libcruft-util/pointer.hpp

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/*
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* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
* Copyright 2011-2019 Danny Robson <danny@nerdcruft.net>
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*/
#pragma once
#include <utility>
#include <type_traits>
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#include <cstddef>
#include <cstdint>
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namespace cruft::ptr {
/// A utiliity function that deletes the provided pointer.
///
/// Useful as a means of moving `delete` calls inside a translation unit
/// and hence removing the need to include implementation headers for a
/// type that needs deletion.
template <typename ValueT>
void destroy (ValueT*);
/// A smart pointer that defers deletion to `destroy`.
///
/// This is solely useful as a way of avoid undefined type errors when
/// using std::unique_ptr and forward declarations.
template <typename ValueT>
class thin {
public:
explicit thin (ValueT *_value) { m_value = _value; }
~thin () { destroy (m_value); }
thin (thin const&) = delete;
thin& operator= (thin const&) = delete;
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thin (thin &&rhs) noexcept
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: m_value (rhs.m_value)
{ rhs.m_value = nullptr; }
thin& operator= (thin &&rhs) noexcept
{
std::swap (m_value, rhs.m_value);
}
ValueT & operator* (void) &{ return *m_value; }
ValueT const& operator* (void) const &{ return *m_value; }
ValueT * operator->(void) &{ return m_value; }
ValueT const* operator->(void) const &{ return m_value; }
private:
ValueT *m_value;
};
template <typename ValueT, typename ...ArgsT>
thin<ValueT>
make_thin (ArgsT &&...args)
{
return thin (new ValueT (std::forward<ArgsT> (args)...));
}
}
namespace cruft::align {
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///////////////////////////////////////////////////////////////////////////
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/// round the pointer upwards to satisfy the provided alignment
constexpr inline uintptr_t
up (uintptr_t ptr, size_t alignment)
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{
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// we perform this as two steps to avoid unnecessarily incrementing when
// remainder is zero.
if (auto mod = ptr % alignment; mod)
ptr += alignment - mod;
return ptr;
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}
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///////////////////////////////////////////////////////////////////////////
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/// round the pointer upwards to satisfy the provided alignment
template <typename T>
constexpr T*
up (T *ptr, size_t alignment)
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{
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// we perform this as two steps to avoid unnecessarily incrementing when
// remainder is zero.
return reinterpret_cast<T*>(
up (reinterpret_cast<uintptr_t> (ptr), alignment)
);
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}
//-------------------------------------------------------------------------
template <typename T>
constexpr T*
up (T *ptr, std::align_val_t _alignment)
{
auto alignment = std::underlying_type_t<decltype(_alignment)> (_alignment);
return up (ptr, alignment);
}
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///------------------------------------------------------------------------
/// round the pointer upwards to the nearest valid alignment for T
template <typename T>
constexpr auto
up (T *t)
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{
return up (t, alignof (T));
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}
///------------------------------------------------------------------------
/// round the pointer upwards to the nearest valid alignment for T
template <typename T>
constexpr auto
up (uintptr_t ptr)
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{
return up (ptr, alignof (T));
}
///////////////////////////////////////////////////////////////////////////
constexpr inline uintptr_t
down (uintptr_t ptr, size_t alignment)
{
return ptr - ptr % alignment;
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}
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//-------------------------------------------------------------------------
template <typename T>
constexpr T*
down (T *ptr, size_t alignment)
{
return reinterpret_cast<T*> (
down (reinterpret_cast<uintptr_t> (ptr), alignment)
);
}
}