// Core algorithmic facilities -*- C++ -*-

// Copyright (C) 2001-2016 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.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// 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
// <http://www.gnu.org/licenses/>.

/*
 *
 * 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_algobase.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{algorithm}
 */

#ifndef _STL_ALGOBASE_H
#define _STL_ALGOBASE_H 1

#include <bits/c++config.h>
#include <bits/functexcept.h>
#include <bits/cpp_type_traits.h>
#include <ext/type_traits.h>
#include <ext/numeric_traits.h>
#include <bits/stl_pair.h>
#include <bits/stl_iterator_base_types.h>
#include <bits/stl_iterator_base_funcs.h>
#include <bits/stl_iterator.h>
#include <bits/concept_check.h>
#include <debug/debug.h>
#include <bits/move.h> // For std::swap and _GLIBCXX_MOVE
#include <bits/predefined_ops.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

#if __cplusplus < 201103L
  // See http://gcc.gnu.org/ml/libstdc++/2004-08/msg00167.html: in a
  // nutshell, we are partially implementing the resolution of DR 187,
  // when it's safe, i.e., the value_types are equal.
  template<bool _BoolType>
    struct __iter_swap
    {
      template<typename _ForwardIterator1, typename _ForwardIterator2>
        static void
        iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
        {
          typedef typename iterator_traits<_ForwardIterator1>::value_type
            _ValueType1;
          _ValueType1 __tmp = _GLIBCXX_MOVE(*__a);
          *__a = _GLIBCXX_MOVE(*__b);
          *__b = _GLIBCXX_MOVE(__tmp);
	}
    };

  template<>
    struct __iter_swap<true>
    {
      template<typename _ForwardIterator1, typename _ForwardIterator2>
        static void 
        iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
        {
          swap(*__a, *__b);
        }
    };
#endif

  /**
   *  @brief Swaps the contents of two iterators.
   *  @ingroup mutating_algorithms
   *  @param  __a  An iterator.
   *  @param  __b  Another iterator.
   *  @return   Nothing.
   *
   *  This function swaps the values pointed to by two iterators, not the
   *  iterators themselves.
  */
  template<typename _ForwardIterator1, typename _ForwardIterator2>
    inline void
    iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator1>)
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator2>)

#if __cplusplus < 201103L
      typedef typename iterator_traits<_ForwardIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_ForwardIterator2>::value_type
	_ValueType2;

      __glibcxx_function_requires(_ConvertibleConcept<_ValueType1,
				  _ValueType2>)
      __glibcxx_function_requires(_ConvertibleConcept<_ValueType2,
				  _ValueType1>)

      typedef typename iterator_traits<_ForwardIterator1>::reference
	_ReferenceType1;
      typedef typename iterator_traits<_ForwardIterator2>::reference
	_ReferenceType2;
      std::__iter_swap<__are_same<_ValueType1, _ValueType2>::__value
	&& __are_same<_ValueType1&, _ReferenceType1>::__value
	&& __are_same<_ValueType2&, _ReferenceType2>::__value>::
	iter_swap(__a, __b);
#else
      swap(*__a, *__b);
#endif
    }

  /**
   *  @brief Swap the elements of two sequences.
   *  @ingroup mutating_algorithms
   *  @param  __first1  A forward iterator.
   *  @param  __last1   A forward iterator.
   *  @param  __first2  A forward iterator.
   *  @return   An iterator equal to @p first2+(last1-first1).
   *
   *  Swaps each element in the range @p [first1,last1) with the
   *  corresponding element in the range @p [first2,(last1-first1)).
   *  The ranges must not overlap.
  */
  template<typename _ForwardIterator1, typename _ForwardIterator2>
    _ForwardIterator2
    swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
		_ForwardIterator2 __first2)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator1>)
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator2>)
      __glibcxx_requires_valid_range(__first1, __last1);

      for (; __first1 != __last1; ++__first1, (void)++__first2)
	std::iter_swap(__first1, __first2);
      return __first2;
    }

  /**
   *  @brief This does what you think it does.
   *  @ingroup sorting_algorithms
   *  @param  __a  A thing of arbitrary type.
   *  @param  __b  Another thing of arbitrary type.
   *  @return   The lesser of the parameters.
   *
   *  This is the simple classic generic implementation.  It will work on
   *  temporary expressions, since they are only evaluated once, unlike a
   *  preprocessor macro.
  */
  template<typename _Tp>
    _GLIBCXX14_CONSTEXPR
    inline const _Tp&
    min(const _Tp& __a, const _Tp& __b)
    {
      // concept requirements
      __glibcxx_function_requires(_LessThanComparableConcept<_Tp>)
      //return __b < __a ? __b : __a;
      if (__b < __a)
	return __b;
      return __a;
    }

  /**
   *  @brief This does what you think it does.
   *  @ingroup sorting_algorithms
   *  @param  __a  A thing of arbitrary type.
   *  @param  __b  Another thing of arbitrary type.
   *  @return   The greater of the parameters.
   *
   *  This is the simple classic generic implementation.  It will work on
   *  temporary expressions, since they are only evaluated once, unlike a
   *  preprocessor macro.
  */
  template<typename _Tp>
    _GLIBCXX14_CONSTEXPR
    inline const _Tp&
    max(const _Tp& __a, const _Tp& __b)
    {
      // concept requirements
      __glibcxx_function_requires(_LessThanComparableConcept<_Tp>)
      //return  __a < __b ? __b : __a;
      if (__a < __b)
	return __b;
      return __a;
    }

  /**
   *  @brief This does what you think it does.
   *  @ingroup sorting_algorithms
   *  @param  __a  A thing of arbitrary type.
   *  @param  __b  Another thing of arbitrary type.
   *  @param  __comp  A @link comparison_functors comparison functor@endlink.
   *  @return   The lesser of the parameters.
   *
   *  This will work on temporary expressions, since they are only evaluated
   *  once, unlike a preprocessor macro.
  */
  template<typename _Tp, typename _Compare>
    _GLIBCXX14_CONSTEXPR
    inline const _Tp&
    min(const _Tp& __a, const _Tp& __b, _Compare __comp)
    {
      //return __comp(__b, __a) ? __b : __a;
      if (__comp(__b, __a))
	return __b;
      return __a;
    }

  /**
   *  @brief This does what you think it does.
   *  @ingroup sorting_algorithms
   *  @param  __a  A thing of arbitrary type.
   *  @param  __b  Another thing of arbitrary type.
   *  @param  __comp  A @link comparison_functors comparison functor@endlink.
   *  @return   The greater of the parameters.
   *
   *  This will work on temporary expressions, since they are only evaluated
   *  once, unlike a preprocessor macro.
  */
  template<typename _Tp, typename _Compare>
    _GLIBCXX14_CONSTEXPR
    inline const _Tp&
    max(const _Tp& __a, const _Tp& __b, _Compare __comp)
    {
      //return __comp(__a, __b) ? __b : __a;
      if (__comp(__a, __b))
	return __b;
      return __a;
    }

  // Fallback implementation of the function in bits/stl_iterator.h used to
  // remove the __normal_iterator wrapper. See copy, fill, ...
  template<typename _Iterator>
    inline _Iterator
    __niter_base(_Iterator __it)
    { return __it; }

  // All of these auxiliary structs serve two purposes.  (1) Replace
  // calls to copy with memmove whenever possible.  (Memmove, not memcpy,
  // because the input and output ranges are permitted to overlap.)
  // (2) If we're using random access iterators, then write the loop as
  // a for loop with an explicit count.

  template<bool, bool, typename>
    struct __copy_move
    {
      template<typename _II, typename _OI>
        static _OI
        __copy_m(_II __first, _II __last, _OI __result)
        {
	  for (; __first != __last; ++__result, (void)++__first)
	    *__result = *__first;
	  return __result;
	}
    };

#if __cplusplus >= 201103L
  template<typename _Category>
    struct __copy_move<true, false, _Category>
    {
      template<typename _II, typename _OI>
        static _OI
        __copy_m(_II __first, _II __last, _OI __result)
        {
	  for (; __first != __last; ++__result, (void)++__first)
	    *__result = std::move(*__first);
	  return __result;
	}
    };
#endif

  template<>
    struct __copy_move<false, false, random_access_iterator_tag>
    {
      template<typename _II, typename _OI>
        static _OI
        __copy_m(_II __first, _II __last, _OI __result)
        { 
	  typedef typename iterator_traits<_II>::difference_type _Distance;
	  for(_Distance __n = __last - __first; __n > 0; --__n)
	    {
	      *__result = *__first;
	      ++__first;
	      ++__result;
	    }
	  return __result;
	}
    };

#if __cplusplus >= 201103L
  template<>
    struct __copy_move<true, false, random_access_iterator_tag>
    {
      template<typename _II, typename _OI>
        static _OI
        __copy_m(_II __first, _II __last, _OI __result)
        { 
	  typedef typename iterator_traits<_II>::difference_type _Distance;
	  for(_Distance __n = __last - __first; __n > 0; --__n)
	    {
	      *__result = std::move(*__first);
	      ++__first;
	      ++__result;
	    }
	  return __result;
	}
    };
#endif

  template<bool _IsMove>
    struct __copy_move<_IsMove, true, random_access_iterator_tag>
    {
      template<typename _Tp>
        static _Tp*
        __copy_m(const _Tp* __first, const _Tp* __last, _Tp* __result)
        {
#if __cplusplus >= 201103L
	  using __assignable = conditional<_IsMove,
					   is_move_assignable<_Tp>,
					   is_copy_assignable<_Tp>>;
	  // trivial types can have deleted assignment
	  static_assert( __assignable::type::value, "type is not assignable" );
#endif
	  const ptrdiff_t _Num = __last - __first;
	  if (_Num)
	    __builtin_memmove(__result, __first, sizeof(_Tp) * _Num);
	  return __result + _Num;
	}
    };

  template<bool _IsMove, typename _II, typename _OI>
    inline _OI
    __copy_move_a(_II __first, _II __last, _OI __result)
    {
      typedef typename iterator_traits<_II>::value_type _ValueTypeI;
      typedef typename iterator_traits<_OI>::value_type _ValueTypeO;
      typedef typename iterator_traits<_II>::iterator_category _Category;
      const bool __simple = (__is_trivial(_ValueTypeI)
	                     && __is_pointer<_II>::__value
	                     && __is_pointer<_OI>::__value
			     && __are_same<_ValueTypeI, _ValueTypeO>::__value);

      return std::__copy_move<_IsMove, __simple,
	                      _Category>::__copy_m(__first, __last, __result);
    }

  // Helpers for streambuf iterators (either istream or ostream).
  // NB: avoid including <iosfwd>, relatively large.
  template<typename _CharT>
    struct char_traits;

  template<typename _CharT, typename _Traits>
    class istreambuf_iterator;

  template<typename _CharT, typename _Traits>
    class ostreambuf_iterator;

  template<bool _IsMove, typename _CharT>
    typename __gnu_cxx::__enable_if<__is_char<_CharT>::__value, 
	     ostreambuf_iterator<_CharT, char_traits<_CharT> > >::__type
    __copy_move_a2(_CharT*, _CharT*,
		   ostreambuf_iterator<_CharT, char_traits<_CharT> >);

  template<bool _IsMove, typename _CharT>
    typename __gnu_cxx::__enable_if<__is_char<_CharT>::__value, 
	     ostreambuf_iterator<_CharT, char_traits<_CharT> > >::__type
    __copy_move_a2(const _CharT*, const _CharT*,
		   ostreambuf_iterator<_CharT, char_traits<_CharT> >);

  template<bool _IsMove, typename _CharT>
    typename __gnu_cxx::__enable_if<__is_char<_CharT>::__value,
				    _CharT*>::__type
    __copy_move_a2(istreambuf_iterator<_CharT, char_traits<_CharT> >,
		   istreambuf_iterator<_CharT, char_traits<_CharT> >, _CharT*);

  template<bool _IsMove, typename _II, typename _OI>
    inline _OI
    __copy_move_a2(_II __first, _II __last, _OI __result)
    {
      return _OI(std::__copy_move_a<_IsMove>(std::__niter_base(__first),
					     std::__niter_base(__last),
					     std::__niter_base(__result)));
    }

  /**
   *  @brief Copies the range [first,last) into result.
   *  @ingroup mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __result An output iterator.
   *  @return   result + (first - last)
   *
   *  This inline function will boil down to a call to @c memmove whenever
   *  possible.  Failing that, if random access iterators are passed, then the
   *  loop count will be known (and therefore a candidate for compiler
   *  optimizations such as unrolling).  Result may not be contained within
   *  [first,last); the copy_backward function should be used instead.
   *
   *  Note that the end of the output range is permitted to be contained
   *  within [first,last).
  */
  template<typename _II, typename _OI>
    inline _OI
    copy(_II __first, _II __last, _OI __result)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_II>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OI,
	    typename iterator_traits<_II>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      return (std::__copy_move_a2<__is_move_iterator<_II>::__value>
	      (std::__miter_base(__first), std::__miter_base(__last),
	       __result));
    }

#if __cplusplus >= 201103L
  /**
   *  @brief Moves the range [first,last) into result.
   *  @ingroup mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __result An output iterator.
   *  @return   result + (first - last)
   *
   *  This inline function will boil down to a call to @c memmove whenever
   *  possible.  Failing that, if random access iterators are passed, then the
   *  loop count will be known (and therefore a candidate for compiler
   *  optimizations such as unrolling).  Result may not be contained within
   *  [first,last); the move_backward function should be used instead.
   *
   *  Note that the end of the output range is permitted to be contained
   *  within [first,last).
  */
  template<typename _II, typename _OI>
    inline _OI
    move(_II __first, _II __last, _OI __result)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_II>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OI,
	    typename iterator_traits<_II>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      return std::__copy_move_a2<true>(std::__miter_base(__first),
				       std::__miter_base(__last), __result);
    }

#define _GLIBCXX_MOVE3(_Tp, _Up, _Vp) std::move(_Tp, _Up, _Vp)
#else
#define _GLIBCXX_MOVE3(_Tp, _Up, _Vp) std::copy(_Tp, _Up, _Vp)
#endif

  template<bool, bool, typename>
    struct __copy_move_backward
    {
      template<typename _BI1, typename _BI2>
        static _BI2
        __copy_move_b(_BI1 __first, _BI1 __last, _BI2 __result)
        {
	  while (__first != __last)
	    *--__result = *--__last;
	  return __result;
	}
    };

#if __cplusplus >= 201103L
  template<typename _Category>
    struct __copy_move_backward<true, false, _Category>
    {
      template<typename _BI1, typename _BI2>
        static _BI2
        __copy_move_b(_BI1 __first, _BI1 __last, _BI2 __result)
        {
	  while (__first != __last)
	    *--__result = std::move(*--__last);
	  return __result;
	}
    };
#endif

  template<>
    struct __copy_move_backward<false, false, random_access_iterator_tag>
    {
      template<typename _BI1, typename _BI2>
        static _BI2
        __copy_move_b(_BI1 __first, _BI1 __last, _BI2 __result)
        {
	  typename iterator_traits<_BI1>::difference_type __n;
	  for (__n = __last - __first; __n > 0; --__n)
	    *--__result = *--__last;
	  return __result;
	}
    };

#if __cplusplus >= 201103L
  template<>
    struct __copy_move_backward<true, false, random_access_iterator_tag>
    {
      template<typename _BI1, typename _BI2>
        static _BI2
        __copy_move_b(_BI1 __first, _BI1 __last, _BI2 __result)
        {
	  typename iterator_traits<_BI1>::difference_type __n;
	  for (__n = __last - __first; __n > 0; --__n)
	    *--__result = std::move(*--__last);
	  return __result;
	}
    };
#endif

  template<bool _IsMove>
    struct __copy_move_backward<_IsMove, true, random_access_iterator_tag>
    {
      template<typename _Tp>
        static _Tp*
        __copy_move_b(const _Tp* __first, const _Tp* __last, _Tp* __result)
        {
#if __cplusplus >= 201103L
	  using __assignable = conditional<_IsMove,
					   is_move_assignable<_Tp>,
					   is_copy_assignable<_Tp>>;
	  // trivial types can have deleted assignment
	  static_assert( __assignable::type::value, "type is not assignable" );
#endif
	  const ptrdiff_t _Num = __last - __first;
	  if (_Num)
	    __builtin_memmove(__result - _Num, __first, sizeof(_Tp) * _Num);
	  return __result - _Num;
	}
    };

  template<bool _IsMove, typename _BI1, typename _BI2>
    inline _BI2
    __copy_move_backward_a(_BI1 __first, _BI1 __last, _BI2 __result)
    {
      typedef typename iterator_traits<_BI1>::value_type _ValueType1;
      typedef typename iterator_traits<_BI2>::value_type _ValueType2;
      typedef typename iterator_traits<_BI1>::iterator_category _Category;
      const bool __simple = (__is_trivial(_ValueType1)
	                     && __is_pointer<_BI1>::__value
	                     && __is_pointer<_BI2>::__value
			     && __are_same<_ValueType1, _ValueType2>::__value);

      return std::__copy_move_backward<_IsMove, __simple,
	                               _Category>::__copy_move_b(__first,
								 __last,
								 __result);
    }

  template<bool _IsMove, typename _BI1, typename _BI2>
    inline _BI2
    __copy_move_backward_a2(_BI1 __first, _BI1 __last, _BI2 __result)
    {
      return _BI2(std::__copy_move_backward_a<_IsMove>
		  (std::__niter_base(__first), std::__niter_base(__last),
		   std::__niter_base(__result)));
    }

  /**
   *  @brief Copies the range [first,last) into result.
   *  @ingroup mutating_algorithms
   *  @param  __first  A bidirectional iterator.
   *  @param  __last   A bidirectional iterator.
   *  @param  __result A bidirectional iterator.
   *  @return   result - (first - last)
   *
   *  The function has the same effect as copy, but starts at the end of the
   *  range and works its way to the start, returning the start of the result.
   *  This inline function will boil down to a call to @c memmove whenever
   *  possible.  Failing that, if random access iterators are passed, then the
   *  loop count will be known (and therefore a candidate for compiler
   *  optimizations such as unrolling).
   *
   *  Result may not be in the range (first,last].  Use copy instead.  Note
   *  that the start of the output range may overlap [first,last).
  */
  template<typename _BI1, typename _BI2>
    inline _BI2
    copy_backward(_BI1 __first, _BI1 __last, _BI2 __result)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<_BI1>)
      __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<_BI2>)
      __glibcxx_function_requires(_ConvertibleConcept<
	    typename iterator_traits<_BI1>::value_type,
	    typename iterator_traits<_BI2>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      return (std::__copy_move_backward_a2<__is_move_iterator<_BI1>::__value>
	      (std::__miter_base(__first), std::__miter_base(__last),
	       __result));
    }

#if __cplusplus >= 201103L
  /**
   *  @brief Moves the range [first,last) into result.
   *  @ingroup mutating_algorithms
   *  @param  __first  A bidirectional iterator.
   *  @param  __last   A bidirectional iterator.
   *  @param  __result A bidirectional iterator.
   *  @return   result - (first - last)
   *
   *  The function has the same effect as move, but starts at the end of the
   *  range and works its way to the start, returning the start of the result.
   *  This inline function will boil down to a call to @c memmove whenever
   *  possible.  Failing that, if random access iterators are passed, then the
   *  loop count will be known (and therefore a candidate for compiler
   *  optimizations such as unrolling).
   *
   *  Result may not be in the range (first,last].  Use move instead.  Note
   *  that the start of the output range may overlap [first,last).
  */
  template<typename _BI1, typename _BI2>
    inline _BI2
    move_backward(_BI1 __first, _BI1 __last, _BI2 __result)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<_BI1>)
      __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<_BI2>)
      __glibcxx_function_requires(_ConvertibleConcept<
	    typename iterator_traits<_BI1>::value_type,
	    typename iterator_traits<_BI2>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      return std::__copy_move_backward_a2<true>(std::__miter_base(__first),
						std::__miter_base(__last),
						__result);
    }

#define _GLIBCXX_MOVE_BACKWARD3(_Tp, _Up, _Vp) std::move_backward(_Tp, _Up, _Vp)
#else
#define _GLIBCXX_MOVE_BACKWARD3(_Tp, _Up, _Vp) std::copy_backward(_Tp, _Up, _Vp)
#endif

  template<typename _ForwardIterator, typename _Tp>
    inline typename
    __gnu_cxx::__enable_if<!__is_scalar<_Tp>::__value, void>::__type
    __fill_a(_ForwardIterator __first, _ForwardIterator __last,
 	     const _Tp& __value)
    {
      for (; __first != __last; ++__first)
	*__first = __value;
    }
    
  template<typename _ForwardIterator, typename _Tp>
    inline typename
    __gnu_cxx::__enable_if<__is_scalar<_Tp>::__value, void>::__type
    __fill_a(_ForwardIterator __first, _ForwardIterator __last,
	     const _Tp& __value)
    {
      const _Tp __tmp = __value;
      for (; __first != __last; ++__first)
	*__first = __tmp;
    }

  // Specialization: for char types we can use memset.
  template<typename _Tp>
    inline typename
    __gnu_cxx::__enable_if<__is_byte<_Tp>::__value, void>::__type
    __fill_a(_Tp* __first, _Tp* __last, const _Tp& __c)
    {
      const _Tp __tmp = __c;
      if (const size_t __len = __last - __first)
	__builtin_memset(__first, static_cast<unsigned char>(__tmp), __len);
    }

  /**
   *  @brief Fills the range [first,last) with copies of value.
   *  @ingroup mutating_algorithms
   *  @param  __first  A forward iterator.
   *  @param  __last   A forward iterator.
   *  @param  __value  A reference-to-const of arbitrary type.
   *  @return   Nothing.
   *
   *  This function fills a range with copies of the same value.  For char
   *  types filling contiguous areas of memory, this becomes an inline call
   *  to @c memset or @c wmemset.
  */
  template<typename _ForwardIterator, typename _Tp>
    inline void
    fill(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator>)
      __glibcxx_requires_valid_range(__first, __last);

      std::__fill_a(std::__niter_base(__first), std::__niter_base(__last),
		    __value);
    }

  template<typename _OutputIterator, typename _Size, typename _Tp>
    inline typename
    __gnu_cxx::__enable_if<!__is_scalar<_Tp>::__value, _OutputIterator>::__type
    __fill_n_a(_OutputIterator __first, _Size __n, const _Tp& __value)
    {
      for (__decltype(__n + 0) __niter = __n;
	   __niter > 0; --__niter, ++__first)
	*__first = __value;
      return __first;
    }

  template<typename _OutputIterator, typename _Size, typename _Tp>
    inline typename
    __gnu_cxx::__enable_if<__is_scalar<_Tp>::__value, _OutputIterator>::__type
    __fill_n_a(_OutputIterator __first, _Size __n, const _Tp& __value)
    {
      const _Tp __tmp = __value;
      for (__decltype(__n + 0) __niter = __n;
	   __niter > 0; --__niter, ++__first)
	*__first = __tmp;
      return __first;
    }

  template<typename _Size, typename _Tp>
    inline typename
    __gnu_cxx::__enable_if<__is_byte<_Tp>::__value, _Tp*>::__type
    __fill_n_a(_Tp* __first, _Size __n, const _Tp& __c)
    {
      std::__fill_a(__first, __first + __n, __c);
      return __first + __n;
    }

  /**
   *  @brief Fills the range [first,first+n) with copies of value.
   *  @ingroup mutating_algorithms
   *  @param  __first  An output iterator.
   *  @param  __n      The count of copies to perform.
   *  @param  __value  A reference-to-const of arbitrary type.
   *  @return   The iterator at first+n.
   *
   *  This function fills a range with copies of the same value.  For char
   *  types filling contiguous areas of memory, this becomes an inline call
   *  to @c memset or @ wmemset.
   *
   *  _GLIBCXX_RESOLVE_LIB_DEFECTS
   *  DR 865. More algorithms that throw away information
  */
  template<typename _OI, typename _Size, typename _Tp>
    inline _OI
    fill_n(_OI __first, _Size __n, const _Tp& __value)
    {
      // concept requirements
      __glibcxx_function_requires(_OutputIteratorConcept<_OI, _Tp>)

      return _OI(std::__fill_n_a(std::__niter_base(__first), __n, __value));
    }

  template<bool _BoolType>
    struct __equal
    {
      template<typename _II1, typename _II2>
        static bool
        equal(_II1 __first1, _II1 __last1, _II2 __first2)
        {
	  for (; __first1 != __last1; ++__first1, (void)++__first2)
	    if (!(*__first1 == *__first2))
	      return false;
	  return true;
	}
    };

  template<>
    struct __equal<true>
    {
      template<typename _Tp>
        static bool
        equal(const _Tp* __first1, const _Tp* __last1, const _Tp* __first2)
        {
	  if (const size_t __len = (__last1 - __first1))
	    return !__builtin_memcmp(__first1, __first2, sizeof(_Tp) * __len);
	  return true;
	}
    };

  template<typename _II1, typename _II2>
    inline bool
    __equal_aux(_II1 __first1, _II1 __last1, _II2 __first2)
    {
      typedef typename iterator_traits<_II1>::value_type _ValueType1;
      typedef typename iterator_traits<_II2>::value_type _ValueType2;
      const bool __simple = ((__is_integer<_ValueType1>::__value
			      || __is_pointer<_ValueType1>::__value)
	                     && __is_pointer<_II1>::__value
	                     && __is_pointer<_II2>::__value
			     && __are_same<_ValueType1, _ValueType2>::__value);

      return std::__equal<__simple>::equal(__first1, __last1, __first2);
    }

  template<typename, typename>
    struct __lc_rai
    {
      template<typename _II1, typename _II2>
        static _II1
        __newlast1(_II1, _II1 __last1, _II2, _II2)
        { return __last1; }

      template<typename _II>
        static bool
        __cnd2(_II __first, _II __last)
        { return __first != __last; }
    };

  template<>
    struct __lc_rai<random_access_iterator_tag, random_access_iterator_tag>
    {
      template<typename _RAI1, typename _RAI2>
        static _RAI1
        __newlast1(_RAI1 __first1, _RAI1 __last1,
		   _RAI2 __first2, _RAI2 __last2)
        {
	  const typename iterator_traits<_RAI1>::difference_type
	    __diff1 = __last1 - __first1;
	  const typename iterator_traits<_RAI2>::difference_type
	    __diff2 = __last2 - __first2;
	  return __diff2 < __diff1 ? __first1 + __diff2 : __last1;
	}

      template<typename _RAI>
        static bool
        __cnd2(_RAI, _RAI)
        { return true; }
    };

  template<typename _II1, typename _II2, typename _Compare>
    bool
    __lexicographical_compare_impl(_II1 __first1, _II1 __last1,
				   _II2 __first2, _II2 __last2,
				   _Compare __comp)
    {
      typedef typename iterator_traits<_II1>::iterator_category _Category1;
      typedef typename iterator_traits<_II2>::iterator_category _Category2;
      typedef std::__lc_rai<_Category1, _Category2> __rai_type;

      __last1 = __rai_type::__newlast1(__first1, __last1, __first2, __last2);
      for (; __first1 != __last1 && __rai_type::__cnd2(__first2, __last2);
	   ++__first1, (void)++__first2)
	{
	  if (__comp(__first1, __first2))
	    return true;
	  if (__comp(__first2, __first1))
	    return false;
	}
      return __first1 == __last1 && __first2 != __last2;
    }

  template<bool _BoolType>
    struct __lexicographical_compare
    {
      template<typename _II1, typename _II2>
        static bool __lc(_II1, _II1, _II2, _II2);
    };

  template<bool _BoolType>
    template<typename _II1, typename _II2>
      bool
      __lexicographical_compare<_BoolType>::
      __lc(_II1 __first1, _II1 __last1, _II2 __first2, _II2 __last2)
      {
	return std::__lexicographical_compare_impl(__first1, __last1,
						   __first2, __last2,
					__gnu_cxx::__ops::__iter_less_iter());
      }

  template<>
    struct __lexicographical_compare<true>
    {
      template<typename _Tp, typename _Up>
        static bool
        __lc(const _Tp* __first1, const _Tp* __last1,
	     const _Up* __first2, const _Up* __last2)
	{
	  const size_t __len1 = __last1 - __first1;
	  const size_t __len2 = __last2 - __first2;
	  if (const size_t __len = std::min(__len1, __len2))
	    if (int __result = __builtin_memcmp(__first1, __first2, __len))
	      return __result < 0;
	  return __len1 < __len2;
	}
    };

  template<typename _II1, typename _II2>
    inline bool
    __lexicographical_compare_aux(_II1 __first1, _II1 __last1,
				  _II2 __first2, _II2 __last2)
    {
      typedef typename iterator_traits<_II1>::value_type _ValueType1;
      typedef typename iterator_traits<_II2>::value_type _ValueType2;
      const bool __simple =
	(__is_byte<_ValueType1>::__value && __is_byte<_ValueType2>::__value
	 && !__gnu_cxx::__numeric_traits<_ValueType1>::__is_signed
	 && !__gnu_cxx::__numeric_traits<_ValueType2>::__is_signed
	 && __is_pointer<_II1>::__value
	 && __is_pointer<_II2>::__value);

      return std::__lexicographical_compare<__simple>::__lc(__first1, __last1,
							    __first2, __last2);
    }

  template<typename _ForwardIterator, typename _Tp, typename _Compare>
    _ForwardIterator
    __lower_bound(_ForwardIterator __first, _ForwardIterator __last,
		  const _Tp& __val, _Compare __comp)
    {
      typedef typename iterator_traits<_ForwardIterator>::difference_type
	_DistanceType;

      _DistanceType __len = std::distance(__first, __last);

      while (__len > 0)
	{
	  _DistanceType __half = __len >> 1;
	  _ForwardIterator __middle = __first;
	  std::advance(__middle, __half);
	  if (__comp(__middle, __val))
	    {
	      __first = __middle;
	      ++__first;
	      __len = __len - __half - 1;
	    }
	  else
	    __len = __half;
	}
      return __first;
    }

  /**
   *  @brief Finds the first position in which @a val could be inserted
   *         without changing the ordering.
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __val     The search term.
   *  @return         An iterator pointing to the first element <em>not less
   *                  than</em> @a val, or end() if every element is less than 
   *                  @a val.
   *  @ingroup binary_search_algorithms
  */
  template<typename _ForwardIterator, typename _Tp>
    inline _ForwardIterator
    lower_bound(_ForwardIterator __first, _ForwardIterator __last,
		const _Tp& __val)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_LessThanOpConcept<
	    typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
      __glibcxx_requires_partitioned_lower(__first, __last, __val);
      __glibcxx_requires_irreflexive2(__first, __last);

      return std::__lower_bound(__first, __last, __val,
				__gnu_cxx::__ops::__iter_less_val());
    }

  /// This is a helper function for the sort routines and for random.tcc.
  //  Precondition: __n > 0.
  inline _GLIBCXX_CONSTEXPR int
  __lg(int __n)
  { return sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }

  inline _GLIBCXX_CONSTEXPR unsigned
  __lg(unsigned __n)
  { return sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }

  inline _GLIBCXX_CONSTEXPR long
  __lg(long __n)
  { return sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }

  inline _GLIBCXX_CONSTEXPR unsigned long
  __lg(unsigned long __n)
  { return sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }

  inline _GLIBCXX_CONSTEXPR long long
  __lg(long long __n)
  { return sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }

  inline _GLIBCXX_CONSTEXPR unsigned long long
  __lg(unsigned long long __n)
  { return sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }

_GLIBCXX_END_NAMESPACE_VERSION

_GLIBCXX_BEGIN_NAMESPACE_ALGO

  /**
   *  @brief Tests a range for element-wise equality.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @return   A boolean true or false.
   *
   *  This compares the elements of two ranges using @c == and returns true or
   *  false depending on whether all of the corresponding elements of the
   *  ranges are equal.
  */
  template<typename _II1, typename _II2>
    inline bool
    equal(_II1 __first1, _II1 __last1, _II2 __first2)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_II1>)
      __glibcxx_function_requires(_InputIteratorConcept<_II2>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_II1>::value_type,
	    typename iterator_traits<_II2>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);

      return std::__equal_aux(std::__niter_base(__first1),
			      std::__niter_base(__last1),
			      std::__niter_base(__first2));
    }

  /**
   *  @brief Tests a range for element-wise equality.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @param __binary_pred A binary predicate @link functors
   *                  functor@endlink.
   *  @return         A boolean true or false.
   *
   *  This compares the elements of two ranges using the binary_pred
   *  parameter, and returns true or
   *  false depending on whether all of the corresponding elements of the
   *  ranges are equal.
  */
  template<typename _IIter1, typename _IIter2, typename _BinaryPredicate>
    inline bool
    equal(_IIter1 __first1, _IIter1 __last1,
	  _IIter2 __first2, _BinaryPredicate __binary_pred)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_IIter1>)
      __glibcxx_function_requires(_InputIteratorConcept<_IIter2>)
      __glibcxx_requires_valid_range(__first1, __last1);

      for (; __first1 != __last1; ++__first1, (void)++__first2)
	if (!bool(__binary_pred(*__first1, *__first2)))
	  return false;
      return true;
    }

#if __cplusplus > 201103L

#define __cpp_lib_robust_nonmodifying_seq_ops 201304

  /**
   *  @brief Tests a range for element-wise equality.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @param  __last2   An input iterator.
   *  @return   A boolean true or false.
   *
   *  This compares the elements of two ranges using @c == and returns true or
   *  false depending on whether all of the corresponding elements of the
   *  ranges are equal.
  */
  template<typename _II1, typename _II2>
    inline bool
    equal(_II1 __first1, _II1 __last1, _II2 __first2, _II2 __last2)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_II1>)
      __glibcxx_function_requires(_InputIteratorConcept<_II2>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_II1>::value_type,
	    typename iterator_traits<_II2>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      using _RATag = random_access_iterator_tag;
      using _Cat1 = typename iterator_traits<_II1>::iterator_category;
      using _Cat2 = typename iterator_traits<_II2>::iterator_category;
      using _RAIters = __and_<is_same<_Cat1, _RATag>, is_same<_Cat2, _RATag>>;
      if (_RAIters())
	{
	  auto __d1 = std::distance(__first1, __last1);
	  auto __d2 = std::distance(__first2, __last2);
	  if (__d1 != __d2)
	    return false;
	  return _GLIBCXX_STD_A::equal(__first1, __last1, __first2);
	}

      for (; __first1 != __last1 && __first2 != __last2;
	  ++__first1, (void)++__first2)
	if (!(*__first1 == *__first2))
	  return false;
      return __first1 == __last1 && __first2 == __last2;
    }

  /**
   *  @brief Tests a range for element-wise equality.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @param  __last2   An input iterator.
   *  @param __binary_pred A binary predicate @link functors
   *                  functor@endlink.
   *  @return         A boolean true or false.
   *
   *  This compares the elements of two ranges using the binary_pred
   *  parameter, and returns true or
   *  false depending on whether all of the corresponding elements of the
   *  ranges are equal.
  */
  template<typename _IIter1, typename _IIter2, typename _BinaryPredicate>
    inline bool
    equal(_IIter1 __first1, _IIter1 __last1,
	  _IIter2 __first2, _IIter2 __last2, _BinaryPredicate __binary_pred)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_IIter1>)
      __glibcxx_function_requires(_InputIteratorConcept<_IIter2>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      using _RATag = random_access_iterator_tag;
      using _Cat1 = typename iterator_traits<_IIter1>::iterator_category;
      using _Cat2 = typename iterator_traits<_IIter2>::iterator_category;
      using _RAIters = __and_<is_same<_Cat1, _RATag>, is_same<_Cat2, _RATag>>;
      if (_RAIters())
	{
	  auto __d1 = std::distance(__first1, __last1);
	  auto __d2 = std::distance(__first2, __last2);
	  if (__d1 != __d2)
	    return false;
	  return _GLIBCXX_STD_A::equal(__first1, __last1, __first2,
				       __binary_pred);
	}

      for (; __first1 != __last1 && __first2 != __last2;
	  ++__first1, (void)++__first2)
	if (!bool(__binary_pred(*__first1, *__first2)))
	  return false;
      return __first1 == __last1 && __first2 == __last2;
    }
#endif

  /**
   *  @brief Performs @b dictionary comparison on ranges.
   *  @ingroup sorting_algorithms
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @param  __last2   An input iterator.
   *  @return   A boolean true or false.
   *
   *  <em>Returns true if the sequence of elements defined by the range
   *  [first1,last1) is lexicographically less than the sequence of elements
   *  defined by the range [first2,last2).  Returns false otherwise.</em>
   *  (Quoted from [25.3.8]/1.)  If the iterators are all character pointers,
   *  then this is an inline call to @c memcmp.
  */
  template<typename _II1, typename _II2>
    inline bool
    lexicographical_compare(_II1 __first1, _II1 __last1,
			    _II2 __first2, _II2 __last2)
    {
#ifdef _GLIBCXX_CONCEPT_CHECKS
      // concept requirements
      typedef typename iterator_traits<_II1>::value_type _ValueType1;
      typedef typename iterator_traits<_II2>::value_type _ValueType2;
#endif
      __glibcxx_function_requires(_InputIteratorConcept<_II1>)
      __glibcxx_function_requires(_InputIteratorConcept<_II2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType1, _ValueType2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType2, _ValueType1>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_irreflexive2(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);
      __glibcxx_requires_irreflexive2(__first2, __last2);

      return std::__lexicographical_compare_aux(std::__niter_base(__first1),
						std::__niter_base(__last1),
						std::__niter_base(__first2),
						std::__niter_base(__last2));
    }

  /**
   *  @brief Performs @b dictionary comparison on ranges.
   *  @ingroup sorting_algorithms
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @param  __last2   An input iterator.
   *  @param  __comp  A @link comparison_functors comparison functor@endlink.
   *  @return   A boolean true or false.
   *
   *  The same as the four-parameter @c lexicographical_compare, but uses the
   *  comp parameter instead of @c <.
  */
  template<typename _II1, typename _II2, typename _Compare>
    inline bool
    lexicographical_compare(_II1 __first1, _II1 __last1,
			    _II2 __first2, _II2 __last2, _Compare __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_II1>)
      __glibcxx_function_requires(_InputIteratorConcept<_II2>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
      __glibcxx_requires_valid_range(__first2, __last2);
      __glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);

      return std::__lexicographical_compare_impl
	(__first1, __last1, __first2, __last2,
	 __gnu_cxx::__ops::__iter_comp_iter(__comp));
    }

  template<typename _InputIterator1, typename _InputIterator2,
	   typename _BinaryPredicate>
    pair<_InputIterator1, _InputIterator2>
    __mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
	       _InputIterator2 __first2, _BinaryPredicate __binary_pred)
    {
      while (__first1 != __last1 && __binary_pred(__first1, __first2))
        {
	  ++__first1;
	  ++__first2;
        }
      return pair<_InputIterator1, _InputIterator2>(__first1, __first2);
    }

  /**
   *  @brief Finds the places in ranges which don't match.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @return   A pair of iterators pointing to the first mismatch.
   *
   *  This compares the elements of two ranges using @c == and returns a pair
   *  of iterators.  The first iterator points into the first range, the
   *  second iterator points into the second range, and the elements pointed
   *  to by the iterators are not equal.
  */
  template<typename _InputIterator1, typename _InputIterator2>
    inline pair<_InputIterator1, _InputIterator2>
    mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
	     _InputIterator2 __first2)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_InputIterator1>::value_type,
	    typename iterator_traits<_InputIterator2>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);

      return _GLIBCXX_STD_A::__mismatch(__first1, __last1, __first2,
			     __gnu_cxx::__ops::__iter_equal_to_iter());
    }

  /**
   *  @brief Finds the places in ranges which don't match.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @param __binary_pred A binary predicate @link functors
   *         functor@endlink.
   *  @return   A pair of iterators pointing to the first mismatch.
   *
   *  This compares the elements of two ranges using the binary_pred
   *  parameter, and returns a pair
   *  of iterators.  The first iterator points into the first range, the
   *  second iterator points into the second range, and the elements pointed
   *  to by the iterators are not equal.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _BinaryPredicate>
    inline pair<_InputIterator1, _InputIterator2>
    mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
	     _InputIterator2 __first2, _BinaryPredicate __binary_pred)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_requires_valid_range(__first1, __last1);

      return _GLIBCXX_STD_A::__mismatch(__first1, __last1, __first2,
	__gnu_cxx::__ops::__iter_comp_iter(__binary_pred));
    }

#if __cplusplus > 201103L

  template<typename _InputIterator1, typename _InputIterator2,
	   typename _BinaryPredicate>
    pair<_InputIterator1, _InputIterator2>
    __mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
	       _InputIterator2 __first2, _InputIterator2 __last2,
	       _BinaryPredicate __binary_pred)
    {
      while (__first1 != __last1 && __first2 != __last2
	     && __binary_pred(__first1, __first2))
        {
	  ++__first1;
	  ++__first2;
        }
      return pair<_InputIterator1, _InputIterator2>(__first1, __first2);
    }

  /**
   *  @brief Finds the places in ranges which don't match.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @param  __last2   An input iterator.
   *  @return   A pair of iterators pointing to the first mismatch.
   *
   *  This compares the elements of two ranges using @c == and returns a pair
   *  of iterators.  The first iterator points into the first range, the
   *  second iterator points into the second range, and the elements pointed
   *  to by the iterators are not equal.
  */
  template<typename _InputIterator1, typename _InputIterator2>
    inline pair<_InputIterator1, _InputIterator2>
    mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
	     _InputIterator2 __first2, _InputIterator2 __last2)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_InputIterator1>::value_type,
	    typename iterator_traits<_InputIterator2>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      return _GLIBCXX_STD_A::__mismatch(__first1, __last1, __first2, __last2,
			     __gnu_cxx::__ops::__iter_equal_to_iter());
    }

  /**
   *  @brief Finds the places in ranges which don't match.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @param  __last2   An input iterator.
   *  @param __binary_pred A binary predicate @link functors
   *         functor@endlink.
   *  @return   A pair of iterators pointing to the first mismatch.
   *
   *  This compares the elements of two ranges using the binary_pred
   *  parameter, and returns a pair
   *  of iterators.  The first iterator points into the first range, the
   *  second iterator points into the second range, and the elements pointed
   *  to by the iterators are not equal.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _BinaryPredicate>
    inline pair<_InputIterator1, _InputIterator2>
    mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
	     _InputIterator2 __first2, _InputIterator2 __last2,
	     _BinaryPredicate __binary_pred)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      return _GLIBCXX_STD_A::__mismatch(__first1, __last1, __first2, __last2,
			     __gnu_cxx::__ops::__iter_comp_iter(__binary_pred));
    }
#endif

_GLIBCXX_END_NAMESPACE_ALGO
} // namespace std

// NB: This file is included within many other C++ includes, as a way
// of getting the base algorithms. So, make sure that parallel bits
// come in too if requested. 
#ifdef _GLIBCXX_PARALLEL
# include <parallel/algobase.h>
#endif

#endif