libcxx/include/__cxx03/__algorithm/for_each_segment.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_FOR_EACH_SEGMENT_H
  10 #define _LIBCPP___ALGORITHM_FOR_EACH_SEGMENT_H
  11
  12 #include <__cxx03/__config>
  13 #include <__cxx03/__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 // __for_each_segment is a utility function for optimizing iterating over segmented iterators linearly.
  22 // __first and __last are expected to be a segmented range. __func is expected to take a range of local iterators.
  23 // Anything that is returned from __func is ignored.
  24
  25 template <class _SegmentedIterator, class _Functor>
  26 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
  27 __for_each_segment(_SegmentedIterator __first, _SegmentedIterator __last, _Functor __func) {
  28   using _Traits = __segmented_iterator_traits<_SegmentedIterator>;
  29
  30   auto __sfirst = _Traits::__segment(__first);
  31   auto __slast  = _Traits::__segment(__last);
  32
  33   // We are in a single segment, so we might not be at the beginning or end
  34   if (__sfirst == __slast) {
  35     __func(_Traits::__local(__first), _Traits::__local(__last));
  36     return;
  37   }
  38
  39   // We have more than one segment. Iterate over the first segment, since we might not start at the beginning
  40   __func(_Traits::__local(__first), _Traits::__end(__sfirst));
  41   ++__sfirst;
  42   // iterate over the segments which are guaranteed to be completely in the range
  43   while (__sfirst != __slast) {
  44     __func(_Traits::__begin(__sfirst), _Traits::__end(__sfirst));
  45     ++__sfirst;
  46   }
  47   // iterate over the last segment
  48   __func(_Traits::__begin(__sfirst), _Traits::__local(__last));
  49 }
  50
  51 _LIBCPP_END_NAMESPACE_STD
  52
  53 #endif // _LIBCPP___ALGORITHM_FOR_EACH_SEGMENT_H