libcxx/include/__algorithm/set_intersection.h - llvm-project - Git at Google

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//

 #ifndef _LIBCPP___ALGORITHM_SET_INTERSECTION_H
 #define _LIBCPP___ALGORITHM_SET_INTERSECTION_H

 #include <__algorithm/comp.h>
 #include <__algorithm/comp_ref_type.h>
 #include <__algorithm/iterator_operations.h>
 #include <__algorithm/lower_bound.h>
 #include <__config>
 #include <__functional/identity.h>
 #include <__iterator/iterator_traits.h>
 #include <__iterator/next.h>
 #include <__type_traits/is_same.h>
 #include <__utility/exchange.h>
 #include <__utility/forward.h>
 #include <__utility/move.h>
 #include <__utility/swap.h>

 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif

 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>

 _LIBCPP_BEGIN_NAMESPACE_STD

 template <class _InIter1, class _InIter2, class _OutIter>
 struct __set_intersection_result {
   _InIter1 __in1_;
   _InIter2 __in2_;
   _OutIter __out_;

   // need a constructor as C++03 aggregate init is hard
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
   __set_intersection_result(_InIter1&& __in_iter1, _InIter2&& __in_iter2, _OutIter&& __out_iter)
       : __in1_(std::move(__in_iter1)), __in2_(std::move(__in_iter2)), __out_(std::move(__out_iter)) {}
 };

 // Helper for __set_intersection() with one-sided binary search: populate result and advance input iterators if they
 // are found to potentially contain the same value in two consecutive calls. This function is very intimately related to
 // the way it is used and doesn't attempt to abstract that, it's not appropriate for general usage outside of its
 // context.
 template <class _InForwardIter1, class _InForwardIter2, class _OutIter>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __set_intersection_add_output_if_equal(
     bool __may_be_equal,
     _InForwardIter1& __first1,
     _InForwardIter2& __first2,
     _OutIter& __result,
     bool& __prev_may_be_equal) {
   if (__may_be_equal && __prev_may_be_equal) {
     *__result = *__first1;
     ++__result;
     ++__first1;
     ++__first2;
     __prev_may_be_equal = false;
   } else {
     __prev_may_be_equal = __may_be_equal;
   }
 }

 // With forward iterators we can make multiple passes over the data, allowing the use of one-sided binary search to
 // reduce best-case complexity to log(N). Understanding how we can use binary search and still respect complexity
 // guarantees is _not_ straightforward: the guarantee is "at most 2*(N+M)-1 comparisons", and one-sided binary search
 // will necessarily overshoot depending on the position of the needle in the haystack -- for instance, if we're
 // searching for 3 in (1, 2, 3, 4), we'll check if 3<1, then 3<2, then 3<4, and, finally, 3<3, for a total of 4
 // comparisons, when linear search would have yielded 3. However, because we won't need to perform the intervening
 // reciprocal comparisons (ie 1<3, 2<3, 4<3), that extra comparison doesn't run afoul of the guarantee. Additionally,
 // this type of scenario can only happen for match distances of up to 5 elements, because 2*log2(8) is 6, and we'll
 // still be worse-off at position 5 of an 8-element set. From then onwards these scenarios can't happen. TL;DR: we'll be
 // 1 comparison worse-off compared to the classic linear-searching algorithm if matching position 3 of a set with 4
 // elements, or position 5 if the set has 7 or 8 elements, but we'll never exceed the complexity guarantees from the
 // standard.
 template <class _AlgPolicy,
           class _Compare,
           class _InForwardIter1,
           class _Sent1,
           class _InForwardIter2,
           class _Sent2,
           class _OutIter>
 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
 _LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InForwardIter1, _InForwardIter2, _OutIter>
 __set_intersection(
     _InForwardIter1 __first1,
     _Sent1 __last1,
     _InForwardIter2 __first2,
     _Sent2 __last2,
     _OutIter __result,
     _Compare&& __comp,
     std::forward_iterator_tag,
     std::forward_iterator_tag) {
   _LIBCPP_CONSTEXPR std::__identity __proj;
   bool __prev_may_be_equal = false;

   while (__first2 != __last2) {
     _InForwardIter1 __first1_next =
         std::__lower_bound_onesided<_AlgPolicy>(__first1, __last1, *__first2, __comp, __proj);
     std::swap(__first1_next, __first1);
     // keeping in mind that a==b iff !(a<b) && !(b<a):
     // if we can't advance __first1, that means !(*__first1 < *_first2), therefore __may_be_equal==true
     std::__set_intersection_add_output_if_equal(
         __first1 == __first1_next, __first1, __first2, __result, __prev_may_be_equal);
     if (__first1 == __last1)
       break;

     _InForwardIter2 __first2_next =
         std::__lower_bound_onesided<_AlgPolicy>(__first2, __last2, *__first1, __comp, __proj);
     std::swap(__first2_next, __first2);
     std::__set_intersection_add_output_if_equal(
         __first2 == __first2_next, __first1, __first2, __result, __prev_may_be_equal);
   }
   return __set_intersection_result<_InForwardIter1, _InForwardIter2, _OutIter>(
       _IterOps<_AlgPolicy>::next(std::move(__first1), std::move(__last1)),
       _IterOps<_AlgPolicy>::next(std::move(__first2), std::move(__last2)),
       std::move(__result));
 }

 // input iterators are not suitable for multipass algorithms, so we stick to the classic single-pass version
 template <class _AlgPolicy,
           class _Compare,
           class _InInputIter1,
           class _Sent1,
           class _InInputIter2,
           class _Sent2,
           class _OutIter>
 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
 _LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InInputIter1, _InInputIter2, _OutIter>
 __set_intersection(
     _InInputIter1 __first1,
     _Sent1 __last1,
     _InInputIter2 __first2,
     _Sent2 __last2,
     _OutIter __result,
     _Compare&& __comp,
     std::input_iterator_tag,
     std::input_iterator_tag) {
   while (__first1 != __last1 && __first2 != __last2) {
     if (__comp(*__first1, *__first2))
       ++__first1;
     else {
       if (!__comp(*__first2, *__first1)) {
         *__result = *__first1;
         ++__result;
         ++__first1;
       }
       ++__first2;
     }
   }

   return __set_intersection_result<_InInputIter1, _InInputIter2, _OutIter>(
       _IterOps<_AlgPolicy>::next(std::move(__first1), std::move(__last1)),
       _IterOps<_AlgPolicy>::next(std::move(__first2), std::move(__last2)),
       std::move(__result));
 }

 template <class _AlgPolicy, class _Compare, class _InIter1, class _Sent1, class _InIter2, class _Sent2, class _OutIter>
 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
 _LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InIter1, _InIter2, _OutIter>
 __set_intersection(
     _InIter1 __first1, _Sent1 __last1, _InIter2 __first2, _Sent2 __last2, _OutIter __result, _Compare&& __comp) {
   return std::__set_intersection<_AlgPolicy>(
       std::move(__first1),
       std::move(__last1),
       std::move(__first2),
       std::move(__last2),
       std::move(__result),
       std::forward<_Compare>(__comp),
       typename std::_IterOps<_AlgPolicy>::template __iterator_category<_InIter1>(),
       typename std::_IterOps<_AlgPolicy>::template __iterator_category<_InIter2>());
 }

 template <class _InputIterator1, class _InputIterator2, class _OutputIterator, class _Compare>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutputIterator set_intersection(
     _InputIterator1 __first1,
     _InputIterator1 __last1,
     _InputIterator2 __first2,
     _InputIterator2 __last2,
     _OutputIterator __result,
     _Compare __comp) {
   return std::__set_intersection<_ClassicAlgPolicy, __comp_ref_type<_Compare> >(
              std::move(__first1),
              std::move(__last1),
              std::move(__first2),
              std::move(__last2),
              std::move(__result),
              __comp)
       .__out_;
 }

 template <class _InputIterator1, class _InputIterator2, class _OutputIterator>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutputIterator set_intersection(
     _InputIterator1 __first1,
     _InputIterator1 __last1,
     _InputIterator2 __first2,
     _InputIterator2 __last2,
     _OutputIterator __result) {
   return std::__set_intersection<_ClassicAlgPolicy>(
              std::move(__first1),
              std::move(__last1),
              std::move(__first2),
              std::move(__last2),
              std::move(__result),
              __less<>())
       .__out_;
 }

 _LIBCPP_END_NAMESPACE_STD

 _LIBCPP_POP_MACROS

 #endif // _LIBCPP___ALGORITHM_SET_INTERSECTION_H
	//===----------------------------------------------------------------------===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//

	#ifndef _LIBCPP___ALGORITHM_SET_INTERSECTION_H
	#define _LIBCPP___ALGORITHM_SET_INTERSECTION_H

	#include <__algorithm/comp.h>
	#include <__algorithm/comp_ref_type.h>
	#include <__algorithm/iterator_operations.h>
	#include <__algorithm/lower_bound.h>
	#include <__config>
	#include <__functional/identity.h>
	#include <__iterator/iterator_traits.h>
	#include <__iterator/next.h>
	#include <__type_traits/is_same.h>
	#include <__utility/exchange.h>
	#include <__utility/forward.h>
	#include <__utility/move.h>
	#include <__utility/swap.h>

	#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
	# pragma GCC system_header
	#endif

	_LIBCPP_PUSH_MACROS
	#include <__undef_macros>

	_LIBCPP_BEGIN_NAMESPACE_STD

	template <class _InIter1, class _InIter2, class _OutIter>
	struct __set_intersection_result {
	_InIter1 __in1_;
	_InIter2 __in2_;
	_OutIter __out_;

	// need a constructor as C++03 aggregate init is hard
	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
	__set_intersection_result(_InIter1&& __in_iter1, _InIter2&& __in_iter2, _OutIter&& __out_iter)
	: __in1_(std::move(__in_iter1)), __in2_(std::move(__in_iter2)), __out_(std::move(__out_iter)) {}
	};

	// Helper for __set_intersection() with one-sided binary search: populate result and advance input iterators if they
	// are found to potentially contain the same value in two consecutive calls. This function is very intimately related to
	// the way it is used and doesn't attempt to abstract that, it's not appropriate for general usage outside of its
	// context.
	template <class _InForwardIter1, class _InForwardIter2, class _OutIter>
	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __set_intersection_add_output_if_equal(
	bool __may_be_equal,
	_InForwardIter1& __first1,
	_InForwardIter2& __first2,
	_OutIter& __result,
	bool& __prev_may_be_equal) {
	if (__may_be_equal && __prev_may_be_equal) {
	__result = __first1;
	++__result;
	++__first1;
	++__first2;
	__prev_may_be_equal = false;
	} else {
	__prev_may_be_equal = __may_be_equal;
	}
	}

	// With forward iterators we can make multiple passes over the data, allowing the use of one-sided binary search to
	// reduce best-case complexity to log(N). Understanding how we can use binary search and still respect complexity
	// guarantees is _not_ straightforward: the guarantee is "at most 2*(N+M)-1 comparisons", and one-sided binary search
	// will necessarily overshoot depending on the position of the needle in the haystack -- for instance, if we're
	// searching for 3 in (1, 2, 3, 4), we'll check if 3<1, then 3<2, then 3<4, and, finally, 3<3, for a total of 4
	// comparisons, when linear search would have yielded 3. However, because we won't need to perform the intervening
	// reciprocal comparisons (ie 1<3, 2<3, 4<3), that extra comparison doesn't run afoul of the guarantee. Additionally,
	// this type of scenario can only happen for match distances of up to 5 elements, because 2*log2(8) is 6, and we'll
	// still be worse-off at position 5 of an 8-element set. From then onwards these scenarios can't happen. TL;DR: we'll be
	// 1 comparison worse-off compared to the classic linear-searching algorithm if matching position 3 of a set with 4
	// elements, or position 5 if the set has 7 or 8 elements, but we'll never exceed the complexity guarantees from the
	// standard.
	template <class _AlgPolicy,
	class _Compare,
	class _InForwardIter1,
	class _Sent1,
	class _InForwardIter2,
	class _Sent2,
	class _OutIter>
	[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
	_LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InForwardIter1, _InForwardIter2, _OutIter>
	__set_intersection(
	_InForwardIter1 __first1,
	_Sent1 __last1,
	_InForwardIter2 __first2,
	_Sent2 __last2,
	_OutIter __result,
	_Compare&& __comp,
	std::forward_iterator_tag,
	std::forward_iterator_tag) {
	_LIBCPP_CONSTEXPR std::__identity __proj;
	bool __prev_may_be_equal = false;

	while (__first2 != __last2) {
	_InForwardIter1 __first1_next =
	std::__lower_bound_onesided<_AlgPolicy>(__first1, __last1, *__first2, __comp, __proj);
	std::swap(__first1_next, __first1);
	// keeping in mind that a==b iff !(a<b) && !(b<a):
	// if we can't advance __first1, that means !(__first1 < _first2), therefore __may_be_equal==true
	std::__set_intersection_add_output_if_equal(
	__first1 == __first1_next, __first1, __first2, __result, __prev_may_be_equal);
	if (__first1 == __last1)
	break;

	_InForwardIter2 __first2_next =
	std::__lower_bound_onesided<_AlgPolicy>(__first2, __last2, *__first1, __comp, __proj);
	std::swap(__first2_next, __first2);
	std::__set_intersection_add_output_if_equal(
	__first2 == __first2_next, __first1, __first2, __result, __prev_may_be_equal);
	}
	return __set_intersection_result<_InForwardIter1, _InForwardIter2, _OutIter>(
	_IterOps<_AlgPolicy>::next(std::move(__first1), std::move(__last1)),
	_IterOps<_AlgPolicy>::next(std::move(__first2), std::move(__last2)),
	std::move(__result));
	}

	// input iterators are not suitable for multipass algorithms, so we stick to the classic single-pass version
	template <class _AlgPolicy,
	class _Compare,
	class _InInputIter1,
	class _Sent1,
	class _InInputIter2,
	class _Sent2,
	class _OutIter>
	[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
	_LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InInputIter1, _InInputIter2, _OutIter>
	__set_intersection(
	_InInputIter1 __first1,
	_Sent1 __last1,
	_InInputIter2 __first2,
	_Sent2 __last2,
	_OutIter __result,
	_Compare&& __comp,
	std::input_iterator_tag,
	std::input_iterator_tag) {
	while (__first1 != __last1 && __first2 != __last2) {
	if (__comp(__first1, __first2))
	++__first1;
	else {
	if (!__comp(__first2, __first1)) {
	__result = __first1;
	++__result;
	++__first1;
	}
	++__first2;
	}
	}

	return __set_intersection_result<_InInputIter1, _InInputIter2, _OutIter>(
	_IterOps<_AlgPolicy>::next(std::move(__first1), std::move(__last1)),
	_IterOps<_AlgPolicy>::next(std::move(__first2), std::move(__last2)),
	std::move(__result));
	}

	template <class _AlgPolicy, class _Compare, class _InIter1, class _Sent1, class _InIter2, class _Sent2, class _OutIter>
	[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
	_LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InIter1, _InIter2, _OutIter>
	__set_intersection(
	_InIter1 __first1, _Sent1 __last1, _InIter2 __first2, _Sent2 __last2, _OutIter __result, _Compare&& __comp) {
	return std::__set_intersection<_AlgPolicy>(
	std::move(__first1),
	std::move(__last1),
	std::move(__first2),
	std::move(__last2),
	std::move(__result),
	std::forward<_Compare>(__comp),
	typename std::_IterOps<_AlgPolicy>::template __iterator_category<_InIter1>(),
	typename std::_IterOps<_AlgPolicy>::template __iterator_category<_InIter2>());
	}

	template <class _InputIterator1, class _InputIterator2, class _OutputIterator, class _Compare>
	inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutputIterator set_intersection(
	_InputIterator1 __first1,
	_InputIterator1 __last1,
	_InputIterator2 __first2,
	_InputIterator2 __last2,
	_OutputIterator __result,
	_Compare __comp) {
	return std::__set_intersection<_ClassicAlgPolicy, __comp_ref_type<_Compare> >(
	std::move(__first1),
	std::move(__last1),
	std::move(__first2),
	std::move(__last2),
	std::move(__result),
	__comp)
	.__out_;
	}

	template <class _InputIterator1, class _InputIterator2, class _OutputIterator>
	inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutputIterator set_intersection(
	_InputIterator1 __first1,
	_InputIterator1 __last1,
	_InputIterator2 __first2,
	_InputIterator2 __last2,
	_OutputIterator __result) {
	return std::__set_intersection<_ClassicAlgPolicy>(
	std::move(__first1),
	std::move(__last1),
	std::move(__first2),
	std::move(__last2),
	std::move(__result),
	__less<>())
	.__out_;
	}

	_LIBCPP_END_NAMESPACE_STD

	_LIBCPP_POP_MACROS

	#endif // _LIBCPP___ALGORITHM_SET_INTERSECTION_H