From 834682e65081b4aa51316767674ef62fa7711c55 Mon Sep 17 00:00:00 2001
From: Vinnie Falco <vinnie.falco@gmail.com>
Date: Mon, 17 Jul 2017 05:44:04 -0700
Subject: [PATCH] Add detail::sum_exceeds

---
 include/beast/core/detail/clamp.hpp | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/beast/core/detail/clamp.hpp b/include/beast/core/detail/clamp.hpp
index 21afeaaa..6d3a9ed5 100644
--- a/include/beast/core/detail/clamp.hpp
+++ b/include/beast/core/detail/clamp.hpp
@@ -8,8 +8,9 @@
 #ifndef BEAST_CORE_DETAIL_CLAMP_HPP
 #define BEAST_CORE_DETAIL_CLAMP_HPP
 
-#include <limits>
 #include <cstdlib>
+#include <limits>
+#include <type_traits>
 
 namespace beast {
 namespace detail {
@@ -34,6 +35,20 @@ clamp(UInt x, std::size_t limit)
     return static_cast<std::size_t>(x);
 }
 
+// return `true` if x + y > z, which are unsigned
+template<
+    class U1, class U2, class U3>
+constexpr
+bool
+sum_exceeds(U1 x, U2 y, U3 z)
+{
+    static_assert(
+        std::is_unsigned<U1>::value &&
+        std::is_unsigned<U2>::value &&
+        std::is_unsigned<U3>::value, "");
+    return y > z || x > z - y;
+}
+
 } // detail
 } // beast