libcruft-util/pointer.hpp

/*
 * 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/.
 *
 * Copyright 2011-2019 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include <type_traits>
#include <cstddef>
#include <cstdint>


namespace cruft::align {
    ///////////////////////////////////////////////////////////////////////////
    /// round the pointer upwards to satisfy the provided alignment
    constexpr inline uintptr_t
    up (uintptr_t ptr, size_t alignment)
    {
        // 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;
    }


    ///////////////////////////////////////////////////////////////////////////
    /// round the pointer upwards to satisfy the provided alignment
    template <typename T>
    constexpr T*
    up (T *ptr, size_t alignment)
    {
        // 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)
        );
    }


    //-------------------------------------------------------------------------
    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);
    }


    ///------------------------------------------------------------------------
    /// round the pointer upwards to the nearest valid alignment for T
    template <typename T>
    constexpr auto
    up (T *t)
    {
        return up (t, alignof (T));
    }


    ///------------------------------------------------------------------------
    /// round the pointer upwards to the nearest valid alignment for T
    template <typename T>
    constexpr auto
    up (uintptr_t ptr)
    {
        return up (ptr, alignof (T));
    }


    ///////////////////////////////////////////////////////////////////////////
    constexpr inline uintptr_t
    down (uintptr_t ptr, size_t alignment)
    {
        return ptr - ptr % alignment;
    }


    //-------------------------------------------------------------------------
    template <typename T>
    constexpr T*
    down (T *ptr, size_t alignment)
    {
        return reinterpret_cast<T*> (
            down (reinterpret_cast<uintptr_t> (ptr), alignment)
        );
    }
}