sparse_set.hpp

#ifndef ENTT_ENTITY_SPARSE_SET_HPP
#define ENTT_ENTITY_SPARSE_SET_HPP
 
 
#include <algorithm>
#include <iterator>
#include <utility>
#include <vector>
#include <memory>
#include <cstddef>
#include <type_traits>
#include "../config/config.h"
#include "../core/algorithm.hpp"
#include "entity.hpp"
#include "fwd.hpp"
 
 
namespace entt {
 
 
template<typename Entity>
class sparse_set {
    using traits_type = entt_traits<std::underlying_type_t<Entity>>;
 
    static_assert(ENTT_PAGE_SIZE && ((ENTT_PAGE_SIZE & (ENTT_PAGE_SIZE - 1)) == 0));
    static constexpr auto entt_per_page = ENTT_PAGE_SIZE / sizeof(typename traits_type::entity_type);
 
    class iterator {
        friend class sparse_set<Entity>;
 
        using direct_type = std::vector<Entity>;
        using index_type = typename traits_type::difference_type;
 
        iterator(const direct_type *ref, const index_type idx) ENTT_NOEXCEPT
            : direct{ref}, index{idx}
        {}
 
    public:
        using difference_type = index_type;
        using value_type = Entity;
        using pointer = const value_type *;
        using reference = const value_type &;
        using iterator_category = std::random_access_iterator_tag;
 
        iterator() ENTT_NOEXCEPT = default;
 
        iterator & operator++() ENTT_NOEXCEPT {
            return --index, *this;
        }
 
        iterator operator++(int) ENTT_NOEXCEPT {
            iterator orig = *this;
            return operator++(), orig;
        }
 
        iterator & operator--() ENTT_NOEXCEPT {
            return ++index, *this;
        }
 
        iterator operator--(int) ENTT_NOEXCEPT {
            iterator orig = *this;
            return operator--(), orig;
        }
 
        iterator & operator+=(const difference_type value) ENTT_NOEXCEPT {
            index -= value;
            return *this;
        }
 
        iterator operator+(const difference_type value) const ENTT_NOEXCEPT {
            return iterator{direct, index-value};
        }
 
        iterator & operator-=(const difference_type value) ENTT_NOEXCEPT {
            return (*this += -value);
        }
 
        iterator operator-(const difference_type value) const ENTT_NOEXCEPT {
            return (*this + -value);
        }
 
        difference_type operator-(const iterator &other) const ENTT_NOEXCEPT {
            return other.index - index;
        }
 
        reference operator[](const difference_type value) const {
            const auto pos = size_type(index-value-1);
            return (*direct)[pos];
        }
 
        bool operator==(const iterator &other) const ENTT_NOEXCEPT {
            return other.index == index;
        }
 
        bool operator!=(const iterator &other) const ENTT_NOEXCEPT {
            return !(*this == other);
        }
 
        bool operator<(const iterator &other) const ENTT_NOEXCEPT {
            return index > other.index;
        }
 
        bool operator>(const iterator &other) const ENTT_NOEXCEPT {
            return index < other.index;
        }
 
        bool operator<=(const iterator &other) const ENTT_NOEXCEPT {
            return !(*this > other);
        }
 
        bool operator>=(const iterator &other) const ENTT_NOEXCEPT {
            return !(*this < other);
        }
 
        pointer operator->() const {
            const auto pos = size_type(index-1);
            return &(*direct)[pos];
        }
 
        reference operator*() const {
            return *operator->();
        }
 
    private:
        const direct_type *direct;
        index_type index;
    };
 
    auto page(const Entity entt) const ENTT_NOEXCEPT {
        return std::size_t{(to_integral(entt) & traits_type::entity_mask) / entt_per_page};
    }
 
    auto offset(const Entity entt) const ENTT_NOEXCEPT {
        return std::size_t{to_integral(entt) & (entt_per_page - 1)};
    }
 
    Entity * assure(const std::size_t pos) {
        if(!(pos < reverse.size())) {
            reverse.resize(pos+1);
        }
 
        if(!reverse[pos]) {
            reverse[pos] = std::make_unique<entity_type[]>(entt_per_page);
            // null is safe in all cases for our purposes
            std::fill_n(reverse[pos].get(), entt_per_page, null);
        }
 
        return reverse[pos].get();
    }
 
public:
    using entity_type = Entity;
    using size_type = std::size_t;
    using iterator_type = iterator;
 
    sparse_set() = default;
 
    sparse_set(sparse_set &&) = default;
 
    virtual ~sparse_set() = default;
 
    sparse_set & operator=(sparse_set &&) = default;
 
    void reserve(const size_type cap) {
        direct.reserve(cap);
    }
 
    size_type capacity() const ENTT_NOEXCEPT {
        return direct.capacity();
    }
 
    void shrink_to_fit() {
        // conservative approach
        if(direct.empty()) {
            reverse.clear();
        }
 
        reverse.shrink_to_fit();
        direct.shrink_to_fit();
    }
 
    size_type extent() const ENTT_NOEXCEPT {
        return reverse.size() * entt_per_page;
    }
 
    size_type size() const ENTT_NOEXCEPT {
        return direct.size();
    }
 
    bool empty() const ENTT_NOEXCEPT {
        return direct.empty();
    }
 
    const entity_type * data() const ENTT_NOEXCEPT {
        return direct.data();
    }
 
    iterator_type begin() const ENTT_NOEXCEPT {
        const typename traits_type::difference_type pos = direct.size();
        return iterator_type{&direct, pos};
    }
 
    iterator_type end() const ENTT_NOEXCEPT {
        return iterator_type{&direct, {}};
    }
 
    iterator_type find(const entity_type entt) const {
        return has(entt) ? --(end() - index(entt)) : end();
    }
 
    bool has(const entity_type entt) const {
        const auto curr = page(entt);
        // testing against null permits to avoid accessing the direct vector
        return (curr < reverse.size() && reverse[curr] && reverse[curr][offset(entt)] != null);
    }
 
    size_type index(const entity_type entt) const {
        ENTT_ASSERT(has(entt));
        return size_type(reverse[page(entt)][offset(entt)]);
    }
 
    void construct(const entity_type entt) {
        ENTT_ASSERT(!has(entt));
        assure(page(entt))[offset(entt)] = entity_type(direct.size());
        direct.push_back(entt);
    }
 
    template<typename It>
    void construct(It first, It last) {
        std::for_each(first, last, [this, next = direct.size()](const auto entt) mutable {
            ENTT_ASSERT(!has(entt));
            assure(page(entt))[offset(entt)] = entity_type(next++);
        });
 
        direct.insert(direct.end(), first, last);
    }
 
    void destroy(const entity_type entt) {
        ENTT_ASSERT(has(entt));
        const auto curr = page(entt);
        const auto pos = offset(entt);
        direct[size_type(reverse[curr][pos])] = entity_type(direct.back());
        reverse[page(direct.back())][offset(direct.back())] = reverse[curr][pos];
        reverse[curr][pos] = null;
        direct.pop_back();
    }
 
    virtual void swap(const entity_type lhs, const entity_type rhs) {
        auto &from = reverse[page(lhs)][offset(lhs)];
        auto &to = reverse[page(rhs)][offset(rhs)];
        std::swap(direct[size_type(from)], direct[size_type(to)]);
        std::swap(from, to);
    }
 
    template<typename Compare, typename Sort = std_sort, typename... Args>
    void sort(iterator_type first, iterator_type last, Compare compare, Sort algo = Sort{}, Args &&... args) {
        ENTT_ASSERT(!(last < first));
        ENTT_ASSERT(!(last > end()));
 
        const auto length = std::distance(first, last);
        const auto skip = std::distance(last, end());
        const auto to = direct.rend() - skip;
        const auto from = to - length;
 
        algo(from, to, std::move(compare), std::forward<Args>(args)...);
 
        for(size_type pos = skip, end = skip+length; pos < end; ++pos) {
            reverse[page(direct[pos])][offset(direct[pos])] = entity_type(pos);
        }
    }
 
    template<typename Apply, typename Compare, typename Sort = std_sort, typename... Args>
    void arrange(iterator_type first, iterator_type last, Apply apply, Compare compare, Sort algo = Sort{}, Args &&... args) {
        ENTT_ASSERT(!(last < first));
        ENTT_ASSERT(!(last > end()));
 
        const auto length = std::distance(first, last);
        const auto skip = std::distance(last, end());
        const auto to = direct.rend() - skip;
        const auto from = to - length;
 
        algo(from, to, std::move(compare), std::forward<Args>(args)...);
 
        for(size_type pos = skip, end = skip+length; pos < end; ++pos) {
            auto curr = pos;
            auto next = index(direct[curr]);
 
            while(curr != next) {
                apply(direct[curr], direct[next]);
                reverse[page(direct[curr])][offset(direct[curr])] = entity_type(curr);
 
                curr = next;
                next = index(direct[curr]);
            }
        }
    }
 
    void respect(const sparse_set &other) {
        const auto to = other.end();
        auto from = other.begin();
 
        size_type pos = direct.size() - 1;
 
        while(pos && from != to) {
            if(has(*from)) {
                if(*from != direct[pos]) {
                    swap(direct[pos], *from);
                }
 
                --pos;
            }
 
            ++from;
        }
    }
 
    void clear() ENTT_NOEXCEPT {
        reverse.clear();
        direct.clear();
    }
 
private:
    std::vector<std::unique_ptr<entity_type[]>> reverse;
    std::vector<entity_type> direct;
};
 
 
}
 
 
#endif