119 lines
4.4 KiB
C++
Executable File
119 lines
4.4 KiB
C++
Executable File
/*
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* Distributed under the Boost Software License, Version 1.0.
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* (See accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* Copyright (c) 2018, 2021 Andrey Semashev
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*/
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/*!
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* \file atomic/detail/bitwise_fp_cast.hpp
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*
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* This header defines \c bitwise_fp_cast used to convert between storage and floating point value types
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*/
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#ifndef BOOST_ATOMIC_DETAIL_BITWISE_FP_CAST_HPP_INCLUDED_
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#define BOOST_ATOMIC_DETAIL_BITWISE_FP_CAST_HPP_INCLUDED_
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#include <cstddef>
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#include <boost/atomic/detail/config.hpp>
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#include <boost/atomic/detail/float_sizes.hpp>
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#include <boost/atomic/detail/bitwise_cast.hpp>
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#if defined(BOOST_ATOMIC_DETAIL_BIT_CAST)
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#include <boost/atomic/detail/type_traits/integral_constant.hpp>
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#endif
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#include <boost/atomic/detail/header.hpp>
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#ifdef BOOST_HAS_PRAGMA_ONCE
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#pragma once
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#endif
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namespace boost {
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namespace atomics {
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namespace detail {
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/*!
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* \brief The type trait returns the size of the value of the specified floating point type
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*
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* This size may be less than <tt>sizeof(T)</tt> if the implementation uses padding bytes for a particular FP type. This is
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* often the case with 80-bit extended double, which is stored in 12 or 16 initial bytes with tail padding filled with garbage.
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*/
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template< typename T >
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struct value_size_of
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{
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static BOOST_CONSTEXPR_OR_CONST std::size_t value = sizeof(T);
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};
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#if defined(BOOST_ATOMIC_DETAIL_SIZEOF_FLOAT_VALUE)
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template< >
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struct value_size_of< float >
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{
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static BOOST_CONSTEXPR_OR_CONST std::size_t value = BOOST_ATOMIC_DETAIL_SIZEOF_FLOAT_VALUE;
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};
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#endif
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#if defined(BOOST_ATOMIC_DETAIL_SIZEOF_DOUBLE_VALUE)
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template< >
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struct value_size_of< double >
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{
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static BOOST_CONSTEXPR_OR_CONST std::size_t value = BOOST_ATOMIC_DETAIL_SIZEOF_DOUBLE_VALUE;
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};
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#endif
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#if defined(BOOST_ATOMIC_DETAIL_SIZEOF_LONG_DOUBLE_VALUE)
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template< >
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struct value_size_of< long double >
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{
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static BOOST_CONSTEXPR_OR_CONST std::size_t value = BOOST_ATOMIC_DETAIL_SIZEOF_LONG_DOUBLE_VALUE;
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};
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#endif
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template< typename T >
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struct value_size_of< const T > : value_size_of< T > {};
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template< typename T >
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struct value_size_of< volatile T > : value_size_of< T > {};
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template< typename T >
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struct value_size_of< const volatile T > : value_size_of< T > {};
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#if !defined(BOOST_ATOMIC_NO_CLEAR_PADDING)
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// BOOST_ATOMIC_DETAIL_CLEAR_PADDING, which is used in bitwise_cast, will clear the tail padding bits in the source object.
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// We don't need to specify the actual value size to avoid redundant zeroing of the tail padding.
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#define BOOST_ATOMIC_DETAIL_BITWISE_FP_CAST_VALUE_SIZE_OF(x) sizeof(x)
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#else
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#define BOOST_ATOMIC_DETAIL_BITWISE_FP_CAST_VALUE_SIZE_OF(x) atomics::detail::value_size_of< x >::value
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#endif
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#if defined(BOOST_ATOMIC_DETAIL_BIT_CAST)
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//! Similar to bitwise_cast, but either \c From or \c To is expected to be a floating point type. Attempts to detect the actual value size in the source object and considers the rest of the object as padding.
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template< typename To, typename From >
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BOOST_FORCEINLINE BOOST_ATOMIC_DETAIL_CONSTEXPR_BITWISE_CAST To bitwise_fp_cast(From const& from) BOOST_NOEXCEPT
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{
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// For floating point types, has_unique_object_representations is typically false even if the type contains no padding bits.
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// Here, we rely on our detection of the actual value size to select constexpr bit_cast implementation when possible. We assume
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// here that floating point value bits are contiguous.
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return atomics::detail::bitwise_cast_impl< To, BOOST_ATOMIC_DETAIL_BITWISE_FP_CAST_VALUE_SIZE_OF(From) >(from, atomics::detail::integral_constant< bool,
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atomics::detail::value_size_of< From >::value == sizeof(From) && atomics::detail::value_size_of< From >::value == sizeof(To) >());
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}
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#else // defined(BOOST_ATOMIC_DETAIL_BIT_CAST)
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//! Similar to bitwise_cast, but either \c From or \c To is expected to be a floating point type. Attempts to detect the actual value size in the source object and considers the rest of the object as padding.
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template< typename To, typename From >
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BOOST_FORCEINLINE BOOST_ATOMIC_DETAIL_CONSTEXPR_BITWISE_CAST To bitwise_fp_cast(From const& from) BOOST_NOEXCEPT
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{
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return atomics::detail::bitwise_cast< To, BOOST_ATOMIC_DETAIL_BITWISE_FP_CAST_VALUE_SIZE_OF(From) >(from);
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}
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#endif // defined(BOOST_ATOMIC_DETAIL_BIT_CAST)
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} // namespace detail
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} // namespace atomics
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} // namespace boost
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#include <boost/atomic/detail/footer.hpp>
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#endif // BOOST_ATOMIC_DETAIL_BITWISE_FP_CAST_HPP_INCLUDED_
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