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1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP___CXX03___ALGORITHM_SET_INTERSECTION_H10#define _LIBCPP___CXX03___ALGORITHM_SET_INTERSECTION_H11 12#include <__cxx03/__algorithm/comp.h>13#include <__cxx03/__algorithm/comp_ref_type.h>14#include <__cxx03/__algorithm/iterator_operations.h>15#include <__cxx03/__algorithm/lower_bound.h>16#include <__cxx03/__config>17#include <__cxx03/__functional/identity.h>18#include <__cxx03/__iterator/iterator_traits.h>19#include <__cxx03/__iterator/next.h>20#include <__cxx03/__type_traits/is_same.h>21#include <__cxx03/__utility/move.h>22#include <__cxx03/__utility/swap.h>23 24#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)25# pragma GCC system_header26#endif27 28_LIBCPP_PUSH_MACROS29#include <__cxx03/__undef_macros>30 31_LIBCPP_BEGIN_NAMESPACE_STD32 33template <class _InIter1, class _InIter2, class _OutIter>34struct __set_intersection_result {35 _InIter1 __in1_;36 _InIter2 __in2_;37 _OutIter __out_;38 39 // need a constructor as C++03 aggregate init is hard40 _LIBCPP_HIDE_FROM_ABI __set_intersection_result(_InIter1&& __in_iter1, _InIter2&& __in_iter2, _OutIter&& __out_iter)41 : __in1_(std::move(__in_iter1)), __in2_(std::move(__in_iter2)), __out_(std::move(__out_iter)) {}42};43 44// Helper for __set_intersection() with one-sided binary search: populate result and advance input iterators if they45// are found to potentially contain the same value in two consecutive calls. This function is very intimately related to46// the way it is used and doesn't attempt to abstract that, it's not appropriate for general usage outside of its47// context.48template <class _InForwardIter1, class _InForwardIter2, class _OutIter>49_LIBCPP_HIDE_FROM_ABI void __set_intersection_add_output_if_equal(50 bool __may_be_equal,51 _InForwardIter1& __first1,52 _InForwardIter2& __first2,53 _OutIter& __result,54 bool& __prev_may_be_equal) {55 if (__may_be_equal && __prev_may_be_equal) {56 *__result = *__first1;57 ++__result;58 ++__first1;59 ++__first2;60 __prev_may_be_equal = false;61 } else {62 __prev_may_be_equal = __may_be_equal;63 }64}65 66// With forward iterators we can make multiple passes over the data, allowing the use of one-sided binary search to67// reduce best-case complexity to log(N). Understanding how we can use binary search and still respect complexity68// guarantees is _not_ straightforward: the guarantee is "at most 2*(N+M)-1 comparisons", and one-sided binary search69// will necessarily overshoot depending on the position of the needle in the haystack -- for instance, if we're70// 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 471// comparisons, when linear search would have yielded 3. However, because we won't need to perform the intervening72// reciprocal comparisons (ie 1<3, 2<3, 4<3), that extra comparison doesn't run afoul of the guarantee. Additionally,73// this type of scenario can only happen for match distances of up to 5 elements, because 2*log2(8) is 6, and we'll74// still be worse-off at position 5 of an 8-element set. From then onwards these scenarios can't happen. TL;DR: we'll be75// 1 comparison worse-off compared to the classic linear-searching algorithm if matching position 3 of a set with 476// elements, or position 5 if the set has 7 or 8 elements, but we'll never exceed the complexity guarantees from the77// standard.78template <class _AlgPolicy,79 class _Compare,80 class _InForwardIter1,81 class _Sent1,82 class _InForwardIter2,83 class _Sent2,84 class _OutIter>85_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI __set_intersection_result<_InForwardIter1, _InForwardIter2, _OutIter>86__set_intersection(87 _InForwardIter1 __first1,88 _Sent1 __last1,89 _InForwardIter2 __first2,90 _Sent2 __last2,91 _OutIter __result,92 _Compare&& __comp,93 std::forward_iterator_tag,94 std::forward_iterator_tag) {95 std::__identity __proj;96 bool __prev_may_be_equal = false;97 98 while (__first2 != __last2) {99 _InForwardIter1 __first1_next =100 std::__lower_bound_onesided<_AlgPolicy>(__first1, __last1, *__first2, __comp, __proj);101 std::swap(__first1_next, __first1);102 // keeping in mind that a==b iff !(a<b) && !(b<a):103 // if we can't advance __first1, that means !(*__first1 < *_first2), therefore __may_be_equal==true104 std::__set_intersection_add_output_if_equal(105 __first1 == __first1_next, __first1, __first2, __result, __prev_may_be_equal);106 if (__first1 == __last1)107 break;108 109 _InForwardIter2 __first2_next =110 std::__lower_bound_onesided<_AlgPolicy>(__first2, __last2, *__first1, __comp, __proj);111 std::swap(__first2_next, __first2);112 std::__set_intersection_add_output_if_equal(113 __first2 == __first2_next, __first1, __first2, __result, __prev_may_be_equal);114 }115 return __set_intersection_result<_InForwardIter1, _InForwardIter2, _OutIter>(116 _IterOps<_AlgPolicy>::next(std::move(__first1), std::move(__last1)),117 _IterOps<_AlgPolicy>::next(std::move(__first2), std::move(__last2)),118 std::move(__result));119}120 121// input iterators are not suitable for multipass algorithms, so we stick to the classic single-pass version122template <class _AlgPolicy,123 class _Compare,124 class _InInputIter1,125 class _Sent1,126 class _InInputIter2,127 class _Sent2,128 class _OutIter>129_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI __set_intersection_result<_InInputIter1, _InInputIter2, _OutIter>130__set_intersection(131 _InInputIter1 __first1,132 _Sent1 __last1,133 _InInputIter2 __first2,134 _Sent2 __last2,135 _OutIter __result,136 _Compare&& __comp,137 std::input_iterator_tag,138 std::input_iterator_tag) {139 while (__first1 != __last1 && __first2 != __last2) {140 if (__comp(*__first1, *__first2))141 ++__first1;142 else {143 if (!__comp(*__first2, *__first1)) {144 *__result = *__first1;145 ++__result;146 ++__first1;147 }148 ++__first2;149 }150 }151 152 return __set_intersection_result<_InInputIter1, _InInputIter2, _OutIter>(153 _IterOps<_AlgPolicy>::next(std::move(__first1), std::move(__last1)),154 _IterOps<_AlgPolicy>::next(std::move(__first2), std::move(__last2)),155 std::move(__result));156}157 158template <class _AlgPolicy, class _Compare, class _InIter1, class _Sent1, class _InIter2, class _Sent2, class _OutIter>159_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI __set_intersection_result<_InIter1, _InIter2, _OutIter> __set_intersection(160 _InIter1 __first1, _Sent1 __last1, _InIter2 __first2, _Sent2 __last2, _OutIter __result, _Compare&& __comp) {161 return std::__set_intersection<_AlgPolicy>(162 std::move(__first1),163 std::move(__last1),164 std::move(__first2),165 std::move(__last2),166 std::move(__result),167 std::forward<_Compare>(__comp),168 typename std::_IterOps<_AlgPolicy>::template __iterator_category<_InIter1>(),169 typename std::_IterOps<_AlgPolicy>::template __iterator_category<_InIter2>());170}171 172template <class _InputIterator1, class _InputIterator2, class _OutputIterator, class _Compare>173inline _LIBCPP_HIDE_FROM_ABI _OutputIterator set_intersection(174 _InputIterator1 __first1,175 _InputIterator1 __last1,176 _InputIterator2 __first2,177 _InputIterator2 __last2,178 _OutputIterator __result,179 _Compare __comp) {180 return std::__set_intersection<_ClassicAlgPolicy, __comp_ref_type<_Compare> >(181 std::move(__first1),182 std::move(__last1),183 std::move(__first2),184 std::move(__last2),185 std::move(__result),186 __comp)187 .__out_;188}189 190template <class _InputIterator1, class _InputIterator2, class _OutputIterator>191inline _LIBCPP_HIDE_FROM_ABI _OutputIterator set_intersection(192 _InputIterator1 __first1,193 _InputIterator1 __last1,194 _InputIterator2 __first2,195 _InputIterator2 __last2,196 _OutputIterator __result) {197 return std::__set_intersection<_ClassicAlgPolicy>(198 std::move(__first1),199 std::move(__last1),200 std::move(__first2),201 std::move(__last2),202 std::move(__result),203 __less<>())204 .__out_;205}206 207_LIBCPP_END_NAMESPACE_STD208 209_LIBCPP_POP_MACROS210 211#endif // _LIBCPP___CXX03___ALGORITHM_SET_INTERSECTION_H212