489 lines
20 KiB
C++
489 lines
20 KiB
C++
// boost/endian/conversion.hpp -------------------------------------------------------//
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// Copyright Beman Dawes 2010, 2011, 2014
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// Distributed under the Boost Software License, Version 1.0.
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// http://www.boost.org/LICENSE_1_0.txt
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#ifndef BOOST_ENDIAN_CONVERSION_HPP
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#define BOOST_ENDIAN_CONVERSION_HPP
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#include <boost/config.hpp>
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#include <boost/predef/detail/endian_compat.h>
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#include <boost/cstdint.hpp>
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#include <boost/endian/detail/intrinsic.hpp>
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#include <boost/core/scoped_enum.hpp>
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#include <boost/static_assert.hpp>
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#include <algorithm>
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#include <cstring> // for memcpy
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//------------------------------------- synopsis ---------------------------------------//
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namespace boost
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{
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namespace endian
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{
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BOOST_SCOPED_ENUM_START(order)
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{
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big, little,
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# ifdef BOOST_BIG_ENDIAN
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native = big
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# else
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native = little
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# endif
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}; BOOST_SCOPED_ENUM_END
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//--------------------------------------------------------------------------------------//
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// //
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// return-by-value interfaces //
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// suggested by Phil Endecott //
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// //
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// user-defined types (UDTs) //
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// //
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// All return-by-value conversion function templates are required to be implemented in //
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// terms of an unqualified call to "endian_reverse(x)", a function returning the //
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// value of x with endianness reversed. This provides a customization point for any //
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// UDT that provides a "endian_reverse" free-function meeting the requirements. //
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// It must be defined in the same namespace as the UDT itself so that it will be found //
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// by argument dependent lookup (ADL). //
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// //
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//--------------------------------------------------------------------------------------//
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// customization for exact-length arithmetic types. See doc/conversion.html/#FAQ.
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// Note: The omission of a overloads for the arithmetic type (typically long, or
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// long long) not assigned to one of the exact length typedefs is a deliberate
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// design decision. Such overloads would be non-portable and thus error prone.
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inline int8_t endian_reverse(int8_t x) BOOST_NOEXCEPT;
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inline int16_t endian_reverse(int16_t x) BOOST_NOEXCEPT;
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inline int32_t endian_reverse(int32_t x) BOOST_NOEXCEPT;
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inline int64_t endian_reverse(int64_t x) BOOST_NOEXCEPT;
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inline uint8_t endian_reverse(uint8_t x) BOOST_NOEXCEPT;
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inline uint16_t endian_reverse(uint16_t x) BOOST_NOEXCEPT;
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inline uint32_t endian_reverse(uint32_t x) BOOST_NOEXCEPT;
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inline uint64_t endian_reverse(uint64_t x) BOOST_NOEXCEPT;
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// reverse byte order unless native endianness is big
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template <class EndianReversible >
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inline EndianReversible big_to_native(EndianReversible x) BOOST_NOEXCEPT;
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// Returns: x if native endian order is big, otherwise endian_reverse(x)
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template <class EndianReversible >
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inline EndianReversible native_to_big(EndianReversible x) BOOST_NOEXCEPT;
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// Returns: x if native endian order is big, otherwise endian_reverse(x)
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// reverse byte order unless native endianness is little
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template <class EndianReversible >
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inline EndianReversible little_to_native(EndianReversible x) BOOST_NOEXCEPT;
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// Returns: x if native endian order is little, otherwise endian_reverse(x)
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template <class EndianReversible >
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inline EndianReversible native_to_little(EndianReversible x) BOOST_NOEXCEPT;
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// Returns: x if native endian order is little, otherwise endian_reverse(x)
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// generic conditional reverse byte order
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template <BOOST_SCOPED_ENUM(order) From, BOOST_SCOPED_ENUM(order) To,
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class EndianReversible>
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inline EndianReversible conditional_reverse(EndianReversible from) BOOST_NOEXCEPT;
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// Returns: If From == To have different values, from.
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// Otherwise endian_reverse(from).
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// Remarks: The From == To test, and as a consequence which form the return takes, is
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// is determined at compile time.
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// runtime conditional reverse byte order
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template <class EndianReversible >
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inline EndianReversible conditional_reverse(EndianReversible from,
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BOOST_SCOPED_ENUM(order) from_order, BOOST_SCOPED_ENUM(order) to_order)
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BOOST_NOEXCEPT;
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// Returns: from_order == to_order ? from : endian_reverse(from).
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//------------------------------------------------------------------------------------//
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// Q: What happened to bswap, htobe, and the other synonym functions based on names
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// popularized by BSD, OS X, and Linux?
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// A: Turned out these may be implemented as macros on some systems. Ditto POSIX names
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// for such functionality. Since macros would cause endless problems with functions
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// of the same names, and these functions are just synonyms anyhow, they have been
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// removed.
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//------------------------------------------------------------------------------------//
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// //
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// reverse in place interfaces //
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// //
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// user-defined types (UDTs) //
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// //
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// All reverse in place function templates are required to be implemented in terms //
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// of an unqualified call to "endian_reverse_inplace(x)", a function reversing //
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// the endianness of x, which is a non-const reference. This provides a //
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// customization point for any UDT that provides a "reverse_inplace" free-function //
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// meeting the requirements. The free-function must be declared in the same //
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// namespace as the UDT itself so that it will be found by argument-dependent //
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// lookup (ADL). //
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// //
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//------------------------------------------------------------------------------------//
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// reverse in place
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template <class EndianReversible>
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inline void endian_reverse_inplace(EndianReversible& x) BOOST_NOEXCEPT;
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// Effects: x = endian_reverse(x)
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// reverse in place unless native endianness is big
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template <class EndianReversibleInplace>
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inline void big_to_native_inplace(EndianReversibleInplace& x) BOOST_NOEXCEPT;
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// Effects: none if native byte-order is big, otherwise endian_reverse_inplace(x)
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template <class EndianReversibleInplace>
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inline void native_to_big_inplace(EndianReversibleInplace& x) BOOST_NOEXCEPT;
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// Effects: none if native byte-order is big, otherwise endian_reverse_inplace(x)
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// reverse in place unless native endianness is little
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template <class EndianReversibleInplace>
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inline void little_to_native_inplace(EndianReversibleInplace& x) BOOST_NOEXCEPT;
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// Effects: none if native byte-order is little, otherwise endian_reverse_inplace(x);
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template <class EndianReversibleInplace>
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inline void native_to_little_inplace(EndianReversibleInplace& x) BOOST_NOEXCEPT;
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// Effects: none if native byte-order is little, otherwise endian_reverse_inplace(x);
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// generic conditional reverse in place
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template <BOOST_SCOPED_ENUM(order) From, BOOST_SCOPED_ENUM(order) To,
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class EndianReversibleInplace>
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inline void conditional_reverse_inplace(EndianReversibleInplace& x) BOOST_NOEXCEPT;
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// runtime reverse in place
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template <class EndianReversibleInplace>
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inline void conditional_reverse_inplace(EndianReversibleInplace& x,
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BOOST_SCOPED_ENUM(order) from_order, BOOST_SCOPED_ENUM(order) to_order)
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BOOST_NOEXCEPT;
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//----------------------------------- end synopsis -------------------------------------//
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namespace detail
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{
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// generic reverse function template implementation approach using std::reverse
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// suggested by Mathias Gaunard. Primary motivation for inclusion is to have an
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// independent implementation to test against.
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template <class T>
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inline T std_endian_reverse(T x) BOOST_NOEXCEPT
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{
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T tmp(x);
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std::reverse(
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reinterpret_cast<unsigned char*>(&tmp),
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reinterpret_cast<unsigned char*>(&tmp) + sizeof(T));
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return tmp;
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}
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// conditional unaligned reverse copy, patterned after std::reverse_copy
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template <class T>
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inline void big_reverse_copy(T from, char* to) BOOST_NOEXCEPT;
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template <class T>
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inline void big_reverse_copy(const char* from, T& to) BOOST_NOEXCEPT;
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template <class T>
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inline void little_reverse_copy(T from, char* to) BOOST_NOEXCEPT;
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template <class T>
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inline void little_reverse_copy(const char* from, T& to) BOOST_NOEXCEPT;
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} // namespace detail
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//--------------------------------------------------------------------------------------//
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// //
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// return-by-value implementation //
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// //
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// -- portable approach suggested by tymofey, with avoidance of undefined behavior //
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// as suggested by Giovanni Piero Deretta, with a further refinement suggested //
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// by Pyry Jahkola. //
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// -- intrinsic approach suggested by reviewers, and by David Stone, who provided //
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// his Boost licensed macro implementation (detail/intrinsic.hpp) //
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// //
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//--------------------------------------------------------------------------------------//
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inline int8_t endian_reverse(int8_t x) BOOST_NOEXCEPT
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{
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return x;
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}
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inline int16_t endian_reverse(int16_t x) BOOST_NOEXCEPT
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{
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# ifdef BOOST_ENDIAN_NO_INTRINSICS
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return (static_cast<uint16_t>(x) << 8)
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# else
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return BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_2(static_cast<uint16_t>(x));
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# endif
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}
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inline int32_t endian_reverse(int32_t x) BOOST_NOEXCEPT
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{
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# ifdef BOOST_ENDIAN_NO_INTRINSICS
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uint32_t step16;
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step16 = static_cast<uint32_t>(x) << 16 | static_cast<uint32_t>(x) >> 16;
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return
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((static_cast<uint32_t>(step16) << 8) & 0xff00ff00)
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| ((static_cast<uint32_t>(step16) >> 8) & 0x00ff00ff);
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# else
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return BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(static_cast<uint32_t>(x));
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# endif
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}
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inline int64_t endian_reverse(int64_t x) BOOST_NOEXCEPT
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{
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# ifdef BOOST_ENDIAN_NO_INTRINSICS
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uint64_t step32, step16;
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step32 = static_cast<uint64_t>(x) << 32 | static_cast<uint64_t>(x) >> 32;
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step16 = (step32 & 0x0000FFFF0000FFFFULL) << 16
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return static_cast<int64_t>((step16 & 0x00FF00FF00FF00FFULL) << 8
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| (step16 & 0xFF00FF00FF00FF00ULL) >> 8);
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# else
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return BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(static_cast<uint64_t>(x));
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# endif
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}
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inline uint8_t endian_reverse(uint8_t x) BOOST_NOEXCEPT
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{
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return x;
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}
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inline uint16_t endian_reverse(uint16_t x) BOOST_NOEXCEPT
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{
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# ifdef BOOST_ENDIAN_NO_INTRINSICS
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return (x << 8)
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| (x >> 8);
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# else
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return BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_2(x);
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# endif
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}
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inline uint32_t endian_reverse(uint32_t x) BOOST_NOEXCEPT
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{
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# ifdef BOOST_ENDIAN_NO_INTRINSICS
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uint32_t step16;
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step16 = x << 16 | x >> 16;
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return
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((step16 << 8) & 0xff00ff00)
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| ((step16 >> 8) & 0x00ff00ff);
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# else
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return BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(x);
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# endif
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}
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inline uint64_t endian_reverse(uint64_t x) BOOST_NOEXCEPT
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{
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# ifdef BOOST_ENDIAN_NO_INTRINSICS
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uint64_t step32, step16;
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step32 = x << 32 | x >> 32;
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step16 = (step32 & 0x0000FFFF0000FFFFULL) << 16
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| (step32 & 0xFFFF0000FFFF0000ULL) >> 16;
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return (step16 & 0x00FF00FF00FF00FFULL) << 8
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| (step16 & 0xFF00FF00FF00FF00ULL) >> 8;
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# else
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return BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(x);
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# endif
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}
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template <class EndianReversible >
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inline EndianReversible big_to_native(EndianReversible x) BOOST_NOEXCEPT
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{
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# ifdef BOOST_BIG_ENDIAN
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return x;
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# else
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return endian_reverse(x);
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# endif
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}
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template <class EndianReversible >
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inline EndianReversible native_to_big(EndianReversible x) BOOST_NOEXCEPT
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{
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# ifdef BOOST_BIG_ENDIAN
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return x;
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# else
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return endian_reverse(x);
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# endif
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}
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template <class EndianReversible >
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inline EndianReversible little_to_native(EndianReversible x) BOOST_NOEXCEPT
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{
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# ifdef BOOST_LITTLE_ENDIAN
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return x;
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# else
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return endian_reverse(x);
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# endif
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}
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template <class EndianReversible >
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inline EndianReversible native_to_little(EndianReversible x) BOOST_NOEXCEPT
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{
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# ifdef BOOST_LITTLE_ENDIAN
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return x;
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# else
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return endian_reverse(x);
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# endif
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}
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namespace detail
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{
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// Primary template and specializations to support endian_reverse().
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// See rationale in endian_reverse() below.
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template <BOOST_SCOPED_ENUM(order) From, BOOST_SCOPED_ENUM(order) To,
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class EndianReversible>
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class value_converter ; // primary template
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template <class T> class value_converter <order::big, order::big, T>
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{public: T operator()(T x) BOOST_NOEXCEPT {return x;}};
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template <class T> class value_converter <order::little, order::little, T>
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{public: T operator()(T x) BOOST_NOEXCEPT {return x;}};
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template <class T> class value_converter <order::big, order::little, T>
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{public: T operator()(T x) BOOST_NOEXCEPT {return endian_reverse(x);}};
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template <class T> class value_converter <order::little, order::big, T>
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{public: T operator()(T x) BOOST_NOEXCEPT {return endian_reverse(x);}};
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}
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// generic conditional reverse
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template <BOOST_SCOPED_ENUM(order) From, BOOST_SCOPED_ENUM(order) To,
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class EndianReversible>
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inline EndianReversible conditional_reverse(EndianReversible from) BOOST_NOEXCEPT {
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// work around lack of function template partial specialization by instantiating
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// a function object of a class that is partially specialized on the two order
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// template parameters, and then calling its operator().
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detail::value_converter <From, To, EndianReversible> tmp;
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return tmp(from);
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}
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// runtime conditional reverse
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template <class EndianReversible >
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inline EndianReversible conditional_reverse(EndianReversible from,
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BOOST_SCOPED_ENUM(order) from_order, BOOST_SCOPED_ENUM(order) to_order) BOOST_NOEXCEPT
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{
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return from_order == to_order ? from : endian_reverse(from);
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}
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//--------------------------------------------------------------------------------------//
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// reverse-in-place implementation //
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//--------------------------------------------------------------------------------------//
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// reverse in place
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template <class EndianReversible>
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inline void endian_reverse_inplace(EndianReversible& x) BOOST_NOEXCEPT
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{
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x = endian_reverse(x);
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}
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template <class EndianReversibleInplace>
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# ifdef BOOST_BIG_ENDIAN
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inline void big_to_native_inplace(EndianReversibleInplace&) BOOST_NOEXCEPT {}
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# else
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inline void big_to_native_inplace(EndianReversibleInplace& x) BOOST_NOEXCEPT
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{ endian_reverse_inplace(x); }
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# endif
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template <class EndianReversibleInplace>
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# ifdef BOOST_BIG_ENDIAN
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inline void native_to_big_inplace(EndianReversibleInplace&) BOOST_NOEXCEPT {}
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# else
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inline void native_to_big_inplace(EndianReversibleInplace& x) BOOST_NOEXCEPT
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{
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endian_reverse_inplace(x);
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}
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# endif
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template <class EndianReversibleInplace>
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# ifdef BOOST_LITTLE_ENDIAN
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inline void little_to_native_inplace(EndianReversibleInplace&) BOOST_NOEXCEPT {}
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# else
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inline void little_to_native_inplace(EndianReversibleInplace& x) BOOST_NOEXCEPT
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{ endian_reverse_inplace(x); }
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# endif
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template <class EndianReversibleInplace>
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# ifdef BOOST_LITTLE_ENDIAN
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inline void native_to_little_inplace(EndianReversibleInplace&) BOOST_NOEXCEPT {}
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# else
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inline void native_to_little_inplace(EndianReversibleInplace& x) BOOST_NOEXCEPT
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{
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endian_reverse_inplace(x);
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}
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# endif
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namespace detail
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{
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// Primary template and specializations support generic
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// endian_reverse_inplace().
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// See rationale in endian_reverse_inplace() below.
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template <BOOST_SCOPED_ENUM(order) From, BOOST_SCOPED_ENUM(order) To,
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class EndianReversibleInplace>
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class converter; // primary template
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template <class T> class converter<order::big, order::big, T>
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{public: void operator()(T&) BOOST_NOEXCEPT {/*no effect*/}};
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template <class T> class converter<order::little, order::little, T>
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{public: void operator()(T&) BOOST_NOEXCEPT {/*no effect*/}};
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template <class T> class converter<order::big, order::little, T>
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{public: void operator()(T& x) BOOST_NOEXCEPT { endian_reverse_inplace(x); }};
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template <class T> class converter<order::little, order::big, T>
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{public: void operator()(T& x) BOOST_NOEXCEPT { endian_reverse_inplace(x); }};
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} // namespace detail
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// generic conditional reverse in place
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template <BOOST_SCOPED_ENUM(order) From, BOOST_SCOPED_ENUM(order) To,
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class EndianReversibleInplace>
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inline void conditional_reverse_inplace(EndianReversibleInplace& x) BOOST_NOEXCEPT
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{
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// work around lack of function template partial specialization by instantiating
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// a function object of a class that is partially specialized on the two order
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// template parameters, and then calling its operator().
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detail::converter<From, To, EndianReversibleInplace> tmp;
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tmp(x); // call operator ()
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}
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// runtime reverse in place
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template <class EndianReversibleInplace>
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inline void conditional_reverse_inplace(EndianReversibleInplace& x,
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BOOST_SCOPED_ENUM(order) from_order, BOOST_SCOPED_ENUM(order) to_order)
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BOOST_NOEXCEPT
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{
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if (from_order != to_order)
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endian_reverse_inplace(x);
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}
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namespace detail
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{
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template <class T>
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inline void big_reverse_copy(T from, char* to) BOOST_NOEXCEPT
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{
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# ifdef BOOST_BIG_ENDIAN
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std::memcpy(to, reinterpret_cast<const char*>(&from), sizeof(T));
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# else
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std::reverse_copy(reinterpret_cast<const char*>(&from),
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reinterpret_cast<const char*>(&from) + sizeof(T), to);
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# endif
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}
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template <class T>
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inline void big_reverse_copy(const char* from, T& to) BOOST_NOEXCEPT
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{
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# ifdef BOOST_BIG_ENDIAN
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std::memcpy(reinterpret_cast<char*>(&to), from, sizeof(T));
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# else
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std::reverse_copy(from, from + sizeof(T), reinterpret_cast<char*>(&to));
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# endif
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}
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template <class T>
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inline void little_reverse_copy(T from, char* to) BOOST_NOEXCEPT
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{
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# ifdef BOOST_LITTLE_ENDIAN
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std::memcpy(to, reinterpret_cast<const char*>(&from), sizeof(T));
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# else
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|
std::reverse_copy(reinterpret_cast<const char*>(&from),
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reinterpret_cast<const char*>(&from) + sizeof(T), to);
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# endif
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|
}
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|
template <class T>
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inline void little_reverse_copy(const char* from, T& to) BOOST_NOEXCEPT
|
|
{
|
|
# ifdef BOOST_LITTLE_ENDIAN
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|
std::memcpy(reinterpret_cast<char*>(&to), from, sizeof(T));
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|
# else
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|
std::reverse_copy(from, from + sizeof(T), reinterpret_cast<char*>(&to));
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|
# endif
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|
}
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|
} // namespace detail
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|
} // namespace endian
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|
} // namespace boost
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|
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#endif // BOOST_ENDIAN_CONVERSION_HPP
|