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boost/endian/detail/intrinsic.hpp

//  endian/detail/intrinsic.hpp  -------------------------------------------------------//

//  Copyright (C) 2012 David Stone
//  Copyright Beman Dawes 2013

//  Distributed under the Boost Software License, Version 1.0.
//  http://www.boost.org/LICENSE_1_0.txt

#ifndef BOOST_ENDIAN_INTRINSIC_HPP
#define BOOST_ENDIAN_INTRINSIC_HPP

//  Allow user to force BOOST_ENDIAN_NO_INTRINSICS in case they aren't available for a
//  particular platform/compiler combination. Please report such platform/compiler
//  combinations to the Boost mailing list.
#ifndef BOOST_ENDIAN_NO_INTRINSICS

#ifndef __has_builtin         // Optional of course
  #define __has_builtin(x) 0  // Compatibility with non-clang compilers
#endif

#if defined(_MSC_VER)
//  Microsoft documents these as being compatible since Windows 95 and specifically
//  lists runtime library support since Visual Studio 2003 (aka 7.1).
//  Clang/c2 uses the Microsoft rather than GCC intrinsics, so we check for
//  defined(_MSC_VER) before defined(__clang__)
# define BOOST_ENDIAN_INTRINSIC_MSG "cstdlib _byteswap_ushort, etc."
# include <cstdlib>
# define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_2(x) _byteswap_ushort(x)
# define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(x) _byteswap_ulong(x)
# define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(x) _byteswap_uint64(x)

//  GCC and Clang recent versions provide intrinsic byte swaps via builtins
#elif (defined(__clang__) && __has_builtin(__builtin_bswap32) && __has_builtin(__builtin_bswap64)) \
  || (defined(__GNUC__ ) && \
  (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)))
# define BOOST_ENDIAN_INTRINSIC_MSG "__builtin_bswap16, etc."
// prior to 4.8, gcc did not provide __builtin_bswap16 on some platforms so we emulate it
// see http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52624
// Clang has a similar problem, but their feature test macros make it easier to detect
# if (defined(__clang__) && __has_builtin(__builtin_bswap16)) \
  || (defined(__GNUC__) &&(__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8)))
#   define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_2(x) __builtin_bswap16(x)
# else
#   define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_2(x) __builtin_bswap32((x) << 16)
# endif
# define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(x) __builtin_bswap32(x)
# define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(x) __builtin_bswap64(x)

//  Linux systems provide the byteswap.h header, with 
#elif defined(__linux__)
//  don't check for obsolete forms defined(linux) and defined(__linux) on the theory that
//  compilers that predefine only these are so old that byteswap.h probably isn't present.
# define BOOST_ENDIAN_INTRINSIC_MSG "byteswap.h bswap_16, etc."
# include <byteswap.h>
# define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_2(x) bswap_16(x)
# define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(x) bswap_32(x)
# define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(x) bswap_64(x)

#else
# define BOOST_ENDIAN_NO_INTRINSICS
# define BOOST_ENDIAN_INTRINSIC_MSG "no byte swap intrinsics"
#endif

#elif !defined(BOOST_ENDIAN_INTRINSIC_MSG)
# define BOOST_ENDIAN_INTRINSIC_MSG "no byte swap intrinsics"
#endif  // BOOST_ENDIAN_NO_INTRINSICS
#endif  // BOOST_ENDIAN_INTRINSIC_HPP