search_n.hpp

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// Range v3 library
//
//  Copyright Eric Niebler 2014-present
//
//  Use, modification and distribution is subject to 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)
//
// Project home: https://github.com/ericniebler/range-v3
//
//===----------------------------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef RANGES_V3_ALGORITHM_SEARCH_N_HPP
#define RANGES_V3_ALGORITHM_SEARCH_N_HPP
 
#include <meta/meta.hpp>
 
#include <range/v3/range_fwd.hpp>
 
#include <range/v3/functional/comparisons.hpp>
#include <range/v3/functional/identity.hpp>
#include <range/v3/functional/invoke.hpp>
#include <range/v3/iterator/concepts.hpp>
#include <range/v3/iterator/operations.hpp>
#include <range/v3/iterator/traits.hpp>
#include <range/v3/range/access.hpp>
#include <range/v3/range/concepts.hpp>
#include <range/v3/range/primitives.hpp>
#include <range/v3/range/traits.hpp>
#include <range/v3/utility/static_const.hpp>
#include <range/v3/view/subrange.hpp>
 
#include <range/v3/detail/prologue.hpp>
 
namespace ranges
{

    namespace detail
    {
        template<typename I, typename S, typename D, typename V, typename C, typename P>
        constexpr subrange<I> search_n_sized_impl(I const begin_, 
                                                  S last, 
                                                  D const d_, 
                                                  D cnt,
                                                  V const & val, 
                                                  C & pred, 
                                                  P & proj)
        {
            D d = d_; // always the distance from first to end
            auto first = uncounted(begin_);
            while(true)
            {
                // Find first element in sequence 1 that matches val, with a mininum of
                // loop checks
                while(true)
                {
                    if(d < cnt) // return the last if we've run out of room
                    {
                        auto e = ranges::next(recounted(begin_, std::move(first), d_ - d),
                                              std::move(last));
                        return {e, e};
                    }
                    if(invoke(pred, invoke(proj, *first), val))
                        break;
                    ++first;
                    --d;
                }
                // *first matches val, now match elements after here
                auto m = first;
                D c = 0;
                while(true)
                {
                    if(++c == cnt) // If pattern exhausted, first is the answer (works
                                   // for 1 element pattern)
                        return {recounted(begin_, std::move(first), d_ - d),
                                recounted(begin_, std::move(++m), d_ - d)};
                    ++m; // No need to check, we know we have room to match successfully
                    if(!invoke(pred,
                               invoke(proj, *m),
                               val)) // if there is a mismatch, restart with a new begin
                    {
                        first = next(std::move(m));
                        d -= (c + 1);
                        break;
                    } // else there is a match, check next elements
                }
            }
        }
 
        template<typename I, typename S, typename D, typename V, typename C, typename P>
        constexpr subrange<I> search_n_impl(I first, 
                                            S last, 
                                            D cnt, 
                                            V const & val, 
                                            C & pred,
                                            P & proj)
        {
            while(true)
            {
                // Find first element in sequence 1 that matches val, with a mininum of
                // loop checks
                while(true)
                {
                    if(first == last) // return last if no element matches val
                        return {first, first};
                    if(invoke(pred, invoke(proj, *first), val))
                        break;
                    ++first;
                }
                // *first matches val, now match elements after here
                I m = first;
                D c = 0;
                while(true)
                {
                    if(++c == cnt) // If pattern exhausted, first is the answer (works
                                   // for 1 element pattern)
                        return {first, ++m};
                    if(++m == last) // Otherwise if source exhausted, pattern not found
                        return {m, m};
                    if(!invoke(pred,
                               invoke(proj, *m),
                               val)) // if there is a mismatch, restart with a new begin
                    {
                        first = next(std::move(m));
                        break;
                    } // else there is a match, check next elements
                }
            }
        }
    } // namespace detail
 
    RANGES_FUNC_BEGIN(search_n)
 
        
        template(typename I,
                 typename S,
                 typename V,
                 typename C = equal_to,
                 typename P = identity)(
            requires forward_iterator<I> AND sentinel_for<S, I> AND
                indirectly_comparable<I, V const *, C, P>)
        constexpr subrange<I> RANGES_FUNC(search_n)(I first,
                                                    S last,
                                                    iter_difference_t<I> cnt,
                                                    V const & val,
                                                    C pred = C{},
                                                    P proj = P{}) //
        {
            if(cnt <= 0)
                return {first, first};
            if(RANGES_CONSTEXPR_IF(sized_sentinel_for<S, I>))
                return detail::search_n_sized_impl(std::move(first),
                                                   std::move(last),
                                                   distance(first, last),
                                                   cnt,
                                                   val,
                                                   pred,
                                                   proj);
            else
                return detail::search_n_impl(
                    std::move(first), std::move(last), cnt, val, pred, proj);
        }

        template(typename Rng, typename V, typename C = equal_to, typename P = identity)(
            requires forward_range<Rng> AND
                indirectly_comparable<iterator_t<Rng>, V const *, C, P>)
        constexpr borrowed_subrange_t<Rng> RANGES_FUNC(search_n)(Rng && rng,
                                                                 iter_difference_t<iterator_t<Rng>> cnt,
                                                                 V const & val,
                                                                 C pred = C{},
                                                                 P proj = P{}) //
        {
            if(cnt <= 0)
                return subrange<iterator_t<Rng>>{begin(rng), begin(rng)};
            if(RANGES_CONSTEXPR_IF(sized_range<Rng>))
                return detail::search_n_sized_impl(
                    begin(rng), end(rng), distance(rng), cnt, val, pred, proj);
            else
                return detail::search_n_impl(begin(rng), end(rng), cnt, val, pred, proj);
        }
 
    RANGES_FUNC_END(search_n)
 
    namespace cpp20
    {
        using ranges::search_n;
    }
} // namespace ranges
 
#include <range/v3/detail/epilogue.hpp>
 
#endif