circular_queue.hh

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 * to a hardware implementation of the functionality of the software
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 * modified or unmodified, in source code or in binary form.
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#ifndef __BASE_CIRCULAR_QUEUE_HH__
#define __BASE_CIRCULAR_QUEUE_HH__
 
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <type_traits>
#include <vector>
 
namespace gem5
{
 
template <typename T>
class CircularQueue
{
  protected:
    std::vector<T> data;
 
    using reference = typename std::vector<T>::reference;
    using const_reference = typename std::vector<T>::const_reference;
    const size_t _capacity;
    size_t _size = 0;
    size_t _head = 1;
 
  public:
    struct iterator
    {
      public:
        CircularQueue* _cq = nullptr;
        size_t _idx = 0;
 
        iterator(CircularQueue* cq, size_t idx) : _cq(cq), _idx(idx) {}
        iterator() = default;
 
        using value_type = T;
        using difference_type = std::ptrdiff_t;
        using reference = value_type&;
        using const_reference = const value_type&;
        using pointer = value_type*;
        using const_pointer = const value_type*;
        using iterator_category = std::random_access_iterator_tag;
 // end of api_base_utils
 
        static_assert(std::is_same_v<reference, T&>,
                "reference type is not assignable as required");
 
        iterator(const iterator& it) : _cq(it._cq), _idx(it._idx) {}
 
        iterator&
        operator=(const iterator& it)
        {
            _cq = it._cq;
            _idx = it._idx;
            return *this;
        }
 
        bool
        dereferenceable() const
        {
            return _cq != nullptr && _cq->isValidIdx(_idx);
        }
 
        bool
        operator==(const iterator& that) const
        {
            return _cq == that._cq && _idx == that._idx;
        }
 
        bool operator!=(const iterator& that) { return !(*this == that); }
 
        reference
        operator*()
        {
            // This has to be dereferenceable.
            return (*_cq)[_idx];
        }
 
        const_reference
        operator*() const
        {
            // This has to be dereferenceable.
            return (*_cq)[_idx];
        }
 
        pointer operator->() { return &**this; }
 
        const_pointer operator->() const { return &**this; }
 
        iterator&
        operator++()
        {
            ++_idx;
            return *this;
        }
 
        iterator
        operator++(int)
        {
            iterator t = *this;
            ++*this;
            return t;
        }
 
      public:
        iterator&
        operator--()
        {
            /* this has to be decrementable. */
            assert(_cq && _idx > _cq->head());
            --_idx;
            return *this;
        }
 
        iterator
        operator--(int)
        {
            iterator t = *this;
            --*this;
            return t;
        }
 
        iterator&
        operator+=(const difference_type& t)
        {
            _idx += t;
            return *this;
        }
 
        iterator&
        operator-=(const difference_type& t)
        {
            assert(_cq && _idx >= _cq->head() + t);
            _idx -= t;
            return *this;
        }
 
        iterator
        operator+(const difference_type& t)
        {
            iterator ret(*this);
            return ret += t;
        }
 
        friend iterator
        operator+(const difference_type& t, iterator& it)
        {
            iterator ret = it;
            return ret += t;
        }
 
        iterator
        operator-(const difference_type& t)
        {
            iterator ret(*this);
            return ret -= t;
        }
 
        friend iterator
        operator-(const difference_type& t, iterator& it)
        {
            iterator ret = it;
            return ret -= t;
        }
 
        difference_type
        operator-(const iterator& that)
        {
            return (ssize_t)_idx - (ssize_t)that._idx;
        }
 
        template<typename Idx>
        typename std::enable_if_t<std::is_integral_v<Idx>, reference>
        operator[](const Idx& index)
        {
            return *(*this + index);
        }
 
        bool
        operator<(const iterator& that) const
        {
            return _idx < that._idx;
        }
 
        bool operator>(const iterator& that) const { return !(*this <= that); }
 
        bool operator>=(const iterator& that) const { return !(*this < that); }
 
        bool operator<=(const iterator& that) const { return !(that < *this); }
 
        size_t idx() const { return _idx; }
    };
 
  public:
    template <typename Idx>
    typename std::enable_if_t<std::is_integral_v<Idx>, reference>
    operator[](const Idx& index)
    {
        assert(index >= 0);
        return data[index % _capacity];
    }
 
    template <typename Idx>
    typename std::enable_if_t<std::is_integral_v<Idx>, const_reference>
    operator[](const Idx& index) const
    {
        assert(index >= 0);
        return data[index % _capacity];
    }
 
    explicit CircularQueue(size_t size=0) : data(size), _capacity(size) {}
 
    void
    flush()
    {
        _head = 1;
        _size = 0;
    }
 
    bool
    isValidIdx(size_t idx) const
    {
        return _head <= idx && idx < (_head + _size);
    }
 
    reference front() { return (*this)[head()]; }
 
    reference back() { return (*this)[tail()]; }
 
    size_t head() const { return _head; }
 
    size_t tail() const { return _head + _size - 1; }
 
    size_t capacity() const { return _capacity; }
 
    size_t size() const { return _size; }
 
    void
    pop_front(size_t num_elem=1)
    {
        assert(num_elem <= size());
        _head += num_elem;
        _size -= num_elem;
    }
 
    void
    pop_back()
    {
        assert(!empty());
        --_size;
    }
 
    void
    push_back(typename std::vector<T>::value_type val)
    {
        advance_tail();
        back() = val;
    }
 
    void
    advance_tail()
    {
        if (full())
            ++_head;
        else
            ++_size;
    }
 
    void
    advance_tail(size_t len)
    {
        size_t remaining = _capacity - _size;
        if (len > remaining) {
            size_t overflow = len - remaining;
            _head += overflow;
            len -= overflow;
        }
        _size += len;
    }
 
    bool empty() const { return _size == 0; }
 
    bool full() const { return _size == _capacity; }
 
    iterator begin() { return iterator(this, _head); }
 
    /* TODO: This should return a const_iterator. */
    iterator
    begin() const
    {
        return iterator(const_cast<CircularQueue*>(this), _head);
    }
 
    iterator end() { return iterator(this, tail() + 1); }
 
    iterator
    end() const
    {
        return iterator(const_cast<CircularQueue*>(this), tail() + 1);
    }
 
    iterator getIterator(size_t idx) { return iterator(this, idx); }
};
 
} // namespace gem5
 
#endif /* __BASE_CIRCULARQUEUE_HH__ */