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diff --git a/boost/beast/core/detail/clamp.hpp b/boost/beast/core/detail/clamp.hpp
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+++ b/boost/beast/core/detail/clamp.hpp
@@ -0,0 +1,59 @@
+//
+// Copyright (c) 2016-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+#ifndef BOOST_BEAST_CORE_DETAIL_CLAMP_HPP
+#define BOOST_BEAST_CORE_DETAIL_CLAMP_HPP
+
+#include <cstdlib>
+#include <limits>
+#include <type_traits>
+
+namespace boost {
+namespace beast {
+namespace detail {
+
+template<class UInt>
+static
+std::size_t
+clamp(UInt x)
+{
+    if(x >= (std::numeric_limits<std::size_t>::max)())
+        return (std::numeric_limits<std::size_t>::max)();
+    return static_cast<std::size_t>(x);
+}
+
+template<class UInt>
+static
+std::size_t
+clamp(UInt x, std::size_t limit)
+{
+    if(x >= limit)
+        return 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
+} // boost
+
+#endif