bit_sort.hpp

/*********************************************************************
 *
 *  Linear Arrangement Library - A library that implements a collection
 *  algorithms for linear arrangments of graphs.
 *
 *  Copyright (C) 2019 - 2021
 *
 *  This file is part of Linear Arrangement Library. To see the full code
 *  visit the webpage:
 *      https://github.com/lluisalemanypuig/linear-arrangement-library.git
 *
 *  Linear Arrangement Library is free software: you can redistribute it
 *  and/or modify it under the terms of the GNU Affero General Public License
 *  as published by the Free Software Foundation, either version 3 of the
 *  License, or (at your option) any later version.
 *
 *  Linear Arrangement Library is distributed in the hope that it will be
 *  useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *  GNU Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with Linear Arrangement Library.  If not, see <http://www.gnu.org/licenses/>.
 *
 *  Contact:
 *
 *      Lluís Alemany Puig (lalemany@cs.upc.edu)
 *          LARCA (Laboratory for Relational Algorithmics, Complexity and Learning)
 *          CQL (Complexity and Quantitative Linguistics Lab)
 *          Jordi Girona St 1-3, Campus Nord UPC, 08034 Barcelona.   CATALONIA, SPAIN
 *          Webpage: https://cqllab.upc.edu/people/lalemany/
 *
 *      Ramon Ferrer i Cancho (rferrericancho@cs.upc.edu)
 *          LARCA (Laboratory for Relational Algorithmics, Complexity and Learning)
 *          CQL (Complexity and Quantitative Linguistics Lab)
 *          Office S124, Omega building
 *          Jordi Girona St 1-3, Campus Nord UPC, 08034 Barcelona.   CATALONIA, SPAIN
 *          Webpage: https://cqllab.upc.edu/people/rferrericancho/
 *
 ********************************************************************/
 
#pragma once
 
// C++ includes
#include <algorithm>
 
// lal includes
#include <lal/internal/data_array.hpp>
#include <lal/internal/sorting/insertion_sort.hpp>
#include <lal/internal/macros.hpp>
 
namespace lal {
namespace internal {
 
namespace __lal {
 
/*
 * @brief Sorts the elements within range [begin, end)
 *
 * @param begin Iterator at the beginning of the container.
 * @param end Iterator at the end of the container.
 * @param seen The bit array used to sort.
 * @pre All values of @e mem must be set to false.
 * @pre All values within [begin, end) must be unique.
 * @post All the values of @e seen are set to false.
 * @post The elements in the range [begin,end) are sorted increasingly.
 */
template<
    typename T, typename It,
    std::enable_if_t<
        std::is_integral_v<T> && is_pointer_iterator_v<T, It>,
        bool
    > = true
>
void __bit_sort(It begin, It end, const T& m, char * const seen) {
    // fill bit array
    for (auto it = begin; it != end; ++it) {
        seen[*it - m] = 1;
    }
 
    // pointer to see
    size_t seenit = 0;
    // element to assign to container
    T i = m;
 
    // pointer to container
    It it = begin;
    while (it != end) {
        // assign value to container
        *it = i;
        it += seen[seenit];
 
        // move pointer in bit array
        seen[seenit] = 0;
        ++i;
        ++seenit;
    }
}
 
} // -- namespace __lal
 
/*
 * @brief Sort integer values increasingly.
 *
 * @param begin Iterator at the beginning of the container.
 * @param end Iterator at the end of the container.
 * @param size The value of std::distance(begin, end), i.e., the number of
 * elements from begin to sort, i.e., the size of the container.
 * @param seen The bit array used to sort.
 * @pre All values of @e mem must be set to 0.
 * @pre All values within [begin, end) must be unique.
 * @post All the values of @e seen are set to 0.
 * @post The elements in the range [begin,end) are sorted increasingly.
 */
template<
    typename T, typename It,
    std::enable_if_t<
        std::is_integral_v<T> && is_pointer_iterator_v<T, It>,
        bool
    > = true
>
void bit_sort_mem(It begin, It end, const size_t size, char * const seen)
{
    if (size <= 1) { return; }
    if (size <= 14) {
        insertion_sort(begin, end);
        return;
    }
    if (size <= 30) {
        std::sort(begin, end);
        return;
    }
 
    // sort
    __lal::__bit_sort(begin,end, static_cast<T>(0), seen);
}
 
/*
 * @brief Sort integer values increasingly.
 *
 * @param begin Iterator at the beginning of the container.
 * @param end Iterator at the end of the container.
 * @param size The value of std::distance(begin, end), i.e., the number of
 * elements from begin to sort, i.e., the size of the container.
 * @pre All values within [begin, end) must be unique.
 * @post The elements in the range [begin,end) are sorted increasingly.
 */
template<
    typename T, typename It,
    std::enable_if_t<
        std::is_integral_v<T> && is_pointer_iterator_v<T, It>,
        bool
    > = true
>
void bit_sort(It begin, It end, const size_t size)
{
    if (size <= 1) { return; }
    if (size <= 14) {
        insertion_sort(begin, end);
        return;
    }
    if (size <= 30) {
        std::sort(begin, end);
        return;
    }
 
    // maximum & minimum elements within array
    const auto [m_it,M_it] = std::minmax_element(begin, end);
    const auto m = *m_it;
    const auto M = *M_it;
 
    // bit array
    data_array<char> seen(M - m + 1, 0);
 
    // sort
    __lal::__bit_sort(begin,end, m, seen.data);
}
 
} // -- namspace utils
} // -- namespace lal