libstdc++-v3/include/ext/algorithm

// Algorithm extensions -*- 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.

// 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
 * 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 ext/algorithm
 *  This file is a GNU extension to the Standard C++ Library (possibly
 *  containing extensions from the HP/SGI STL subset).
 */

#ifndef _EXT_ALGORITHM
#define _EXT_ALGORITHM 1

#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif

#include <bits/requires_hosted.h> // GNU extensions are currently omitted

#include <algorithm>

namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  //--------------------------------------------------
  // copy_n (not part of the C++ standard)

  template<typename _InputIterator, typename _Size, typename _OutputIterator>
    std::pair<_InputIterator, _OutputIterator>
    __copy_n(_InputIterator __first, _Size __count,
	     _OutputIterator __result,
	     std::input_iterator_tag)
    {
      for ( ; __count > 0; --__count)
	{
	  *__result = *__first;
	  ++__first;
	  ++__result;
	}
      return std::pair<_InputIterator, _OutputIterator>(__first, __result);
    }

  template<typename _RAIterator, typename _Size, typename _OutputIterator>
    inline std::pair<_RAIterator, _OutputIterator>
    __copy_n(_RAIterator __first, _Size __count,
	     _OutputIterator __result,
	     std::random_access_iterator_tag)
    {
      _RAIterator __last = __first + __count;
      return std::pair<_RAIterator, _OutputIterator>(__last, std::copy(__first,
								  __last,
								  __result));
    }

  /**
   *  @brief Copies the range [first,first+count) into [result,result+count).
   *  @param  __first  An input iterator.
   *  @param  __count  The number of elements to copy.
   *  @param  __result An output iterator.
   *  @return   A std::pair composed of first+count and result+count.
   *
   *  This is an SGI extension.
   *  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).
   *  @ingroup SGIextensions
  */
  template<typename _InputIterator, typename _Size, typename _OutputIterator>
    inline std::pair<_InputIterator, _OutputIterator>
    copy_n(_InputIterator __first, _Size __count, _OutputIterator __result)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
	    typename std::iterator_traits<_InputIterator>::value_type>)

      return __gnu_cxx::__copy_n(__first, __count, __result,
				 std::__iterator_category(__first));
    }

  template<typename _InputIterator1, typename _InputIterator2>
    int
    __lexicographical_compare_3way(_InputIterator1 __first1,
				   _InputIterator1 __last1,
				   _InputIterator2 __first2,
				   _InputIterator2 __last2)
    {
      while (__first1 != __last1 && __first2 != __last2)
	{
	  if (*__first1 < *__first2)
	    return -1;
	  if (*__first2 < *__first1)
	    return 1;
	  ++__first1;
	  ++__first2;
	}
      if (__first2 == __last2)
	return !(__first1 == __last1);
      else
	return -1;
    }

  inline int
  __lexicographical_compare_3way(const unsigned char* __first1,
				 const unsigned char* __last1,
				 const unsigned char* __first2,
				 const unsigned char* __last2)
  {
    const std::ptrdiff_t __len1 = __last1 - __first1;
    const std::ptrdiff_t __len2 = __last2 - __first2;
    const int __result = __builtin_memcmp(__first1, __first2,
					  (std::min)(__len1, __len2));
    return __result != 0 ? __result
			 : (__len1 == __len2 ? 0 : (__len1 < __len2 ? -1 : 1));
  }

  inline int
  __lexicographical_compare_3way(const char* __first1, const char* __last1,
				 const char* __first2, const char* __last2)
  {
#if CHAR_MAX == SCHAR_MAX
    return __lexicographical_compare_3way((const signed char*) __first1,
					  (const signed char*) __last1,
					  (const signed char*) __first2,
					  (const signed char*) __last2);
#else
    return __lexicographical_compare_3way((const unsigned char*) __first1,
					  (const unsigned char*) __last1,
					  (const unsigned char*) __first2,
					  (const unsigned char*) __last2);
#endif
  }

  /**
   *  @brief @c memcmp on steroids.
   *  @param  __first1  An input iterator.
   *  @param  __last1   An input iterator.
   *  @param  __first2  An input iterator.
   *  @param  __last2   An input iterator.
   *  @return   An int, as with @c memcmp.
   *
   *  The return value will be less than zero if the first range is
   *  <em>lexigraphically less than</em> the second, greater than zero
   *  if the second range is <em>lexigraphically less than</em> the
   *  first, and zero otherwise.
   *  This is an SGI extension.
   *  @ingroup SGIextensions
  */
  template<typename _InputIterator1, typename _InputIterator2>
    int
    lexicographical_compare_3way(_InputIterator1 __first1,
				 _InputIterator1 __last1,
				 _InputIterator2 __first2,
				 _InputIterator2 __last2)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename std::iterator_traits<_InputIterator1>::value_type>)
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename std::iterator_traits<_InputIterator2>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      return __lexicographical_compare_3way(__first1, __last1, __first2,
					    __last2);
    }

  // count and count_if: this version, whose return type is void, was present
  // in the HP STL, and is retained as an extension for backward compatibility.
  template<typename _InputIterator, typename _Tp, typename _Size>
    void
    count(_InputIterator __first, _InputIterator __last,
	  const _Tp& __value,
	  _Size& __n)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_EqualityComparableConcept<
	    typename std::iterator_traits<_InputIterator>::value_type >)
      __glibcxx_function_requires(_EqualityComparableConcept<_Tp>)
      __glibcxx_requires_valid_range(__first, __last);

      for ( ; __first != __last; ++__first)
	if (*__first == __value)
	  ++__n;
    }

  template<typename _InputIterator, typename _Predicate, typename _Size>
    void
    count_if(_InputIterator __first, _InputIterator __last,
	     _Predicate __pred,
	     _Size& __n)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	    typename std::iterator_traits<_InputIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      for ( ; __first != __last; ++__first)
	if (__pred(*__first))
	  ++__n;
    }

  // random_sample and random_sample_n (extensions, not part of the standard).

  /**
   *  This is an SGI extension.
   *  @ingroup SGIextensions
   *  @doctodo
  */
  template<typename _ForwardIterator, typename _OutputIterator,
	   typename _Distance>
    _OutputIterator
    random_sample_n(_ForwardIterator __first, _ForwardIterator __last,
                    _OutputIterator __out, const _Distance __n)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
		typename std::iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      _Distance __remaining = std::distance(__first, __last);
      _Distance __m = (std::min)(__n, __remaining);

      while (__m > 0)
	{
	  if ((std::rand() % __remaining) < __m)
	    {
	      *__out = *__first;
	      ++__out;
	      --__m;
	    }
	  --__remaining;
	  ++__first;
	}
      return __out;
    }

  /**
   *  This is an SGI extension.
   *  @ingroup SGIextensions
   *  @doctodo
  */
  template<typename _ForwardIterator, typename _OutputIterator,
	   typename _Distance, typename _RandomNumberGenerator>
    _OutputIterator
    random_sample_n(_ForwardIterator __first, _ForwardIterator __last,
                   _OutputIterator __out, const _Distance __n,
		   _RandomNumberGenerator& __rand)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
		typename std::iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_function_requires(_UnaryFunctionConcept<
		_RandomNumberGenerator, _Distance, _Distance>)
      __glibcxx_requires_valid_range(__first, __last);

      _Distance __remaining = std::distance(__first, __last);
      _Distance __m = (std::min)(__n, __remaining);

      while (__m > 0)
	{
	  if (__rand(__remaining) < __m)
	    {
	      *__out = *__first;
	      ++__out;
	      --__m;
	    }
	  --__remaining;
	  ++__first;
	}
      return __out;
    }

  template<typename _InputIterator, typename _RandomAccessIterator,
	   typename _Distance>
    _RandomAccessIterator
    __random_sample(_InputIterator __first, _InputIterator __last,
		    _RandomAccessIterator __out,
		    const _Distance __n)
    {
      _Distance __m = 0;
      _Distance __t = __n;
      for ( ; __first != __last && __m < __n; ++__m, ++__first)
	__out[__m] = *__first;

      while (__first != __last)
	{
	  ++__t;
	  _Distance __M = std::rand() % (__t);
	  if (__M < __n)
	    __out[__M] = *__first;
	  ++__first;
	}
      return __out + __m;
    }

  template<typename _InputIterator, typename _RandomAccessIterator,
	   typename _RandomNumberGenerator, typename _Distance>
    _RandomAccessIterator
    __random_sample(_InputIterator __first, _InputIterator __last,
		    _RandomAccessIterator __out,
		    _RandomNumberGenerator& __rand,
		    const _Distance __n)
    {
      // concept requirements
      __glibcxx_function_requires(_UnaryFunctionConcept<
	    _RandomNumberGenerator, _Distance, _Distance>)

      _Distance __m = 0;
      _Distance __t = __n;
      for ( ; __first != __last && __m < __n; ++__m, ++__first)
	__out[__m] = *__first;

      while (__first != __last)
	{
	  ++__t;
	  _Distance __M = __rand(__t);
	  if (__M < __n)
	    __out[__M] = *__first;
	  ++__first;
	}
      return __out + __m;
    }

  /**
   *  This is an SGI extension.
   *  @ingroup SGIextensions
   *  @doctodo
  */
  template<typename _InputIterator, typename _RandomAccessIterator>
    inline _RandomAccessIterator
    random_sample(_InputIterator __first, _InputIterator __last,
		  _RandomAccessIterator __out_first,
		  _RandomAccessIterator __out_last)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_requires_valid_range(__first, __last);
      __glibcxx_requires_valid_range(__out_first, __out_last);

      return __random_sample(__first, __last,
			     __out_first, __out_last - __out_first);
    }

  /**
   *  This is an SGI extension.
   *  @ingroup SGIextensions
   *  @doctodo
  */
  template<typename _InputIterator, typename _RandomAccessIterator,
	   typename _RandomNumberGenerator>
    inline _RandomAccessIterator
    random_sample(_InputIterator __first, _InputIterator __last,
		  _RandomAccessIterator __out_first,
		  _RandomAccessIterator __out_last,
		  _RandomNumberGenerator& __rand)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_requires_valid_range(__first, __last);
      __glibcxx_requires_valid_range(__out_first, __out_last);

      return __random_sample(__first, __last,
			     __out_first, __rand,
			     __out_last - __out_first);
    }

#if __cplusplus >= 201103L
  using std::is_heap;
#else
  /**
   *  This is an SGI extension.
   *  @ingroup SGIextensions
   *  @doctodo
  */
  template<typename _RandomAccessIterator>
    inline bool
    is_heap(_RandomAccessIterator __first, _RandomAccessIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_RandomAccessIteratorConcept<
				  _RandomAccessIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename std::iterator_traits<_RandomAccessIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      return std::__is_heap(__first, __last - __first);
    }

  /**
   *  This is an SGI extension.
   *  @ingroup SGIextensions
   *  @doctodo
  */
  template<typename _RandomAccessIterator, typename _StrictWeakOrdering>
    inline bool
    is_heap(_RandomAccessIterator __first, _RandomAccessIterator __last,
	    _StrictWeakOrdering __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_RandomAccessIteratorConcept<
				  _RandomAccessIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_StrictWeakOrdering,
	    typename std::iterator_traits<_RandomAccessIterator>::value_type,
	    typename std::iterator_traits<_RandomAccessIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      return std::__is_heap(__first, __comp, __last - __first);
    }
#endif

#if __cplusplus >= 201103L
  using std::is_sorted;
#else
  // is_sorted, a predicated testing whether a range is sorted in
  // nondescending order.  This is an extension, not part of the C++
  // standard.

  /**
   *  This is an SGI extension.
   *  @ingroup SGIextensions
   *  @doctodo
  */
  template<typename _ForwardIterator>
    bool
    is_sorted(_ForwardIterator __first, _ForwardIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename std::iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return true;

      _ForwardIterator __next = __first;
      for (++__next; __next != __last; __first = __next, ++__next)
	if (*__next < *__first)
	  return false;
      return true;
    }

  /**
   *  This is an SGI extension.
   *  @ingroup SGIextensions
   *  @doctodo
  */
  template<typename _ForwardIterator, typename _StrictWeakOrdering>
    bool
    is_sorted(_ForwardIterator __first, _ForwardIterator __last,
	      _StrictWeakOrdering __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_StrictWeakOrdering,
	    typename std::iterator_traits<_ForwardIterator>::value_type,
	    typename std::iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return true;

      _ForwardIterator __next = __first;
      for (++__next; __next != __last; __first = __next, ++__next)
	if (__comp(*__next, *__first))
	  return false;
      return true;
    }
#endif  // C++11

  /**
   *  @brief Find the median of three values.
   *  @param  __a  A value.
   *  @param  __b  A value.
   *  @param  __c  A value.
   *  @return One of @p a, @p b or @p c.
   *
   *  If @c {l,m,n} is some convolution of @p {a,b,c} such that @c l<=m<=n
   *  then the value returned will be @c m.
   *  This is an SGI extension.
   *  @ingroup SGIextensions
  */
  template<typename _Tp>
    const _Tp&
    __median(const _Tp& __a, const _Tp& __b, const _Tp& __c)
    {
      // concept requirements
      __glibcxx_function_requires(_LessThanComparableConcept<_Tp>)
      if (__a < __b)
	if (__b < __c)
	  return __b;
	else if (__a < __c)
	  return __c;
	else
	  return __a;
      else if (__a < __c)
	return __a;
      else if (__b < __c)
	return __c;
      else
	return __b;
    }

  /**
   *  @brief Find the median of three values using a predicate for comparison.
   *  @param  __a     A value.
   *  @param  __b     A value.
   *  @param  __c     A value.
   *  @param  __comp  A binary predicate.
   *  @return One of @p a, @p b or @p c.
   *
   *  If @c {l,m,n} is some convolution of @p {a,b,c} such that @p comp(l,m)
   *  and @p comp(m,n) are both true then the value returned will be @c m.
   *  This is an SGI extension.
   *  @ingroup SGIextensions
  */
  template<typename _Tp, typename _Compare>
    const _Tp&
    __median(const _Tp& __a, const _Tp& __b, const _Tp& __c, _Compare __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_BinaryFunctionConcept<_Compare, bool,
				                         _Tp, _Tp>)
      if (__comp(__a, __b))
	if (__comp(__b, __c))
	  return __b;
	else if (__comp(__a, __c))
	  return __c;
	else
	  return __a;
      else if (__comp(__a, __c))
	return __a;
      else if (__comp(__b, __c))
	return __c;
      else
	return __b;
    }

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif /* _EXT_ALGORITHM */