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 2011-2017 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include <cstddef>
#include <cstdint>


namespace cruft {
    ///////////////////////////////////////////////////////////////////////////
    /// round the pointer upwards to satisfy the provided alignment
    constexpr inline uintptr_t
    align_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*
    align_up (T *_ptr, size_t alignment)
    {
        // we perform this as two steps to avoid unnecessarily incrementing when
        // remainder is zero.
        return reinterpret_cast<T*>(
            align_up (reinterpret_cast<uintptr_t> (_ptr), alignment)
        );
    }


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


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


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


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