boost/endian/detail/endian_reverse.hpp

   1 #ifndef BOOST_ENDIAN_DETAIL_ENDIAN_REVERSE_HPP_INCLUDED
   2 #define BOOST_ENDIAN_DETAIL_ENDIAN_REVERSE_HPP_INCLUDED
   3
   4 // Copyright 2019 Peter Dimov
   5 //
   6 // Distributed under the Boost Software License, Version 1.0.
   7 // http://www.boost.org/LICENSE_1_0.txt
   8
   9 #include <boost/endian/detail/integral_by_size.hpp>
  10 #include <boost/endian/detail/intrinsic.hpp>
  11 #include <boost/type_traits/is_integral.hpp>
  12 #include <boost/type_traits/is_same.hpp>
  13 #include <boost/static_assert.hpp>
  14 #include <boost/cstdint.hpp>
  15 #include <boost/config.hpp>
  16 #include <cstddef>
  17 #include <cstring>
  18
  19 #if defined(BOOST_ENDIAN_NO_INTRINSICS)
  20 # if defined(BOOST_NO_CXX14_CONSTEXPR)
  21 #  define BOOST_ENDIAN_CONSTEXPR
  22 # else
  23 #  define BOOST_ENDIAN_CONSTEXPR constexpr
  24 # endif
  25 #else
  26 # if defined(BOOST_ENDIAN_CONSTEXPR_INTRINSICS)
  27 #  define BOOST_ENDIAN_CONSTEXPR BOOST_CONSTEXPR
  28 # else
  29 #  define BOOST_ENDIAN_CONSTEXPR
  30 # endif
  31 #endif
  32
  33 namespace boost
  34 {
  35 namespace endian
  36 {
  37
  38 namespace detail
  39 {
  40
  41 //  -- portable approach suggested by tymofey, with avoidance of undefined behavior
  42 //     as suggested by Giovanni Piero Deretta, with a further refinement suggested
  43 //     by Pyry Jahkola.
  44 //  -- intrinsic approach suggested by reviewers, and by David Stone, who provided
  45 //     his Boost licensed macro implementation (detail/intrinsic.hpp)
  46
  47 inline uint8_t BOOST_CONSTEXPR endian_reverse_impl( uint8_t x ) BOOST_NOEXCEPT
  48 {
  49     return x;
  50 }
  51
  52 inline uint16_t BOOST_ENDIAN_CONSTEXPR endian_reverse_impl( uint16_t x ) BOOST_NOEXCEPT
  53 {
  54 #ifdef BOOST_ENDIAN_NO_INTRINSICS
  55
  56     return (x << 8) | (x >> 8);
  57
  58 #else
  59
  60     return BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_2(x);
  61
  62 #endif
  63 }
  64
  65 inline uint32_t BOOST_ENDIAN_CONSTEXPR endian_reverse_impl( uint32_t x ) BOOST_NOEXCEPT
  66 {
  67 #ifdef BOOST_ENDIAN_NO_INTRINSICS
  68
  69     uint32_t step16 = x << 16 | x >> 16;
  70     return ((step16 << 8) & 0xff00ff00) | ((step16 >> 8) & 0x00ff00ff);
  71
  72 #else
  73
  74     return BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(x);
  75
  76 #endif
  77 }
  78
  79 inline uint64_t BOOST_ENDIAN_CONSTEXPR endian_reverse_impl( uint64_t x ) BOOST_NOEXCEPT
  80 {
  81 #ifdef BOOST_ENDIAN_NO_INTRINSICS
  82
  83     uint64_t step32 = x << 32 | x >> 32;
  84     uint64_t step16 = (step32 & 0x0000FFFF0000FFFFULL) << 16 | (step32 & 0xFFFF0000FFFF0000ULL) >> 16;
  85     return (step16 & 0x00FF00FF00FF00FFULL) << 8 | (step16 & 0xFF00FF00FF00FF00ULL) >> 8;
  86
  87 #else
  88
  89     return BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(x);
  90
  91 # endif
  92 }
  93
  94 #if defined(BOOST_HAS_INT128)
  95
  96 inline uint128_type BOOST_ENDIAN_CONSTEXPR endian_reverse_impl( uint128_type x ) BOOST_NOEXCEPT
  97 {
  98     return endian_reverse_impl( static_cast<uint64_t>( x >> 64 ) ) |
  99         static_cast<uint128_type>( endian_reverse_impl( static_cast<uint64_t>( x ) ) ) << 64;
 100 }
 101
 102 #endif
 103
 104 } // namespace detail
 105
 106 // Requires:
 107 //    T is non-bool integral
 108
 109 template<class T> inline BOOST_CONSTEXPR T endian_reverse( T x ) BOOST_NOEXCEPT
 110 {
 111     BOOST_STATIC_ASSERT( is_integral<T>::value && !(is_same<T, bool>::value) );
 112
 113     typedef typename detail::integral_by_size< sizeof(T) >::type uintN_t;
 114
 115     return static_cast<T>( detail::endian_reverse_impl( static_cast<uintN_t>( x ) ) );
 116 }
 117
 118 template <class EndianReversible>
 119 inline void endian_reverse_inplace(EndianReversible& x) BOOST_NOEXCEPT
 120 {
 121     x = endian_reverse( x );
 122 }
 123
 124 } // namespace endian
 125 } // namespace boost
 126
 127 #endif  // BOOST_ENDIAN_DETAIL_ENDIAN_REVERSE_HPP_INCLUDED