find_if.hpp

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/*=============================================================================
    Copyright (c) 2001-2006 Joel de Guzman
    Copyright (c) 2007 Dan Marsden

    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)
==============================================================================*/
#if !defined(FUSION_FIND_IF_05052005_1107)
#define FUSION_FIND_IF_05052005_1107

#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/or.hpp>
#include <boost/mpl/lambda.hpp>
#include <boost/mpl/apply.hpp>
#include <boost/mpl/identity.hpp>
#include <boost/fusion/iterator/value_of.hpp>
#include <boost/fusion/iterator/equal_to.hpp>
#include <boost/fusion/iterator/next.hpp>
#include <boost/fusion/sequence/intrinsic/begin.hpp>
#include <boost/fusion/iterator/advance.hpp>
#include <boost/fusion/iterator/distance.hpp>
#include <boost/fusion/support/category_of.hpp>
#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/identity.hpp>

namespace boost { namespace fusion { 
    struct random_access_traversal_tag;
namespace detail
{
    template <typename Iterator, typename Pred>
    struct apply_filter
    {
        typedef typename mpl::apply1<
            Pred, typename result_of::value_of<Iterator>::type>::type type;
        BOOST_STATIC_CONSTANT(int, value = type::value);
    };

    template <typename First, typename Last, typename Pred>
    struct main_find_if;

    template <typename First, typename Last, typename Pred>
    struct recursive_find_if
    {
        typedef typename
            main_find_if<
                typename result_of::next<First>::type, Last, Pred
            >::type
        type;
    };

    template <typename First, typename Last, typename Pred>
    struct main_find_if
    {
        typedef mpl::or_<
            result_of::equal_to<First, Last>
          , apply_filter<First, Pred> >
        filter;

        typedef typename
            mpl::eval_if<
                filter
              , mpl::identity<First>
              , recursive_find_if<First, Last, Pred>
            >::type
        type;
    };

    template<
        typename First, typename Last, 
        typename Pred, bool>
    struct choose_find_if;

    template<typename First, typename Last, typename Pred>
    struct choose_find_if<First, Last, Pred, false>
        : main_find_if<First, Last, Pred>
    {};

    template<typename Iter, typename Pred, int n, int unrolling>
    struct unroll_again;

    template <typename Iter, typename Pred, int offset>
    struct apply_offset_filter
    {
        typedef typename result_of::advance_c<Iter, offset>::type Shifted;
        typedef typename
            mpl::apply1<
                Pred
              , typename result_of::value_of<Shifted>::type
            >::type
        type;
        BOOST_STATIC_CONSTANT(int, value = type::value);
    };

    template<typename Iter, typename Pred, int n>
    struct unrolled_find_if
    {
        typedef typename mpl::eval_if<
            apply_filter<Iter, Pred>,
            mpl::identity<Iter>,
            mpl::eval_if<
              apply_offset_filter<Iter, Pred, 1>,
              result_of::advance_c<Iter, 1>,
              mpl::eval_if<
                apply_offset_filter<Iter, Pred, 2>,
                result_of::advance_c<Iter, 2>,
                mpl::eval_if<
                  apply_offset_filter<Iter, Pred, 3>,
                  result_of::advance_c<Iter, 3>,
                  unroll_again<
                    Iter,
                    Pred,
                    n,
                    4> > > > >::type type;
    };

    template<typename Iter, typename Pred>
    struct unrolled_find_if<Iter, Pred, 3>
    {
        typedef typename mpl::eval_if<
            apply_filter<Iter, Pred>,
            mpl::identity<Iter>,
            mpl::eval_if<
              apply_offset_filter<Iter, Pred, 1>,
              result_of::advance_c<Iter, 1>,
              mpl::eval_if<
                apply_offset_filter<Iter, Pred, 2>,
                result_of::advance_c<Iter, 2>,
                result_of::advance_c<Iter, 3> > > >::type type;
    };

    template<typename Iter, typename Pred>
    struct unrolled_find_if<Iter, Pred, 2>
    {
        typedef typename mpl::eval_if<
            apply_filter<Iter, Pred>,
            mpl::identity<Iter>,
            mpl::eval_if<
              apply_offset_filter<Iter, Pred, 1>,
              result_of::advance_c<Iter, 1>,
              result_of::advance_c<Iter, 2> > >::type type;
    };

    template<typename Iter, typename Pred>
    struct unrolled_find_if<Iter, Pred, 1>
    {
        typedef typename mpl::eval_if<
            apply_filter<Iter, Pred>,
            mpl::identity<Iter>,
            result_of::advance_c<Iter, 1> >::type type;
    };

    template<typename Iter, typename Pred, int n, int unrolling>
    struct unroll_again
    {
        typedef typename unrolled_find_if<
            typename result_of::advance_c<Iter, unrolling>::type,
            Pred,
            n-unrolling>::type type;
    };

    template<typename Iter, typename Pred>
    struct unrolled_find_if<Iter, Pred, 0>
    {
        typedef Iter type;
    };

    template<typename First, typename Last, typename Pred>
    struct choose_find_if<First, Last, Pred, true>
    {
        typedef typename result_of::distance<First, Last>::type N;
        typedef typename unrolled_find_if<First, Pred, N::value>::type type;
    };

    template <typename First, typename Last, typename Pred>
    struct static_find_if
    {
        typedef typename
            choose_find_if<
                First
              , Last
              , typename mpl::lambda<Pred>::type
              , is_base_of<random_access_traversal_tag, typename traits::category_of<First>::type>::value
            >::type
        type;

        template <typename Iterator>
        static type
        recursive_call(Iterator const& iter, mpl::true_)
        {
            return iter;
        }

        template <typename Iterator>
        static type
        recursive_call(Iterator const& iter, mpl::false_)
        {
            return recursive_call(fusion::next(iter));
        }

        template <typename Iterator>
        static type
        recursive_call(Iterator const& iter)
        {
            typedef result_of::equal_to<Iterator, type> found;
            return recursive_call(iter, found());
        }

        template <typename Iterator, typename Tag>
        static type
        choose_call(Iterator const& iter, Tag)
        {
            return recursive_call(iter);
        }

        template <typename Iterator>
        static type
        choose_call(Iterator const& iter, random_access_traversal_tag)
        {
            typedef typename result_of::distance<Iterator, type>::type N;
            return fusion::advance<N>(iter);
        }

        template <typename Iterator>
        static type
        call(Iterator const& iter)
        {
            return choose_call(iter, typename traits::category_of<Iterator>::type());
        }
    };

    template <typename First, typename Last, typename Pred>
    struct static_seq_find_if : static_find_if<First, Last, Pred>
    {
        typedef typename static_find_if<First, Last, Pred>::type type;

        template <typename Sequence>
        static type
        call(Sequence const& seq)
        {
            return static_find_if<First, Last, Pred>::call(fusion::begin(seq));
        }

        template <typename Sequence>
        static type
        call(Sequence& seq)
        {
            return static_find_if<First, Last, Pred>::call(fusion::begin(seq));
        }
    };
}}}

#endif