libcxx/include/__algorithm/find_segment_if.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_FIND_SEGMENT_IF_H
  10 #define _LIBCPP___ALGORITHM_FIND_SEGMENT_IF_H
  11
  12 #include <__config>
  13 #include <__iterator/segmented_iterator.h>
  14
  15 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  16 #  pragma GCC system_header
  17 #endif
  18
  19 _LIBCPP_BEGIN_NAMESPACE_STD
  20
  21 // __find_segment_if is a utility function for optimizing iteration over segmented iterators linearly.
  22 // [__first, __last) has to be a segmented range. __pred is expected to take a range of local iterators and the __proj.
  23 // It returns an iterator to the first element that satisfies the predicate, or a one-past-the-end iterator if there was
  24 // no match. __proj may be anything that should be passed to __pred, but is expected to be a projection to support
  25 // ranges algorithms, or __identity for classic algorithms.
  26
  27 template <class _SegmentedIterator, class _Pred, class _Proj>
  28 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _SegmentedIterator
  29 __find_segment_if(_SegmentedIterator __first, _SegmentedIterator __last, _Pred __pred, _Proj& __proj) {
  30   using _Traits = __segmented_iterator_traits<_SegmentedIterator>;
  31
  32   auto __sfirst = _Traits::__segment(__first);
  33   auto __slast  = _Traits::__segment(__last);
  34
  35   // We are in a single segment, so we might not be at the beginning or end
  36   if (__sfirst == __slast)
  37     return _Traits::__compose(__sfirst, __pred(_Traits::__local(__first), _Traits::__local(__last), __proj));
  38
  39   { // We have more than one segment. Iterate over the first segment, since we might not start at the beginning
  40     auto __llast = _Traits::__end(__sfirst);
  41     auto __liter = __pred(_Traits::__local(__first), __llast, __proj);
  42     if (__liter != __llast)
  43       return _Traits::__compose(__sfirst, __liter);
  44   }
  45   ++__sfirst;
  46
  47   // Iterate over the segments which are guaranteed to be completely in the range
  48   while (__sfirst != __slast) {
  49     auto __llast = _Traits::__end(__sfirst);
  50     auto __liter = __pred(_Traits::__begin(__sfirst), _Traits::__end(__sfirst), __proj);
  51     if (__liter != __llast)
  52       return _Traits::__compose(__sfirst, __liter);
  53     ++__sfirst;
  54   }
  55
  56   // Iterate over the last segment
  57   return _Traits::__compose(__sfirst, __pred(_Traits::__begin(__sfirst), _Traits::__local(__last), __proj));
  58 }
  59
  60 _LIBCPP_END_NAMESPACE_STD
  61
  62 #endif // _LIBCPP___ALGORITHM_FIND_SEGMENT_IF_H