83 lines
2.7 KiB
C++
83 lines
2.7 KiB
C++
/////////////////////////////////////////////////////////////////////////////
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//
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// (C) Copyright Ion Gaztanaga 2007-2012
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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_BITS_HPP
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#define BOOST_INTRUSIVE_POINTER_PLUS_BITS_HPP
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#include <boost/intrusive/detail/mpl.hpp> //ls_zeros
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#include <boost/intrusive/detail/assert.hpp> //BOOST_INTRUSIVE_INVARIANT_ASSERT
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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 extra bits 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 max_pointer_plus_bits
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{
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static const std::size_t value = 0;
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};
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//!This is a specialization for raw pointers.
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//!Raw pointers can embed extra bits in the lower bits
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//!if the alignment is multiple of 2pow(NumBits).
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template<std::size_t Alignment>
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struct max_pointer_plus_bits<void*, Alignment>
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{
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static const std::size_t value = detail::ls_zeros<Alignment>::value;
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};
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//!This is class that is supposed to have static methods
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//!to embed extra bits 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 bits 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_bits<>::value is non-zero can make use of these
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//!operations to embed the bits in the pointer.
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template<class Pointer, std::size_t NumBits>
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struct pointer_plus_bits;
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//!This is the specialization to embed extra bits of information
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//!in a raw pointer. The extra bits are stored in the lower bits of the pointer.
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template<class T, std::size_t NumBits>
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struct pointer_plus_bits<T*, NumBits>
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{
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static const std::size_t Mask = ((std::size_t(1u) << NumBits) - 1);
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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) & ~Mask); }
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static void set_pointer(pointer &n, pointer p)
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{
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BOOST_INTRUSIVE_INVARIANT_ASSERT(0 == (std::size_t(p) & Mask));
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n = pointer(std::size_t(p) | (std::size_t(n) & Mask));
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}
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static std::size_t get_bits(pointer n)
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{ return (std::size_t(n) & Mask); }
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static void set_bits(pointer &n, std::size_t c)
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{
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BOOST_INTRUSIVE_INVARIANT_ASSERT(c <= Mask);
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n = pointer(std::size_t(get_pointer(n)) | c);
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}
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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_BITS_HPP
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