prevector.h

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// Copyright (c) 2015-2016 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
#ifndef BITCOIN_PREVECTOR_H
#define BITCOIN_PREVECTOR_H
 
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <type_traits>
#include <utility>
 
template <unsigned int N, typename T, typename Size = uint32_t,
          typename Diff = int32_t>
class prevector {
    static_assert(std::is_trivially_copyable_v<T>);
 
public:
    static constexpr unsigned int STATIC_SIZE{N};
 
    typedef Size size_type;
    typedef Diff difference_type;
    typedef T value_type;
    typedef value_type &reference;
    typedef const value_type &const_reference;
    typedef value_type *pointer;
    typedef const value_type *const_pointer;
 
    class iterator {
        T *ptr;
 
    public:
        typedef Diff difference_type;
        typedef T value_type;
        typedef T *pointer;
        typedef T &reference;
        typedef std::random_access_iterator_tag iterator_category;
        iterator() : ptr(nullptr) {}
        iterator(T *ptr_) : ptr(ptr_) {}
        T &operator*() const { return *ptr; }
        T *operator->() const { return ptr; }
        T &operator[](size_type pos) { return ptr[pos]; }
        const T &operator[](size_type pos) const { return ptr[pos]; }
        iterator &operator++() {
            ptr++;
            return *this;
        }
        iterator &operator--() {
            ptr--;
            return *this;
        }
        iterator operator++(int) {
            iterator copy(*this);
            ++(*this);
            return copy;
        }
        iterator operator--(int) {
            iterator copy(*this);
            --(*this);
            return copy;
        }
        difference_type friend operator-(iterator a, iterator b) {
            return (&(*a) - &(*b));
        }
        iterator operator+(size_type n) { return iterator(ptr + n); }
        iterator &operator+=(size_type n) {
            ptr += n;
            return *this;
        }
        iterator operator-(size_type n) { return iterator(ptr - n); }
        iterator &operator-=(size_type n) {
            ptr -= n;
            return *this;
        }
        bool operator==(iterator x) const { return ptr == x.ptr; }
        bool operator!=(iterator x) const { return ptr != x.ptr; }
        bool operator>=(iterator x) const { return ptr >= x.ptr; }
        bool operator<=(iterator x) const { return ptr <= x.ptr; }
        bool operator>(iterator x) const { return ptr > x.ptr; }
        bool operator<(iterator x) const { return ptr < x.ptr; }
    };
 
    class reverse_iterator {
        T *ptr;
 
    public:
        typedef Diff difference_type;
        typedef T value_type;
        typedef T *pointer;
        typedef T &reference;
        typedef std::bidirectional_iterator_tag iterator_category;
        reverse_iterator() : ptr(nullptr) {}
        reverse_iterator(T *ptr_) : ptr(ptr_) {}
        T &operator*() { return *ptr; }
        const T &operator*() const { return *ptr; }
        T *operator->() { return ptr; }
        const T *operator->() const { return ptr; }
        reverse_iterator &operator--() {
            ptr++;
            return *this;
        }
        reverse_iterator &operator++() {
            ptr--;
            return *this;
        }
        reverse_iterator operator++(int) {
            reverse_iterator copy(*this);
            ++(*this);
            return copy;
        }
        reverse_iterator operator--(int) {
            reverse_iterator copy(*this);
            --(*this);
            return copy;
        }
        bool operator==(reverse_iterator x) const { return ptr == x.ptr; }
        bool operator!=(reverse_iterator x) const { return ptr != x.ptr; }
    };
 
    class const_iterator {
        const T *ptr;
 
    public:
        typedef Diff difference_type;
        typedef const T value_type;
        typedef const T *pointer;
        typedef const T &reference;
        typedef std::random_access_iterator_tag iterator_category;
        const_iterator() : ptr(nullptr) {}
        const_iterator(const T *ptr_) : ptr(ptr_) {}
        const_iterator(iterator x) : ptr(&(*x)) {}
        const T &operator*() const { return *ptr; }
        const T *operator->() const { return ptr; }
        const T &operator[](size_type pos) const { return ptr[pos]; }
        const_iterator &operator++() {
            ptr++;
            return *this;
        }
        const_iterator &operator--() {
            ptr--;
            return *this;
        }
        const_iterator operator++(int) {
            const_iterator copy(*this);
            ++(*this);
            return copy;
        }
        const_iterator operator--(int) {
            const_iterator copy(*this);
            --(*this);
            return copy;
        }
        difference_type friend operator-(const_iterator a, const_iterator b) {
            return (&(*a) - &(*b));
        }
        const_iterator operator+(size_type n) {
            return const_iterator(ptr + n);
        }
        const_iterator &operator+=(size_type n) {
            ptr += n;
            return *this;
        }
        const_iterator operator-(size_type n) {
            return const_iterator(ptr - n);
        }
        const_iterator &operator-=(size_type n) {
            ptr -= n;
            return *this;
        }
        bool operator==(const_iterator x) const { return ptr == x.ptr; }
        bool operator!=(const_iterator x) const { return ptr != x.ptr; }
        bool operator>=(const_iterator x) const { return ptr >= x.ptr; }
        bool operator<=(const_iterator x) const { return ptr <= x.ptr; }
        bool operator>(const_iterator x) const { return ptr > x.ptr; }
        bool operator<(const_iterator x) const { return ptr < x.ptr; }
    };
 
    class const_reverse_iterator {
        const T *ptr;
 
    public:
        typedef Diff difference_type;
        typedef const T value_type;
        typedef const T *pointer;
        typedef const T &reference;
        typedef std::bidirectional_iterator_tag iterator_category;
        const_reverse_iterator() : ptr(nullptr) {}
        const_reverse_iterator(const T *ptr_) : ptr(ptr_) {}
        const_reverse_iterator(reverse_iterator x) : ptr(&(*x)) {}
        const T &operator*() const { return *ptr; }
        const T *operator->() const { return ptr; }
        const_reverse_iterator &operator--() {
            ptr++;
            return *this;
        }
        const_reverse_iterator &operator++() {
            ptr--;
            return *this;
        }
        const_reverse_iterator operator++(int) {
            const_reverse_iterator copy(*this);
            ++(*this);
            return copy;
        }
        const_reverse_iterator operator--(int) {
            const_reverse_iterator copy(*this);
            --(*this);
            return copy;
        }
        bool operator==(const_reverse_iterator x) const { return ptr == x.ptr; }
        bool operator!=(const_reverse_iterator x) const { return ptr != x.ptr; }
    };
 
private:
#pragma pack(push, 1)
    union direct_or_indirect {
        char direct[sizeof(T) * N];
        struct {
            char *indirect;
            size_type capacity;
        } indirect_contents;
    };
#pragma pack(pop)
    alignas(char *) direct_or_indirect _union = {};
    size_type _size = 0;
 
    static_assert(alignof(char *) % alignof(size_type) == 0 &&
                      sizeof(char *) % alignof(size_type) == 0,
                  "size_type cannot have more restrictive alignment "
                  "requirement than pointer");
    static_assert(alignof(char *) % alignof(T) == 0,
                  "value_type T cannot have more restrictive alignment "
                  "requirement than pointer");
 
    T *direct_ptr(difference_type pos) {
        return reinterpret_cast<T *>(_union.direct) + pos;
    }
    const T *direct_ptr(difference_type pos) const {
        return reinterpret_cast<const T *>(_union.direct) + pos;
    }
    T *indirect_ptr(difference_type pos) {
        return reinterpret_cast<T *>(_union.indirect_contents.indirect) + pos;
    }
    const T *indirect_ptr(difference_type pos) const {
        return reinterpret_cast<const T *>(_union.indirect_contents.indirect) +
               pos;
    }
    bool is_direct() const { return _size <= N; }
 
    void change_capacity(size_type new_capacity) {
        if (new_capacity <= N) {
            if (!is_direct()) {
                T *indirect = indirect_ptr(0);
                T *src = indirect;
                T *dst = direct_ptr(0);
                memcpy(dst, src, size() * sizeof(T));
                free(indirect);
                _size -= N + 1;
            }
        } else {
            if (!is_direct()) {
                // FIXME: Because malloc/realloc here won't call new_handler if
                // allocation fails, assert success. These should instead use an
                // allocator or new/delete so that handlers are called as
                // necessary, but performance would be slightly degraded by
                // doing so.
                _union.indirect_contents.indirect = static_cast<char *>(
                    realloc(_union.indirect_contents.indirect,
                            ((size_t)sizeof(T)) * new_capacity));
                assert(_union.indirect_contents.indirect);
                _union.indirect_contents.capacity = new_capacity;
            } else {
                char *new_indirect = static_cast<char *>(
                    malloc(((size_t)sizeof(T)) * new_capacity));
                assert(new_indirect);
                T *src = direct_ptr(0);
                T *dst = reinterpret_cast<T *>(new_indirect);
                memcpy(dst, src, size() * sizeof(T));
                _union.indirect_contents.indirect = new_indirect;
                _union.indirect_contents.capacity = new_capacity;
                _size += N + 1;
            }
        }
    }
 
    T *item_ptr(difference_type pos) {
        return is_direct() ? direct_ptr(pos) : indirect_ptr(pos);
    }
    const T *item_ptr(difference_type pos) const {
        return is_direct() ? direct_ptr(pos) : indirect_ptr(pos);
    }
 
    void fill(T *dst, ptrdiff_t count, const T &value = T{}) {
        std::fill_n(dst, count, value);
    }
 
    template <typename InputIterator>
    void fill(T *dst, InputIterator first, InputIterator last) {
        while (first != last) {
            new (static_cast<void *>(dst)) T(*first);
            ++dst;
            ++first;
        }
    }
 
public:
    void assign(size_type n, const T &val) {
        clear();
        if (capacity() < n) {
            change_capacity(n);
        }
        _size += n;
        fill(item_ptr(0), n, val);
    }
 
    template <typename InputIterator>
    void assign(InputIterator first, InputIterator last) {
        size_type n = last - first;
        clear();
        if (capacity() < n) {
            change_capacity(n);
        }
        _size += n;
        fill(item_ptr(0), first, last);
    }
 
    prevector() {}
 
    explicit prevector(size_type n) { resize(n); }
 
    explicit prevector(size_type n, const T &val) {
        change_capacity(n);
        _size += n;
        fill(item_ptr(0), n, val);
    }
 
    template <typename InputIterator>
    prevector(InputIterator first, InputIterator last) {
        size_type n = last - first;
        change_capacity(n);
        _size += n;
        fill(item_ptr(0), first, last);
    }
 
    prevector(const prevector<N, T, Size, Diff> &other) {
        size_type n = other.size();
        change_capacity(n);
        _size += n;
        fill(item_ptr(0), other.begin(), other.end());
    }
 
    prevector(prevector<N, T, Size, Diff> &&other) noexcept
        : _union(std::move(other._union)), _size(other._size) {
        other._size = 0;
    }
 
    prevector &operator=(const prevector<N, T, Size, Diff> &other) {
        if (&other == this) {
            return *this;
        }
        assign(other.begin(), other.end());
        return *this;
    }
 
    prevector &operator=(prevector<N, T, Size, Diff> &&other) noexcept {
        if (!is_direct()) {
            free(_union.indirect_contents.indirect);
        }
        _union = std::move(other._union);
        _size = other._size;
        other._size = 0;
        return *this;
    }
 
    size_type size() const { return is_direct() ? _size : _size - N - 1; }
 
    bool empty() const { return size() == 0; }
 
    iterator begin() { return iterator(item_ptr(0)); }
    const_iterator begin() const { return const_iterator(item_ptr(0)); }
    iterator end() { return iterator(item_ptr(size())); }
    const_iterator end() const { return const_iterator(item_ptr(size())); }
 
    reverse_iterator rbegin() { return reverse_iterator(item_ptr(size() - 1)); }
    const_reverse_iterator rbegin() const {
        return const_reverse_iterator(item_ptr(size() - 1));
    }
    reverse_iterator rend() { return reverse_iterator(item_ptr(-1)); }
    const_reverse_iterator rend() const {
        return const_reverse_iterator(item_ptr(-1));
    }
 
    size_t capacity() const {
        if (is_direct()) {
            return N;
        } else {
            return _union.indirect_contents.capacity;
        }
    }
 
    T &operator[](size_type pos) { return *item_ptr(pos); }
 
    const T &operator[](size_type pos) const { return *item_ptr(pos); }
 
    void resize(size_type new_size) {
        size_type cur_size = size();
        if (cur_size == new_size) {
            return;
        }
        if (cur_size > new_size) {
            erase(item_ptr(new_size), end());
            return;
        }
        if (new_size > capacity()) {
            change_capacity(new_size);
        }
        ptrdiff_t increase = new_size - cur_size;
        fill(item_ptr(cur_size), increase);
        _size += increase;
    }
 
    void reserve(size_type new_capacity) {
        if (new_capacity > capacity()) {
            change_capacity(new_capacity);
        }
    }
 
    void shrink_to_fit() { change_capacity(size()); }
 
    void clear() { resize(0); }
 
    iterator insert(iterator pos, const T &value) {
        size_type p = pos - begin();
        size_type new_size = size() + 1;
        if (capacity() < new_size) {
            change_capacity(new_size + (new_size >> 1));
        }
        T *ptr = item_ptr(p);
        memmove(ptr + 1, ptr, (size() - p) * sizeof(T));
        _size++;
        new (static_cast<void *>(ptr)) T(value);
        return iterator(ptr);
    }
 
    void insert(iterator pos, size_type count, const T &value) {
        size_type p = pos - begin();
        size_type new_size = size() + count;
        if (capacity() < new_size) {
            change_capacity(new_size + (new_size >> 1));
        }
        T *ptr = item_ptr(p);
        memmove(ptr + count, ptr, (size() - p) * sizeof(T));
        _size += count;
        fill(item_ptr(p), count, value);
    }
 
    template <typename InputIterator>
    void insert(iterator pos, InputIterator first, InputIterator last) {
        size_type p = pos - begin();
        difference_type count = last - first;
        size_type new_size = size() + count;
        if (capacity() < new_size) {
            change_capacity(new_size + (new_size >> 1));
        }
        T *ptr = item_ptr(p);
        memmove(ptr + count, ptr, (size() - p) * sizeof(T));
        _size += count;
        fill(ptr, first, last);
    }
 
    inline void resize_uninitialized(size_type new_size) {
        // resize_uninitialized changes the size of the prevector but does not
        // initialize it. If size < new_size, the added elements must be
        // initialized explicitly.
        if (capacity() < new_size) {
            change_capacity(new_size);
            _size += new_size - size();
            return;
        }
        if (new_size < size()) {
            erase(item_ptr(new_size), end());
        } else {
            _size += new_size - size();
        }
    }
 
    iterator erase(iterator pos) { return erase(pos, pos + 1); }
 
    iterator erase(iterator first, iterator last) {
        // Erase is not allowed to the change the object's capacity. That means
        // that when starting with an indirectly allocated prevector with
        // size and capacity > N, the result may be a still indirectly allocated
        // prevector with size <= N and capacity > N. A shrink_to_fit() call is
        // necessary to switch to the (more efficient) directly allocated
        // representation (with capacity N and size <= N).
        iterator p = first;
        char *endp = (char *)&(*end());
        _size -= last - p;
        memmove(&(*first), &(*last), endp - ((char *)(&(*last))));
        return first;
    }
 
    template <typename... Args> void emplace_back(Args &&...args) {
        size_type new_size = size() + 1;
        if (capacity() < new_size) {
            change_capacity(new_size + (new_size >> 1));
        }
        new (item_ptr(size())) T(std::forward<Args>(args)...);
        _size++;
    }
 
    void push_back(const T &value) { emplace_back(value); }
 
    void pop_back() { erase(end() - 1, end()); }
 
    T &front() { return *item_ptr(0); }
 
    const T &front() const { return *item_ptr(0); }
 
    T &back() { return *item_ptr(size() - 1); }
 
    const T &back() const { return *item_ptr(size() - 1); }
 
    void swap(prevector<N, T, Size, Diff> &other) noexcept {
        std::swap(_union, other._union);
        std::swap(_size, other._size);
    }
 
    ~prevector() {
        if (!is_direct()) {
            free(_union.indirect_contents.indirect);
            _union.indirect_contents.indirect = nullptr;
        }
    }
 
    bool operator==(const prevector<N, T, Size, Diff> &other) const {
        if (other.size() != size()) {
            return false;
        }
        const_iterator b1 = begin();
        const_iterator b2 = other.begin();
        const_iterator e1 = end();
        while (b1 != e1) {
            if ((*b1) != (*b2)) {
                return false;
            }
            ++b1;
            ++b2;
        }
        return true;
    }
 
    bool operator!=(const prevector<N, T, Size, Diff> &other) const {
        return !(*this == other);
    }
 
    bool operator<(const prevector<N, T, Size, Diff> &other) const {
        if (size() < other.size()) {
            return true;
        }
        if (size() > other.size()) {
            return false;
        }
        const_iterator b1 = begin();
        const_iterator b2 = other.begin();
        const_iterator e1 = end();
        while (b1 != e1) {
            if ((*b1) < (*b2)) {
                return true;
            }
            if ((*b2) < (*b1)) {
                return false;
            }
            ++b1;
            ++b2;
        }
        return false;
    }
 
    size_t allocated_memory() const {
        if (is_direct()) {
            return 0;
        } else {
            return ((size_t)(sizeof(T))) * _union.indirect_contents.capacity;
        }
    }
 
    value_type *data() { return item_ptr(0); }
 
    const value_type *data() const { return item_ptr(0); }
};
 
#endif // BITCOIN_PREVECTOR_H