bit_sort.hpp

/*********************************************************************
 *
 * Linear Arrangement Library - A library that implements a collection
 * algorithms for linear arrangments of graphs.
 *
 * Copyright (C) 2019 - 2024
 *
 * This file is part of Linear Arrangement Library. The full code is available
 * at:
 *      https://github.com/LAL-project/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 (lluis.alemany.puig@upc.edu)
 *         LQMC (Quantitative, Mathematical, and Computational Linguisitcs)
 *         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)
 *         LQMC (Quantitative, Mathematical, and Computational Linguisitcs)
 *         CQL (Complexity and Quantitative Linguistics Lab)
 *         Office 220, 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/detail/array.hpp>
#include <lal/detail/sorting/insertion_sort.hpp>
#include <lal/detail/type_traits/is_pointer_iterator.hpp>
 
namespace lal {
namespace detail {
namespace sorting {
 
template <
    typename T, typename iterator_t,
    std::enable_if_t<
        std::is_integral_v<T> and is_pointer_iterator_v<T, iterator_t>,
        bool
    > = true
>
void bit_sort
(
    const iterator_t begin,
    const iterator_t end,
    const T& m,
    char * const seen
)
noexcept
{
    // fill bit array
    for (auto it = begin; it != end; ++it) {
        seen[*it - m] = 1;
    }
 
    // pointer to see
    std::size_t seenit = 0;
    // element to assign to container
    T i = m;
 
    // pointer to container
    iterator_t it = begin;
    while (it != end) {
        // assign value to container
        *it = i;
        it += seen[seenit];
 
        // move pointer in bit array
        seen[seenit] = 0;
        ++i;
        ++seenit;
    }
}
 
template <
    typename T, typename It,
    std::enable_if_t<
        std::is_integral_v<T> and is_pointer_iterator_v<T, It>,
        bool
    > = true
>
void bit_sort_mem
(
    const It begin,
    const It end,
    const std::size_t size,
    char * const seen
)
noexcept
{
    if (size <= 1) { return; }
    if (size <= 14) {
        insertion_sort(begin, end);
        return;
    }
    if (size <= 30) {
        std::sort(begin, end);
        return;
    }
 
    bit_sort(begin,end, T{0}, seen);
}
 
template <
    typename T, typename It,
    std::enable_if_t<
        std::is_integral_v<T> and is_pointer_iterator_v<T, It>,
        bool
    > = true
>
void bit_sort
(
    const It begin,
    const It end,
    const std::size_t size
)
noexcept
{
    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
    array<char> seen(M - m + 1, 0);
 
    bit_sort(begin,end, m, seen.begin());
}
 
} // -- namespace sorting
} // -- namspace utils
} // -- namespace lal