libcxx/include/__algorithm/search_n.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// 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_SEARCH_N_H
#define _LIBCPP___ALGORITHM_SEARCH_N_H

#include <__config>
#include <__algorithm/comp.h>
#include <__iterator/iterator_traits.h>
#include <type_traits>  // __convert_to_integral

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _BinaryPredicate, class _ForwardIterator, class _Size, class _Tp>
_LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator __search_n(_ForwardIterator __first, _ForwardIterator __last,
                                                          _Size __count, const _Tp& __value_, _BinaryPredicate __pred,
                                                          forward_iterator_tag) {
  if (__count <= 0)
    return __first;
  while (true) {
    // Find first element in sequence that matchs __value_, with a mininum of loop checks
    while (true) {
      if (__first == __last) // return __last if no element matches __value_
        return __last;
      if (__pred(*__first, __value_))
        break;
      ++__first;
    }
    // *__first matches __value_, now match elements after here
    _ForwardIterator __m = __first;
    _Size __c(0);
    while (true) {
      if (++__c == __count) // If pattern exhausted, __first is the answer (works for 1 element pattern)
        return __first;
      if (++__m == __last) // Otherwise if source exhaused, pattern not found
        return __last;
      if (!__pred(*__m, __value_)) // if there is a mismatch, restart with a new __first
      {
        __first = __m;
        ++__first;
        break;
      } // else there is a match, check next elements
    }
  }
}

template <class _BinaryPredicate, class _RandomAccessIterator, class _Size, class _Tp>
_LIBCPP_CONSTEXPR_AFTER_CXX17 _RandomAccessIterator __search_n(_RandomAccessIterator __first,
                                                               _RandomAccessIterator __last, _Size __count,
                                                               const _Tp& __value_, _BinaryPredicate __pred,
                                                               random_access_iterator_tag) {
  typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
  if (__count <= 0)
    return __first;
  _Size __len = static_cast<_Size>(__last - __first);
  if (__len < __count)
    return __last;
  const _RandomAccessIterator __s = __last - difference_type(__count - 1); // Start of pattern match can't go beyond here
  while (true) {
    // Find first element in sequence that matchs __value_, with a mininum of loop checks
    while (true) {
      if (__first >= __s) // return __last if no element matches __value_
        return __last;
      if (__pred(*__first, __value_))
        break;
      ++__first;
    }
    // *__first matches __value_, now match elements after here
    _RandomAccessIterator __m = __first;
    _Size __c(0);
    while (true) {
      if (++__c == __count) // If pattern exhausted, __first is the answer (works for 1 element pattern)
        return __first;
      ++__m;                       // no need to check range on __m because __s guarantees we have enough source
      if (!__pred(*__m, __value_)) // if there is a mismatch, restart with a new __first
      {
        __first = __m;
        ++__first;
        break;
      } // else there is a match, check next elements
    }
  }
}

template <class _ForwardIterator, class _Size, class _Tp, class _BinaryPredicate>
_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator search_n(
    _ForwardIterator __first, _ForwardIterator __last, _Size __count, const _Tp& __value_, _BinaryPredicate __pred) {
  return _VSTD::__search_n<_BinaryPredicate&>(
      __first, __last, _VSTD::__convert_to_integral(__count), __value_, __pred,
      typename iterator_traits<_ForwardIterator>::iterator_category());
}

template <class _ForwardIterator, class _Size, class _Tp>
_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
search_n(_ForwardIterator __first, _ForwardIterator __last, _Size __count, const _Tp& __value_) {
  typedef typename iterator_traits<_ForwardIterator>::value_type __v;
  return _VSTD::search_n(__first, __last, _VSTD::__convert_to_integral(__count), __value_, __equal_to<__v, _Tp>());
}

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___ALGORITHM_SEARCH_N_H