{
+    return t1 + t2 + t3 + t4 + t5 + t6 + t7 + t8 + t9 + t10 + cx_plus(t...);
+}
+
 template<template<class...> class L, class... T, class V> struct mp_count_impl<L<T...>, V>
 {
     using type = mp_size_t<cx_plus(std::is_same<T, V>::value...)>;

From 848c2ff82ca81046acc0a8343b7892a7738f0af1 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Thu, 23 Mar 2017 19:34:43 +0200
Subject: [PATCH 2/2] Add fold expr implementations of mp_count, mp_count_if

---
 include/boost/mp11/detail/mp_count.hpp | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/include/boost/mp11/detail/mp_count.hpp b/include/boost/mp11/detail/mp_count.hpp
index 12bde18..ef97827 100644
--- a/include/boost/mp11/detail/mp_count.hpp
+++ b/include/boost/mp11/detail/mp_count.hpp
@@ -24,7 +24,14 @@ namespace detail
 
 template<class L, class V> struct mp_count_impl;
 
-#if !defined( BOOST_MP11_NO_CONSTEXPR )
+#if defined( BOOST_MP11_HAS_FOLD_EXPRESSIONS )
+
+template<template<class...> class L, class... T, class V> struct mp_count_impl<L<T...>, V>
+{
+    using type = mp_size_t<(std::is_same<T, V>::value + ... + 0)>;
+};
+
+#elif !defined( BOOST_MP11_NO_CONSTEXPR )
 
 constexpr std::size_t cx_plus()
 {
@@ -66,7 +73,14 @@ namespace detail
 
 template<class L, template<class...> class P> struct mp_count_if_impl;
 
-#if !defined( BOOST_MP11_NO_CONSTEXPR )
+#if defined( BOOST_MP11_HAS_FOLD_EXPRESSIONS )
+
+template<template<class...> class L, class... T, template<class...> class P> struct mp_count_if_impl<L<T...>, P>
+{
+    using type = mp_size_t<(mp_to_bool<P<T>>::value + ... + 0)>;
+};
+
+#elif !defined( BOOST_MP11_NO_CONSTEXPR )
 
 template<template<class...> class L, class... T, template<class...> class P> struct mp_count_if_impl<L<T...>, P>
 {