//===----------------------------------------------------------------------===//
//
// 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
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