parallel/container_algorithms/minmax.hpp

//  Copyright (c) 2014-2016 Hartmut Kaiser
//
//  Distributed under the Boost Software License, Version 1.0. (See accompanying
//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

// make inspect happy: hpxinspect:nominmax

/// \file parallel/container_algorithms/minmax.hpp

#if !defined(HPX_PARALLEL_CONTAINER_ALGORITHMS_MINMAX_JAN_25_2016_1218PM)
#define HPX_PARALLEL_CONTAINER_ALGORITHMS_MINMAX_JAN_25_2016_1218PM

#include <hpx/config.hpp>
#include <hpx/traits/concepts.hpp>
#include <hpx/traits/is_range.hpp>
#include <hpx/util/range.hpp>
#include <hpx/util/tagged_pair.hpp>

#include <hpx/parallel/algorithms/minmax.hpp>
#include <hpx/parallel/traits/projected.hpp>
#include <hpx/parallel/traits/projected_range.hpp>

#include <type_traits>
#include <utility>

namespace hpx { namespace parallel { inline namespace v1
{
    /// Finds the smallest element in the range [first, last) using the given
    /// comparison function \a f.
    ///
    /// \note   Complexity: Exactly \a max(N-1, 0) comparisons, where
    ///                     N = std::distance(first, last).
    ///
    /// \tparam ExPolicy    The type of the execution policy to use (deduced).
    ///                     It describes the manner in which the execution
    ///                     of the algorithm may be parallelized and the manner
    ///                     in which it executes the assignments.
    /// \tparam Rng         The type of the source range used (deduced).
    ///                     The iterators extracted from this range type must
    ///                     meet the requirements of an forward iterator.
    /// \tparam F           The type of the function/function object to use
    ///                     (deduced). Unlike its sequential form, the parallel
    ///                     overload of \a min_element requires \a F to meet the
    ///                     requirements of \a CopyConstructible.
    /// \tparam Proj        The type of an optional projection function. This
    ///                     defaults to \a util::projection_identity
    ///
    /// \param policy       The execution policy to use for the scheduling of
    ///                     the iterations.
    /// \param rng          Refers to the sequence of elements the algorithm
    ///                     will be applied to.
    /// \param f            The binary predicate which returns true if the
    ///                     the left argument is less than the right element.
    ///                     The signature
    ///                     of the predicate function should be equivalent to
    ///                     the following:
    ///                     \code
    ///                     bool pred(const Type1 &a, const Type1 &b);
    ///                     \endcode \n
    ///                     The signature does not need to have const &, but
    ///                     the function must not modify the objects passed to
    ///                     it. The type \a Type1 must be such that objects of
    ///                     type \a FwdIter can be dereferenced and then
    ///                     implicitly converted to \a Type1.
    /// \param proj         Specifies the function (or function object) which
    ///                     will be invoked for each of the elements as a
    ///                     projection operation before the actual predicate
    ///                     \a is invoked.
    ///
    /// The comparisons in the parallel \a min_element algorithm invoked with
    /// an execution policy object of type \a sequenced_policy
    /// execute in sequential order in the calling thread.
    ///
    /// The comparisons in the parallel \a min_element algorithm invoked with
    /// an execution policy object of type \a parallel_policy or
    /// \a parallel_task_policy are permitted to execute in an unordered
    /// fashion in unspecified threads, and indeterminately sequenced
    /// within each thread.
    ///
    /// \returns  The \a min_element algorithm returns a \a hpx::future<FwdIter>
    ///           if the execution policy is of type
    ///           \a sequenced_task_policy or
    ///           \a parallel_task_policy
    ///           and returns \a FwdIter otherwise.
    ///           The \a min_element algorithm returns the iterator to the
    ///           smallest element in the range [first, last). If several
    ///           elements in the range are equivalent to the smallest element,
    ///           returns the iterator to the first such element. Returns last
    ///           if the range is empty.
    ///
    template <typename ExPolicy, typename Rng,
        typename Proj = util::projection_identity,
        typename F = detail::less,
    HPX_CONCEPT_REQUIRES_(
        execution::is_execution_policy<ExPolicy>::value &&
        hpx::traits::is_range<Rng>::value &&
        traits::is_projected_range<Proj, Rng>::value &&
        traits::is_indirect_callable<
            ExPolicy, F,
                traits::projected_range<Proj, Rng>,
                traits::projected_range<Proj, Rng>
        >::value)>
    typename util::detail::algorithm_result<
        ExPolicy, typename hpx::traits::range_traits<Rng>::iterator_type
    >::type
    min_element(ExPolicy && policy, Rng && rng, F && f = F(),
        Proj && proj = Proj())
    {
        return min_element(std::forward<ExPolicy>(policy),
            hpx::util::begin(rng), hpx::util::end(rng),
            std::forward<F>(f), std::forward<Proj>(proj));
    }

    /// Finds the greatest element in the range [first, last) using the given
    /// comparison function \a f.
    ///
    /// \note   Complexity: Exactly \a max(N-1, 0) comparisons, where
    ///                     N = std::distance(first, last).
    ///
    /// \tparam ExPolicy    The type of the execution policy to use (deduced).
    ///                     It describes the manner in which the execution
    ///                     of the algorithm may be parallelized and the manner
    ///                     in which it executes the assignments.
    /// \tparam Rng         The type of the source range used (deduced).
    ///                     The iterators extracted from this range type must
    ///                     meet the requirements of an forward iterator.
    /// \tparam F           The type of the function/function object to use
    ///                     (deduced). Unlike its sequential form, the parallel
    ///                     overload of \a max_element requires \a F to meet the
    ///                     requirements of \a CopyConstructible.
    /// \tparam Proj        The type of an optional projection function. This
    ///                     defaults to \a util::projection_identity
    ///
    /// \param policy       The execution policy to use for the scheduling of
    ///                     the iterations.
    /// \param rng          Refers to the sequence of elements the algorithm
    ///                     will be applied to.
    /// \param f            The binary predicate which returns true if the
    ///                     This argument is optional and defaults to std::less.
    ///                     the left argument is less than the right element.
    ///                     The signature
    ///                     of the predicate function should be equivalent to
    ///                     the following:
    ///                     \code
    ///                     bool pred(const Type1 &a, const Type1 &b);
    ///                     \endcode \n
    ///                     The signature does not need to have const &, but
    ///                     the function must not modify the objects passed to
    ///                     it. The type \a Type1 must be such that objects of
    ///                     type \a FwdIter can be dereferenced and then
    ///                     implicitly converted to \a Type1.
    /// \param proj         Specifies the function (or function object) which
    ///                     will be invoked for each of the elements as a
    ///                     projection operation before the actual predicate
    ///                     \a is invoked.
    ///
    /// The comparisons in the parallel \a max_element algorithm invoked with
    /// an execution policy object of type \a sequenced_policy
    /// execute in sequential order in the calling thread.
    ///
    /// The comparisons in the parallel \a max_element algorithm invoked with
    /// an execution policy object of type \a parallel_policy or
    /// \a parallel_task_policy are permitted to execute in an unordered
    /// fashion in unspecified threads, and indeterminately sequenced
    /// within each thread.
    ///
    /// \returns  The \a max_element algorithm returns a \a hpx::future<FwdIter>
    ///           if the execution policy is of type
    ///           \a sequenced_task_policy or
    ///           \a parallel_task_policy
    ///           and returns \a FwdIter otherwise.
    ///           The \a max_element algorithm returns the iterator to the
    ///           smallest element in the range [first, last). If several
    ///           elements in the range are equivalent to the smallest element,
    ///           returns the iterator to the first such element. Returns last
    ///           if the range is empty.
    ///
    template <typename ExPolicy, typename Rng,
        typename Proj = util::projection_identity,
        typename F = detail::less,
    HPX_CONCEPT_REQUIRES_(
        execution::is_execution_policy<ExPolicy>::value &&
        hpx::traits::is_range<Rng>::value &&
        traits::is_projected_range<Proj, Rng>::value &&
        traits::is_indirect_callable<
            ExPolicy, F,
                traits::projected_range<Proj, Rng>,
                traits::projected_range<Proj, Rng>
        >::value)>
    typename util::detail::algorithm_result<
        ExPolicy, typename hpx::traits::range_traits<Rng>::iterator_type
    >::type
    max_element(ExPolicy && policy, Rng && rng, F && f = F(),
        Proj && proj = Proj())
    {
        return max_element(std::forward<ExPolicy>(policy),
            hpx::util::begin(rng), hpx::util::end(rng),
            std::forward<F>(f), std::forward<Proj>(proj));
    }

    /// Finds the greatest element in the range [first, last) using the given
    /// comparison function \a f.
    ///
    /// \note   Complexity: At most \a max(floor(3/2*(N-1)), 0) applications of
    ///                     the predicate, where N = std::distance(first, last).
    ///
    /// \tparam ExPolicy    The type of the execution policy to use (deduced).
    ///                     It describes the manner in which the execution
    ///                     of the algorithm may be parallelized and the manner
    ///                     in which it executes the assignments.
    /// \tparam Rng         The type of the source range used (deduced).
    ///                     The iterators extracted from this range type must
    ///                     meet the requirements of an forward iterator.
    /// \tparam F           The type of the function/function object to use
    ///                     (deduced). Unlike its sequential form, the parallel
    ///                     overload of \a minmax_element requires \a F to meet the
    ///                     requirements of \a CopyConstructible.
    /// \tparam Proj        The type of an optional projection function. This
    ///                     defaults to \a util::projection_identity
    ///
    /// \param policy       The execution policy to use for the scheduling of
    ///                     the iterations.
    /// \param rng          Refers to the sequence of elements the algorithm
    ///                     will be applied to.
    /// \param f            The binary predicate which returns true if the
    ///                     the left argument is less than the right element.
    ///                     This argument is optional and defaults to std::less.
    ///                     The signature
    ///                     of the predicate function should be equivalent to
    ///                     the following:
    ///                     \code
    ///                     bool pred(const Type1 &a, const Type1 &b);
    ///                     \endcode \n
    ///                     The signature does not need to have const &, but
    ///                     the function must not modify the objects passed to
    ///                     it. The type \a Type1 must be such that objects of
    ///                     type \a FwdIter can be dereferenced and then
    ///                     implicitly converted to \a Type1.
    /// \param proj         Specifies the function (or function object) which
    ///                     will be invoked for each of the elements as a
    ///                     projection operation before the actual predicate
    ///                     \a is invoked.
    ///
    /// The comparisons in the parallel \a minmax_element algorithm invoked with
    /// an execution policy object of type \a sequenced_policy
    /// execute in sequential order in the calling thread.
    ///
    /// The comparisons in the parallel \a minmax_element algorithm invoked with
    /// an execution policy object of type \a parallel_policy or
    /// \a parallel_task_policy are permitted to execute in an unordered
    /// fashion in unspecified threads, and indeterminately sequenced
    /// within each thread.
    ///
    /// \returns  The \a minmax_element algorithm returns a
    /// \a hpx::future<tagged_pair<tag::min(FwdIter), tag::max(FwdIter)> >
    ///           if the execution policy is of type
    ///           \a sequenced_task_policy or
    ///           \a parallel_task_policy
    ///           and returns \a tagged_pair<tag::min(FwdIter), tag::max(FwdIter)>
    ///           otherwise.
    ///           The \a minmax_element algorithm returns a pair consisting of
    ///           an iterator to the smallest element as the first element and
    ///           an iterator to the greatest element as the second. Returns
    ///           std::make_pair(first, first) if the range is empty. If
    ///           several elements are equivalent to the smallest element, the
    ///           iterator to the first such element is returned. If several
    ///           elements are equivalent to the largest element, the iterator
    ///           to the last such element is returned.
    ///

#if defined(HPX_MSVC)
#pragma push_macro("min")
#pragma push_macro("max")
#undef min
#undef max
#endif

    template <typename ExPolicy, typename Rng,
        typename Proj = util::projection_identity,
        typename F = detail::less,
    HPX_CONCEPT_REQUIRES_(
        execution::is_execution_policy<ExPolicy>::value &&
        hpx::traits::is_range<Rng>::value &&
        traits::is_projected_range<Proj, Rng>::value &&
        traits::is_indirect_callable<
            ExPolicy, F,
                traits::projected_range<Proj, Rng>,
                traits::projected_range<Proj, Rng>
        >::value)>
    typename util::detail::algorithm_result<
        ExPolicy,
        hpx::util::tagged_pair<
            tag::min(typename hpx::traits::range_traits<Rng>::iterator_type),
            tag::max(typename hpx::traits::range_traits<Rng>::iterator_type)>
    >::type
    minmax_element(ExPolicy && policy, Rng && rng, F && f = F(),
        Proj && proj = Proj())
    {
        return minmax_element(std::forward<ExPolicy>(policy),
            hpx::util::begin(rng), hpx::util::end(rng),
            std::forward<F>(f), std::forward<Proj>(proj));
    }

#if defined(HPX_MSVC)
#pragma pop_macro("min")
#pragma pop_macro("max")
#endif
}}}

#endif