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Use __builtin_bit_cast when available

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This commit is contained in:
Peter Dimov 2023-06-01 02:38:57 +03:00
parent 85527c4045
commit 5a3b4df5de
3 changed files with 47 additions and 0 deletions
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22
include/boost/core/bit.hpp
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@ -43,6 +43,16 @@
# define BOOST_CORE_HAS_BUILTIN_ISCONSTEVAL
#endif
#if defined(__has_builtin)
# if __has_builtin(__builtin_bit_cast)
# define BOOST_CORE_HAS_BUILTIN_BIT_CAST
# endif
#endif
#if defined(BOOST_MSVC) && BOOST_MSVC >= 1926
# define BOOST_CORE_HAS_BUILTIN_BIT_CAST
#endif
namespace boost
{
namespace core
@ -50,6 +60,16 @@ namespace core
// bit_cast
#if defined(BOOST_CORE_HAS_BUILTIN_BIT_CAST)
template<class To, class From>
BOOST_CONSTEXPR To bit_cast( From const & from ) BOOST_NOEXCEPT
{
return __builtin_bit_cast( To, from );
}
#else
template<class To, class From>
To bit_cast( From const & from ) BOOST_NOEXCEPT
{
@ -60,6 +80,8 @@ To bit_cast( From const & from ) BOOST_NOEXCEPT
return to;
}
#endif
// countl
#if defined(__GNUC__) || defined(__clang__)

1
test/Jamfile.v2
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@ -304,6 +304,7 @@ run bit_byteswap_test.cpp
compile-fail bit_width_fail.cpp
: <warnings>off ;
compile bit_cast_test_cx.cpp ;
compile bit_rotate_test_cx.cpp ;
compile bit_countr_test_cx.cpp ;
compile bit_countl_test_cx.cpp ;

24
test/bit_cast_test_cx.cpp Normal file
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@ -0,0 +1,24 @@
// constexpr test for boost/core/bit.hpp (bit_cast)
//
// Copyright 2023 Peter Dimov
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt
#include <boost/config.hpp>
#include <boost/config/pragma_message.hpp>
#if defined(BOOST_NO_CXX11_CONSTEXPR)
BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX11_CONSTEXPR is defined" )
#else
#include <boost/core/bit.hpp>
#include <boost/cstdint.hpp>
#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
STATIC_ASSERT( boost::core::bit_cast<boost::uint32_t>( 1.0f ) == 0x3F800000u );
STATIC_ASSERT( boost::core::bit_cast<boost::uint64_t>( 1.0 ) == 0x3FF0000000000000ull );
#endif