xref: /freebsd-11.0-release/contrib/libc++/include/experimental/algorithm

// -*- C++ -*-
//===-------------------------- algorithm ---------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_EXPERIMENTAL_ALGORITHM
#define _LIBCPP_EXPERIMENTAL_ALGORITHM

/*
   experimental/algorithm synopsis

#include <algorithm>

namespace std {
namespace experimental {
inline namespace fundamentals_v1 {

template <class ForwardIterator, class Searcher>
ForwardIterator search(ForwardIterator first, ForwardIterator last,
                       const Searcher &searcher);
template <class PopulationIterator, class SampleIterator, class Distance,
          class UniformRandomNumberGenerator>
SampleIterator sample(PopulationIterator first, PopulationIterator last,
                      SampleIterator out, Distance n,
                      UniformRandomNumberGenerator &&g);

} // namespace fundamentals_v1
} // namespace experimental
} // namespace std

*/

#include <experimental/__config>
#include <algorithm>
#include <type_traits>

#include <__undef_min_max>

#include <__debug>

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

_LIBCPP_BEGIN_NAMESPACE_LFTS


template <class _PopulationIterator, class _SampleIterator, class _Distance,
          class _UniformRandomNumberGenerator>
_LIBCPP_INLINE_VISIBILITY
_SampleIterator __sample(_PopulationIterator __first,
                         _PopulationIterator __last, _SampleIterator __out,
                         _Distance __n,
                         _UniformRandomNumberGenerator &&__g,
                         input_iterator_tag) {

  _Distance __k = 0;
  for (; __first != __last && __k < __n; ++__first, (void)++__k)
    __out[__k] = *__first;
  _Distance __sz = __k;
  for (; __first != __last; ++__first, (void)++__k) {
    _Distance __r = _VSTD::uniform_int_distribution<_Distance>(0, __k)(__g);
    if (__r < __sz)
      __out[__r] = *__first;
  }
  return __out + _VSTD::min(__n, __k);
}

template <class _PopulationIterator, class _SampleIterator, class _Distance,
          class _UniformRandomNumberGenerator>
_LIBCPP_INLINE_VISIBILITY
_SampleIterator __sample(_PopulationIterator __first,
                         _PopulationIterator __last, _SampleIterator __out,
                         _Distance __n,
                         _UniformRandomNumberGenerator &&__g,
                         forward_iterator_tag) {
  _Distance __unsampled_sz = _VSTD::distance(__first, __last);
  for (__n = _VSTD::min(__n, __unsampled_sz); __n != 0; ++__first) {
    _Distance __r =
        _VSTD::uniform_int_distribution<_Distance>(0, --__unsampled_sz)(__g);
    if (__r < __n) {
      *__out++ = *__first;
      --__n;
    }
  }
  return __out;
}

template <class _PopulationIterator, class _SampleIterator, class _Distance,
          class _UniformRandomNumberGenerator>
_LIBCPP_INLINE_VISIBILITY
_SampleIterator sample(_PopulationIterator __first,
                         _PopulationIterator __last, _SampleIterator __out,
                         _Distance __n, _UniformRandomNumberGenerator &&__g) {
  typedef typename iterator_traits<_PopulationIterator>::iterator_category
        _PopCategory;
  typedef typename iterator_traits<_PopulationIterator>::difference_type
        _Difference;
  typedef typename common_type<_Distance, _Difference>::type _CommonType;
  _LIBCPP_ASSERT(__n >= 0, "N must be a positive number.");
  return _VSTD_LFTS::__sample(
      __first, __last, __out, _CommonType(__n),
      _VSTD::forward<_UniformRandomNumberGenerator>(__g),
      _PopCategory());
}

_LIBCPP_END_NAMESPACE_LFTS

#endif /* _LIBCPP_EXPERIMENTAL_ALGORITHM */