libstdc++-v3/include/bits/stl_iterator_base_funcs.h

// Functions used by iterators -*- C++ -*-

// Copyright (C) 2001-2025 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

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// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
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/*
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1996-1998
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/** @file bits/stl_iterator_base_funcs.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{iterator}
 *
 *  This file contains all of the general iterator-related utility
 *  functions, such as distance() and advance().
 */

#ifndef _STL_ITERATOR_BASE_FUNCS_H
#define _STL_ITERATOR_BASE_FUNCS_H 1

#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif

#include <bits/concept_check.h>
#include <debug/assertions.h>
#include <bits/stl_iterator_base_types.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

_GLIBCXX_BEGIN_NAMESPACE_CONTAINER
  // Forward declaration for the overloads of __distance.
  template <typename> struct _List_iterator;
  template <typename> struct _List_const_iterator;
_GLIBCXX_END_NAMESPACE_CONTAINER

  template<typename _InputIterator>
    inline _GLIBCXX14_CONSTEXPR
    typename iterator_traits<_InputIterator>::difference_type
    __distance(_InputIterator __first, _InputIterator __last,
               input_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)

      typename iterator_traits<_InputIterator>::difference_type __n = 0;
      while (__first != __last)
	{
	  ++__first;
	  ++__n;
	}
      return __n;
    }

  template<typename _RandomAccessIterator>
    __attribute__((__always_inline__))
    inline _GLIBCXX14_CONSTEXPR
    typename iterator_traits<_RandomAccessIterator>::difference_type
    __distance(_RandomAccessIterator __first, _RandomAccessIterator __last,
               random_access_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_RandomAccessIteratorConcept<
				  _RandomAccessIterator>)
      return __last - __first;
    }

#if _GLIBCXX_USE_CXX11_ABI
  // Forward declaration because of the qualified call in distance.
  template<typename _Tp>
    ptrdiff_t
    __distance(_GLIBCXX_STD_C::_List_iterator<_Tp>,
	       _GLIBCXX_STD_C::_List_iterator<_Tp>,
	       input_iterator_tag);

  template<typename _Tp>
    ptrdiff_t
    __distance(_GLIBCXX_STD_C::_List_const_iterator<_Tp>,
	       _GLIBCXX_STD_C::_List_const_iterator<_Tp>,
	       input_iterator_tag);
#endif

#if __cplusplus >= 201103L
  // Give better error if std::distance called with a non-Cpp17InputIterator.
  template<typename _OutputIterator>
    void
    __distance(_OutputIterator, _OutputIterator, output_iterator_tag) = delete;
#endif

  /**
   *  @brief A generalization of pointer arithmetic.
   *  @param  __first  An input iterator.
   *  @param  __last  An input iterator.
   *  @return  The distance between them.
   *
   *  Returns @c n such that __first + n == __last.  This requires
   *  that @p __last must be reachable from @p __first.  Note that @c
   *  n may be negative.
   *
   *  For random access iterators, this uses their @c + and @c - operations
   *  and are constant time.  For other %iterator classes they are linear time.
  */
  template<typename _InputIterator>
    _GLIBCXX_NODISCARD __attribute__((__always_inline__))
    inline _GLIBCXX17_CONSTEXPR
    typename iterator_traits<_InputIterator>::difference_type
    distance(_InputIterator __first, _InputIterator __last)
    {
      // concept requirements -- taken care of in __distance
      return std::__distance(__first, __last,
			     std::__iterator_category(__first));
    }

  template<typename _InputIterator, typename _Distance>
    inline _GLIBCXX14_CONSTEXPR void
    __advance(_InputIterator& __i, _Distance __n, input_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_assert(__n >= 0);
      while (__n--)
	++__i;
    }

  template<typename _BidirectionalIterator, typename _Distance>
    inline _GLIBCXX14_CONSTEXPR void
    __advance(_BidirectionalIterator& __i, _Distance __n,
	      bidirectional_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator>)
      if (__n > 0)
        while (__n--)
	  ++__i;
      else
        while (__n++)
	  --__i;
    }

  template<typename _RandomAccessIterator, typename _Distance>
    inline _GLIBCXX14_CONSTEXPR void
    __advance(_RandomAccessIterator& __i, _Distance __n,
              random_access_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_RandomAccessIteratorConcept<
				  _RandomAccessIterator>)
      if (__builtin_constant_p(__n) && __n == 1)
	++__i;
      else if (__builtin_constant_p(__n) && __n == -1)
	--__i;
      else
	__i += __n;
    }

#if __cplusplus >= 201103L
  // Give better error if std::advance called with a non-Cpp17InputIterator.
  template<typename _OutputIterator, typename _Distance>
    void
    __advance(_OutputIterator&, _Distance, output_iterator_tag) = delete;
#endif

  /**
   *  @brief A generalization of pointer arithmetic.
   *  @param  __i  An input iterator.
   *  @param  __n  The @a delta by which to change @p __i.
   *  @return  Nothing.
   *
   *  This increments @p i by @p n.  For bidirectional and random access
   *  iterators, @p __n may be negative, in which case @p __i is decremented.
   *
   *  For random access iterators, this uses their @c + and @c - operations
   *  and are constant time.  For other %iterator classes they are linear time.
  */
  template<typename _InputIterator, typename _Distance>
    __attribute__((__always_inline__))
    inline _GLIBCXX17_CONSTEXPR void
    advance(_InputIterator& __i, _Distance __n)
    {
      // concept requirements -- taken care of in __advance
      typename iterator_traits<_InputIterator>::difference_type __d = __n;
      std::__advance(__i, __d, std::__iterator_category(__i));
    }

#if __cplusplus >= 201103L

  template<typename _InputIterator>
    _GLIBCXX_NODISCARD [[__gnu__::__always_inline__]]
    inline _GLIBCXX17_CONSTEXPR _InputIterator
    next(_InputIterator __x, typename
	 iterator_traits<_InputIterator>::difference_type __n = 1)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      std::advance(__x, __n);
      return __x;
    }

  template<typename _BidirectionalIterator>
    _GLIBCXX_NODISCARD [[__gnu__::__always_inline__]]
    inline _GLIBCXX17_CONSTEXPR _BidirectionalIterator
    prev(_BidirectionalIterator __x, typename
	 iterator_traits<_BidirectionalIterator>::difference_type __n = 1)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator>)
      std::advance(__x, -__n);
      return __x;
    }

#endif // C++11

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif /* _STL_ITERATOR_BASE_FUNCS_H */