algorithm.hpp

#ifndef ENTT_CORE_ALGORITHM_HPP
#define ENTT_CORE_ALGORITHM_HPP
 
 
#include <vector>
#include <utility>
#include <iterator>
#include <algorithm>
#include <functional>
#include "utility.hpp"
 
 
namespace entt {
 
 
struct std_sort {
    template<typename It, typename Compare = std::less<>, typename... Args>
    void operator()(It first, It last, Compare compare = Compare{}, Args &&... args) const {
        std::sort(std::forward<Args>(args)..., std::move(first), std::move(last), std::move(compare));
    }
};
 
 
struct insertion_sort {
    template<typename It, typename Compare = std::less<>>
    void operator()(It first, It last, Compare compare = Compare{}) const {
        if(first < last) {
            for(auto it = first+1; it < last; ++it) {
                auto value = std::move(*it);
                auto pre = it;
 
                for(; pre > first && compare(value, *(pre-1)); --pre) {
                    *pre = std::move(*(pre-1));
                }
 
                *pre = std::move(value);
            }
        }
    }
};
 
 
template<std::size_t Bit, std::size_t N>
struct radix_sort {
    static_assert((N % Bit) == 0, "The maximum number of bits to sort must be a multiple of the number of bits processed per pass");
 
    template<typename It, typename Getter = identity>
    void operator()(It first, It last, Getter getter = Getter{}) const {
        if(first < last) {
            static constexpr auto mask = (1 << Bit) - 1;
            static constexpr auto buckets = 1 << Bit;
            static constexpr auto passes = N / Bit;
 
            using value_type = typename std::iterator_traits<It>::value_type;
            std::vector<value_type> aux(std::distance(first, last));
 
            auto part = [getter = std::move(getter)](auto from, auto to, auto out, auto start) {
                std::size_t index[buckets]{};
                std::size_t count[buckets]{};
 
                std::for_each(from, to, [&getter, &count, start](const value_type &item) {
                    ++count[(getter(item) >> start) & mask];
                });
 
                std::for_each(std::next(std::begin(index)), std::end(index), [index = std::begin(index), count = std::begin(count)](auto &item) mutable {
                    item = *(index++) + *(count++);
                });
 
                std::for_each(from, to, [&getter, &out, &index, start](value_type &item) {
                    out[index[(getter(item) >> start) & mask]++] = std::move(item);
                });
            };
 
            for(std::size_t pass = 0; pass < (passes & ~1); pass += 2) {
                part(first, last, aux.begin(), pass * Bit);
                part(aux.begin(), aux.end(), first, (pass + 1) * Bit);
            }
 
            if constexpr(passes & 1) {
                part(first, last, aux.begin(), (passes - 1) * Bit);
                std::move(aux.begin(), aux.end(), first);
            }
        }
    }
};
 
 
}
 
 
#endif