ladybird/AK/CircularDeque.h

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include <AK/CircularQueue.h>
#include <AK/Types.h>

namespace AK {

template<typename T, size_t Capacity>
class CircularDeque : public CircularQueue<T, Capacity> {
public:
    template<typename U = T>
    void enqueue_begin(U&& value)
    {
        const auto new_head = (this->m_head - 1 + Capacity) % Capacity;
        auto& slot = this->elements()[new_head];
        if (this->m_size == Capacity)
            slot.~T();
        else
            ++this->m_size;

        new (&slot) T(forward<U>(value));
        this->m_head = new_head;
    }

    T dequeue_end()
    {
        VERIFY(!this->is_empty());
        auto& slot = this->elements()[(this->m_head + this->m_size - 1) % Capacity];
        T value = move(slot);
        slot.~T();
        this->m_size--;
        return value;
    }
};

}

using AK::CircularDeque;