forked from boostorg/intrusive
76 lines
2.3 KiB
C++
76 lines
2.3 KiB
C++
/////////////////////////////////////////////////////////////////////////////
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//
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// (C) Copyright Ion Gaztanaga 2007
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//
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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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// See http://www.boost.org/libs/intrusive for documentation.
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//
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/////////////////////////////////////////////////////////////////////////////
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#ifndef BOOST_INTRUSIVE_POINTER_PLUS_BIT_HPP
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#define BOOST_INTRUSIVE_POINTER_PLUS_BIT_HPP
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namespace boost {
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namespace intrusive {
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//!This trait class is used to know if a pointer
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//!can embed an extra bit of information if
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//!it's going to be used to point to objects
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//!with an alignment of "Alignment" bytes.
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template<class VoidPointer, std::size_t Alignment>
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struct has_pointer_plus_bit
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{
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enum { value = false };
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};
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//!This is an specialization for raw pointers.
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//!Raw pointers can embed an extra bit in the lower bit
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//!if the alignment is multiple of 2.
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template<std::size_t N>
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struct has_pointer_plus_bit<void*, N>
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{
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enum { value = N % 2u == 0 };
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};
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//!This is class that is supposed to have static methods
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//!to embed an extra bit of information in a pointer.
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//!This is a declaration and there is no default implementation,
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//!because operations to embed the bit change with every pointer type.
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//!
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//!An implementation that detects that a pointer type whose
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//!has_pointer_plus_bit<>::value is non-zero can make use of these
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//!operations to embed the bit in the pointer.
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template<class Pointer>
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struct pointer_plus_bit;
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//!This is the specialization to embed an extra bit of information
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//!in a raw pointer. The extra bit is stored in the lower bit of the pointer.
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template<class T>
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struct pointer_plus_bit<T*>
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{
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typedef T* pointer;
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static pointer get_pointer(pointer n)
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{ return pointer(std::size_t(n) & std::size_t(~1u)); }
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static void set_pointer(pointer &n, pointer p)
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{
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assert(0 == (std::size_t(p) & std::size_t(1u)));
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n = pointer(std::size_t(p) | (std::size_t(n) & std::size_t(1u)));
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}
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static bool get_bit(pointer n)
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{ return (std::size_t(n) & std::size_t(1u)) != 0; }
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static void set_bit(pointer &n, bool c)
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{ n = pointer(std::size_t(get_pointer(n)) | std::size_t(c)); }
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};
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} //namespace intrusive
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} //namespace boost
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#endif //BOOST_INTRUSIVE_POINTER_PLUS_BIT_HPP
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