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Telegram/ThirdParty/range-v3/include/range/v3/view/sample.hpp

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+/// \file
+// Range v3 library
+//
+//  Copyright Casey Carter 2016
+//
+//  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
+//
+
+#ifndef RANGES_V3_VIEW_SAMPLE_HPP
+#define RANGES_V3_VIEW_SAMPLE_HPP
+
+#include <meta/meta.hpp>
+
+#include <range/v3/algorithm/shuffle.hpp>
+#include <range/v3/functional/bind_back.hpp>
+#include <range/v3/functional/invoke.hpp>
+#include <range/v3/iterator/concepts.hpp>
+#include <range/v3/iterator/default_sentinel.hpp>
+#include <range/v3/iterator/operations.hpp>
+#include <range/v3/range/concepts.hpp>
+#include <range/v3/utility/static_const.hpp>
+#include <range/v3/view/all.hpp>
+#include <range/v3/view/facade.hpp>
+#include <range/v3/view/view.hpp>
+
+#include <range/v3/detail/prologue.hpp>
+
+namespace ranges
+{
+    /// \cond
+    namespace detail
+    {
+        template<typename Rng,
+                 bool = (bool)sized_sentinel_for<sentinel_t<Rng>, iterator_t<Rng>>>
+        class size_tracker
+        {
+            range_difference_t<Rng> size_;
+
+        public:
+            CPP_assert(forward_range<Rng> || sized_range<Rng>);
+            size_tracker() = default;
+            size_tracker(Rng & rng)
+              : size_(ranges::distance(rng))
+            {}
+            void decrement()
+            {
+                --size_;
+            }
+            range_difference_t<Rng> get(Rng &, iterator_t<Rng> &) const
+            {
+                return size_;
+            }
+        };
+
+        // Impl for sized_sentinel_for (no need to store anything)
+        template<typename Rng>
+        class size_tracker<Rng, true>
+        {
+        public:
+            size_tracker() = default;
+            size_tracker(Rng &)
+            {}
+            void decrement()
+            {}
+            range_difference_t<Rng> get(Rng & rng, iterator_t<Rng> const & it) const
+            {
+                return ranges::end(rng) - it;
+            }
+        };
+    } // namespace detail
+    /// \endcond
+
+    /// \addtogroup group-views
+    /// @{
+
+    // Take a random sampling from another view
+    template<typename Rng, typename URNG>
+    class sample_view : public view_facade<sample_view<Rng, URNG>, finite>
+    {
+        friend range_access;
+        using D = range_difference_t<Rng>;
+        Rng rng_;
+        // Mutable is OK here because sample_view is an Input view.
+        mutable range_difference_t<Rng> size_;
+        URNG * engine_;
+
+        template<bool IsConst>
+        class cursor
+        {
+            friend cursor<!IsConst>;
+
+            using Base = meta::const_if_c<IsConst, Rng>;
+            meta::const_if_c<IsConst, sample_view> * parent_;
+            iterator_t<Base> current_;
+            RANGES_NO_UNIQUE_ADDRESS detail::size_tracker<Base> size_;
+
+            D pop_size()
+            {
+                return size_.get(parent_->rng_, current_);
+            }
+            void advance()
+            {
+                if(parent_->size_ > 0)
+                {
+                    using Dist = std::uniform_int_distribution<D>;
+                    Dist dist{};
+                    URNG & engine = *parent_->engine_;
+
+                    for(;; ++current_, size_.decrement())
+                    {
+                        RANGES_ASSERT(current_ != ranges::end(parent_->rng_));
+                        auto n = pop_size();
+                        RANGES_EXPECT(n > 0);
+                        typename Dist::param_type const interval{0, n - 1};
+                        if(dist(engine, interval) < parent_->size_)
+                            break;
+                    }
+                }
+            }
+
+        public:
+            using value_type = range_value_t<Rng>;
+            using difference_type = D;
+
+            cursor() = default;
+            explicit cursor(meta::const_if_c<IsConst, sample_view> * rng)
+              : parent_(rng)
+              , current_(ranges::begin(rng->rng_))
+              , size_{rng->rng_}
+            {
+                auto n = pop_size();
+                if(rng->size_ > n)
+                    rng->size_ = n;
+                advance();
+            }
+            template(bool Other)(
+                requires IsConst AND CPP_NOT(Other)) //
+            cursor(cursor<Other> that)
+              : parent_(that.parent_)
+              , current_(std::move(that.current_))
+              , size_(that.size_)
+            {}
+            range_reference_t<Rng> read() const
+            {
+                return *current_;
+            }
+            bool equal(default_sentinel_t) const
+            {
+                RANGES_EXPECT(parent_);
+                return parent_->size_ <= 0;
+            }
+            void next()
+            {
+                RANGES_EXPECT(parent_);
+                RANGES_EXPECT(parent_->size_ > 0);
+                --parent_->size_;
+                RANGES_ASSERT(current_ != ranges::end(parent_->rng_));
+                ++current_;
+                size_.decrement();
+                advance();
+            }
+        };
+
+        cursor<false> begin_cursor()
+        {
+            return cursor<false>{this};
+        }
+        template(bool Const = true)(
+            requires Const AND
+            (sized_range<meta::const_if_c<Const, Rng>> ||
+             sized_sentinel_for<sentinel_t<meta::const_if_c<Const, Rng>>,
+                                iterator_t<meta::const_if_c<Const, Rng>>> ||
+             forward_range<meta::const_if_c<Const, Rng>>)) //
+        cursor<Const> begin_cursor() const
+        {
+            return cursor<true>{this};
+        }
+
+    public:
+        sample_view() = default;
+
+        explicit sample_view(Rng rng, D sample_size, URNG & generator)
+          : rng_(std::move(rng))
+          , size_(sample_size)
+          , engine_(std::addressof(generator))
+        {
+            RANGES_EXPECT(sample_size >= 0);
+        }
+
+        Rng base() const
+        {
+            return rng_;
+        }
+    };
+
+#if RANGES_CXX_DEDUCTION_GUIDES >= RANGES_CXX_DEDUCTION_GUIDES_17
+    template<typename Rng, typename URNG>
+    sample_view(Rng &&, range_difference_t<Rng>, URNG &)
+        ->sample_view<views::all_t<Rng>, URNG>;
+#endif
+
+    namespace views
+    {
+        /// Returns a random sample of a range of length `size(range)`.
+        struct sample_base_fn
+        {
+            template(typename Rng, typename URNG = detail::default_random_engine)(
+                requires viewable_range<Rng> AND input_range<Rng> AND
+                    uniform_random_bit_generator<URNG> AND
+                    convertible_to<invoke_result_t<URNG &>, range_difference_t<Rng>> AND
+                    (sized_range<Rng> ||
+                     sized_sentinel_for<sentinel_t<Rng>, iterator_t<Rng>> ||
+                     forward_range<Rng>)) //
+            sample_view<all_t<Rng>, URNG> operator()(
+                Rng && rng,
+                range_difference_t<Rng> sample_size,
+                URNG & generator = detail::get_random_engine()) const
+            {
+                return sample_view<all_t<Rng>, URNG>{
+                    all(static_cast<Rng &&>(rng)), sample_size, generator};
+            }
+
+            /// \cond
+            template<typename Rng, typename URNG>
+            invoke_result_t<sample_base_fn, Rng, range_difference_t<Rng>, URNG &> //
+            operator()(
+                Rng && rng,
+                range_difference_t<Rng> sample_size,
+                detail::reference_wrapper_<URNG> r) const
+            {
+                return (*this)(static_cast<Rng &&>(rng), sample_size, r.get());
+            }
+            /// \endcond
+        };
+
+        struct sample_fn : sample_base_fn
+        {
+            using sample_base_fn::operator();
+
+            template(typename Size, typename URNG = detail::default_random_engine)(
+                requires integral<Size> AND uniform_random_bit_generator<URNG>)
+            constexpr auto operator()(
+                Size n,
+                URNG & urng = detail::get_random_engine()) const //
+            {
+                return make_view_closure(bind_back(
+                    sample_base_fn{}, n, detail::reference_wrapper_<URNG>(urng)));
+            }
+        };
+
+        /// \relates sample_fn
+        /// \ingroup group-views
+        RANGES_INLINE_VARIABLE(sample_fn, sample)
+    } // namespace views
+    /// @}
+} // namespace ranges
+
+#include <range/v3/detail/epilogue.hpp>
+#include <range/v3/detail/satisfy_boost_range.hpp>
+RANGES_SATISFY_BOOST_RANGE(::ranges::sample_view)
+
+#endif