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diff --git a/boost/atomic/detail/integral_extend.hpp b/boost/atomic/detail/integral_extend.hpp
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+++ b/boost/atomic/detail/integral_extend.hpp
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+/*
+ * 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)
+ *
+ * Copyright (c) 2018 Andrey Semashev
+ */
+/*!
+ * \file   atomic/detail/integral_extend.hpp
+ *
+ * This header defines sign/zero extension utilities for Boost.Atomic. The tools assume two's complement signed integer representation.
+ */
+
+#ifndef BOOST_ATOMIC_DETAIL_INTEGRAL_EXTEND_HPP_INCLUDED_
+#define BOOST_ATOMIC_DETAIL_INTEGRAL_EXTEND_HPP_INCLUDED_
+
+#include <boost/atomic/detail/config.hpp>
+#include <boost/atomic/detail/bitwise_cast.hpp>
+#include <boost/atomic/detail/type_traits/integral_constant.hpp>
+#include <boost/atomic/detail/type_traits/is_signed.hpp>
+#include <boost/atomic/detail/type_traits/make_signed.hpp>
+#include <boost/atomic/detail/type_traits/make_unsigned.hpp>
+
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#pragma once
+#endif
+
+namespace boost {
+namespace atomics {
+namespace detail {
+
+template< typename Output, typename Input >
+BOOST_FORCEINLINE Output zero_extend_impl(Input input, atomics::detail::true_type) BOOST_NOEXCEPT
+{
+    // Note: If we are casting with truncation or to the same-sized output, don't cause signed integer overflow by this chain of conversions
+    return atomics::detail::bitwise_cast< Output >(static_cast< typename atomics::detail::make_unsigned< Output >::type >(
+        static_cast< typename atomics::detail::make_unsigned< Input >::type >(input)));
+}
+
+template< typename Output, typename Input >
+BOOST_FORCEINLINE Output zero_extend_impl(Input input, atomics::detail::false_type) BOOST_NOEXCEPT
+{
+    return static_cast< Output >(static_cast< typename atomics::detail::make_unsigned< Input >::type >(input));
+}
+
+//! Zero-extends or truncates (wraps) input operand to fit in the output type
+template< typename Output, typename Input >
+BOOST_FORCEINLINE Output zero_extend(Input input) BOOST_NOEXCEPT
+{
+    return atomics::detail::zero_extend_impl< Output >(input, atomics::detail::integral_constant< bool, atomics::detail::is_signed< Output >::value >());
+}
+
+//! Truncates (wraps) input operand to fit in the output type
+template< typename Output, typename Input >
+BOOST_FORCEINLINE Output integral_truncate(Input input) BOOST_NOEXCEPT
+{
+    // zero_extend does the truncation
+    return atomics::detail::zero_extend< Output >(input);
+}
+
+template< typename Output, typename Input >
+BOOST_FORCEINLINE Output sign_extend_impl(Input input, atomics::detail::true_type) BOOST_NOEXCEPT
+{
+    return atomics::detail::integral_truncate< Output >(input);
+}
+
+template< typename Output, typename Input >
+BOOST_FORCEINLINE Output sign_extend_impl(Input input, atomics::detail::false_type) BOOST_NOEXCEPT
+{
+    return static_cast< Output >(atomics::detail::bitwise_cast< typename atomics::detail::make_signed< Input >::type >(input));
+}
+
+//! Sign-extends or truncates (wraps) input operand to fit in the output type
+template< typename Output, typename Input >
+BOOST_FORCEINLINE Output sign_extend(Input input) BOOST_NOEXCEPT
+{
+    return atomics::detail::sign_extend_impl< Output >(input, atomics::detail::integral_constant< bool, sizeof(Output) <= sizeof(Input) >());
+}
+
+//! Sign-extends or truncates (wraps) input operand to fit in the output type
+template< typename Output, typename Input >
+BOOST_FORCEINLINE Output integral_extend(Input input, atomics::detail::true_type) BOOST_NOEXCEPT
+{
+    return atomics::detail::sign_extend< Output >(input);
+}
+
+//! Zero-extends or truncates (wraps) input operand to fit in the output type
+template< typename Output, typename Input >
+BOOST_FORCEINLINE Output integral_extend(Input input, atomics::detail::false_type) BOOST_NOEXCEPT
+{
+    return atomics::detail::zero_extend< Output >(input);
+}
+
+//! Sign- or zero-extends or truncates (wraps) input operand to fit in the output type
+template< bool Signed, typename Output, typename Input >
+BOOST_FORCEINLINE Output integral_extend(Input input) BOOST_NOEXCEPT
+{
+    return atomics::detail::integral_extend< Output >(input, atomics::detail::integral_constant< bool, Signed >());
+}
+
+} // namespace detail
+} // namespace atomics
+} // namespace boost
+
+#endif // BOOST_ATOMIC_DETAIL_INTEGRAL_EXTEND_HPP_INCLUDED_