libcxx/include/__algorithm/lexicographical_compare.h

   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-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___ALGORITHM_LEXICOGRAPHICAL_COMPARE_H
  10 #define _LIBCPP___ALGORITHM_LEXICOGRAPHICAL_COMPARE_H
  11
  12 #include <__algorithm/comp.h>
  13 #include <__algorithm/min.h>
  14 #include <__algorithm/mismatch.h>
  15 #include <__algorithm/simd_utils.h>
  16 #include <__algorithm/unwrap_iter.h>
  17 #include <__config>
  18 #include <__functional/identity.h>
  19 #include <__iterator/iterator_traits.h>
  20 #include <__string/constexpr_c_functions.h>
  21 #include <__type_traits/desugars_to.h>
  22 #include <__type_traits/enable_if.h>
  23 #include <__type_traits/invoke.h>
  24 #include <__type_traits/is_equality_comparable.h>
  25 #include <__type_traits/is_integral.h>
  26 #include <__type_traits/is_trivially_lexicographically_comparable.h>
  27 #include <__type_traits/is_volatile.h>
  28
  29 #if _LIBCPP_HAS_WIDE_CHARACTERS
  30 #  include <cwchar>
  31 #endif
  32
  33 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  34 #  pragma GCC system_header
  35 #endif
  36
  37 _LIBCPP_PUSH_MACROS
  38 #include <__undef_macros>
  39
  40 _LIBCPP_BEGIN_NAMESPACE_STD
  41
  42 template <class _Iter1, class _Sent1, class _Iter2, class _Sent2, class _Proj1, class _Proj2, class _Comp>
  43 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __lexicographical_compare(
  44     _Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Sent2 __last2, _Comp& __comp, _Proj1& __proj1, _Proj2& __proj2) {
  45   while (__first2 != __last2) {
  46     if (__first1 == __last1 ||
  47         std::__invoke(__comp, std::__invoke(__proj1, *__first1), std::__invoke(__proj2, *__first2)))
  48       return true;
  49     if (std::__invoke(__comp, std::__invoke(__proj2, *__first2), std::__invoke(__proj1, *__first1)))
  50       return false;
  51     ++__first1;
  52     ++__first2;
  53   }
  54   return false;
  55 }
  56
  57 #if _LIBCPP_STD_VER >= 14
  58
  59 // If the comparison operation is equivalent to < and that is a total order, we know that we can use equality comparison
  60 // on that type instead to extract some information. Furthermore, if equality comparison on that type is trivial, the
  61 // user can't observe that we're calling it. So instead of using the user-provided total order, we use std::mismatch,
  62 // which uses equality comparison (and is vertorized). Additionally, if the type is trivially lexicographically
  63 // comparable, we can go one step further and use std::memcmp directly instead of calling std::mismatch.
  64 template <class _Tp,
  65           class _Proj1,
  66           class _Proj2,
  67           class _Comp,
  68           __enable_if_t<__desugars_to_v<__totally_ordered_less_tag, _Comp, _Tp, _Tp> && !is_volatile<_Tp>::value &&
  69                             __libcpp_is_trivially_equality_comparable<_Tp, _Tp>::value &&
  70                             __is_identity<_Proj1>::value && __is_identity<_Proj2>::value,
  71                         int> = 0>
  72 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
  73 __lexicographical_compare(_Tp* __first1, _Tp* __last1, _Tp* __first2, _Tp* __last2, _Comp&, _Proj1&, _Proj2&) {
  74   if constexpr (__is_trivially_lexicographically_comparable_v<_Tp, _Tp>) {
  75     auto __res =
  76         std::__constexpr_memcmp(__first1, __first2, __element_count(std::min(__last1 - __first1, __last2 - __first2)));
  77     if (__res == 0)
  78       return __last1 - __first1 < __last2 - __first2;
  79     return __res < 0;
  80   }
  81 #  if _LIBCPP_HAS_WIDE_CHARACTERS
  82   else if constexpr (is_same<__remove_cv_t<_Tp>, wchar_t>::value) {
  83     auto __res = std::__constexpr_wmemcmp(__first1, __first2, std::min(__last1 - __first1, __last2 - __first2));
  84     if (__res == 0)
  85       return __last1 - __first1 < __last2 - __first2;
  86     return __res < 0;
  87   }
  88 #  endif // _LIBCPP_HAS_WIDE_CHARACTERS
  89   else {
  90     auto __res = std::mismatch(__first1, __last1, __first2, __last2);
  91     if (__res.second == __last2)
  92       return false;
  93     if (__res.first == __last1)
  94       return true;
  95     return *__res.first < *__res.second;
  96   }
  97 }
  98
  99 #endif // _LIBCPP_STD_VER >= 14
 100
 101 template <class _InputIterator1, class _InputIterator2, class _Compare>
 102 [[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool lexicographical_compare(
 103     _InputIterator1 __first1,
 104     _InputIterator1 __last1,
 105     _InputIterator2 __first2,
 106     _InputIterator2 __last2,
 107     _Compare __comp) {
 108   __identity __proj;
 109   return std::__lexicographical_compare(
 110       std::__unwrap_iter(__first1),
 111       std::__unwrap_iter(__last1),
 112       std::__unwrap_iter(__first2),
 113       std::__unwrap_iter(__last2),
 114       __comp,
 115       __proj,
 116       __proj);
 117 }
 118
 119 template <class _InputIterator1, class _InputIterator2>
 120 [[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool lexicographical_compare(
 121     _InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2) {
 122   return std::lexicographical_compare(__first1, __last1, __first2, __last2, __less<>());
 123 }
 124
 125 _LIBCPP_END_NAMESPACE_STD
 126
 127 _LIBCPP_POP_MACROS
 128
 129 #endif // _LIBCPP___ALGORITHM_LEXICOGRAPHICAL_COMPARE_H