整理

include/boost/atomic/detail/memory_order_utils.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) 2020 Andrey Semashev
+ */
+/*!
+ * \file   atomic/detail/memory_order_utils.hpp
+ *
+ * This header contains utilities related to memory order constants.
+ */
+
+#ifndef BOOST_ATOMIC_DETAIL_MEMORY_ORDER_UTILS_HPP_INCLUDED_
+#define BOOST_ATOMIC_DETAIL_MEMORY_ORDER_UTILS_HPP_INCLUDED_
+
+#include <boost/memory_order.hpp>
+#include <boost/atomic/detail/config.hpp>
+#include <boost/atomic/detail/header.hpp>
+
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#pragma once
+#endif
+
+namespace boost {
+namespace atomics {
+namespace detail {
+
+BOOST_FORCEINLINE constexpr memory_order deduce_failure_order(memory_order order) noexcept
+{
+    return order == memory_order_acq_rel ? memory_order_acquire : (order == memory_order_release ? memory_order_relaxed : order);
+}
+
+BOOST_FORCEINLINE constexpr bool cas_failure_order_must_not_be_stronger_than_success_order(memory_order success_order, memory_order failure_order) noexcept
+{
+    // 15 == (memory_order_seq_cst | memory_order_consume), see memory_order.hpp
+    // Given the enum values we can test the strength of memory order requirements with this single condition.
+    return (static_cast< unsigned int >(failure_order) & 15u) <= (static_cast< unsigned int >(success_order) & 15u);
+}
+
+} // namespace detail
+} // namespace atomics
+} // namespace boost
+
+#include <boost/atomic/detail/footer.hpp>
+
+#endif // BOOST_ATOMIC_DETAIL_MEMORY_ORDER_UTILS_HPP_INCLUDED_