257831582c
We were only checking that the comparator was rvalue callable, when in reality the algorithms always call comparators as lvalues. This patch also refactors the tests for callable requirements and expands it to a few missing algorithms. This is take 2 of #73451, which was reverted because it broke some CI bots. The issue was that we checked __is_callable with arguments in the wrong order inside std::upper_bound. This has now been fixed and a test was added. Fixes #69554
110 lines
5.1 KiB
C++
110 lines
5.1 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___ALGORITHM_LOWER_BOUND_H
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#define _LIBCPP___ALGORITHM_LOWER_BOUND_H
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#include <__algorithm/comp.h>
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#include <__algorithm/half_positive.h>
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#include <__algorithm/iterator_operations.h>
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#include <__config>
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#include <__functional/identity.h>
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#include <__functional/invoke.h>
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#include <__iterator/advance.h>
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#include <__iterator/distance.h>
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#include <__iterator/iterator_traits.h>
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#include <__type_traits/is_callable.h>
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#include <__type_traits/remove_reference.h>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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template <class _AlgPolicy, class _Iter, class _Type, class _Proj, class _Comp>
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_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Iter __lower_bound_bisecting(
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_Iter __first,
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const _Type& __value,
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typename iterator_traits<_Iter>::difference_type __len,
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_Comp& __comp,
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_Proj& __proj) {
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while (__len != 0) {
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auto __l2 = std::__half_positive(__len);
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_Iter __m = __first;
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_IterOps<_AlgPolicy>::advance(__m, __l2);
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if (std::__invoke(__comp, std::__invoke(__proj, *__m), __value)) {
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__first = ++__m;
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__len -= __l2 + 1;
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} else {
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__len = __l2;
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}
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}
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return __first;
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}
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// One-sided binary search, aka meta binary search, has been in the public domain for decades, and has the general
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// advantage of being \Omega(1) rather than the classic algorithm's \Omega(log(n)), with the downside of executing at
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// most 2*log(n) comparisons vs the classic algorithm's exact log(n). There are two scenarios in which it really shines:
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// the first one is when operating over non-random-access iterators, because the classic algorithm requires knowing the
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// container's size upfront, which adds \Omega(n) iterator increments to the complexity. The second one is when you're
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// traversing the container in order, trying to fast-forward to the next value: in that case, the classic algorithm
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// would yield \Omega(n*log(n)) comparisons and, for non-random-access iterators, \Omega(n^2) iterator increments,
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// whereas the one-sided version will yield O(n) operations on both counts, with a \Omega(log(n)) bound on the number of
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// comparisons.
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template <class _AlgPolicy, class _ForwardIterator, class _Sent, class _Type, class _Proj, class _Comp>
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_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
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__lower_bound_onesided(_ForwardIterator __first, _Sent __last, const _Type& __value, _Comp& __comp, _Proj& __proj) {
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// step = 0, ensuring we can always short-circuit when distance is 1 later on
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if (__first == __last || !std::__invoke(__comp, std::__invoke(__proj, *__first), __value))
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return __first;
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using _Distance = typename iterator_traits<_ForwardIterator>::difference_type;
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for (_Distance __step = 1; __first != __last; __step <<= 1) {
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auto __it = __first;
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auto __dist = __step - _IterOps<_AlgPolicy>::__advance_to(__it, __step, __last);
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// once we reach the last range where needle can be we must start
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// looking inwards, bisecting that range
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if (__it == __last || !std::__invoke(__comp, std::__invoke(__proj, *__it), __value)) {
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// we've already checked the previous value and it was less, we can save
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// one comparison by skipping bisection
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if (__dist == 1)
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return __it;
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return std::__lower_bound_bisecting<_AlgPolicy>(__first, __value, __dist, __comp, __proj);
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}
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// range not found, move forward!
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__first = __it;
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}
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return __first;
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}
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template <class _AlgPolicy, class _ForwardIterator, class _Sent, class _Type, class _Proj, class _Comp>
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_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
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__lower_bound(_ForwardIterator __first, _Sent __last, const _Type& __value, _Comp& __comp, _Proj& __proj) {
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const auto __dist = _IterOps<_AlgPolicy>::distance(__first, __last);
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return std::__lower_bound_bisecting<_AlgPolicy>(__first, __value, __dist, __comp, __proj);
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}
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template <class _ForwardIterator, class _Tp, class _Compare>
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_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
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lower_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value, _Compare __comp) {
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static_assert(__is_callable<_Compare&, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");
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auto __proj = std::__identity();
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return std::__lower_bound<_ClassicAlgPolicy>(__first, __last, __value, __comp, __proj);
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}
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template <class _ForwardIterator, class _Tp>
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_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
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lower_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
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return std::lower_bound(__first, __last, __value, __less<>());
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}
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___ALGORITHM_LOWER_BOUND_H
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