libcxx/include/__algorithm/shuffle.h

//===----------------------------------------------------------------------===//
//
// 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_SHUFFLE_H
#define _LIBCPP___ALGORITHM_SHUFFLE_H

#include <__algorithm/iterator_operations.h>
#include <__config>
#include <__cstddef/ptrdiff_t.h>
#include <__iterator/iterator_traits.h>
#include <__random/uniform_int_distribution.h>
#include <__utility/forward.h>
#include <__utility/move.h>
#include <__utility/swap.h>
#include <cstdint>

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

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

class _LIBCPP_EXPORTED_FROM_ABI __libcpp_debug_randomizer {
public:
  _LIBCPP_HIDE_FROM_ABI __libcpp_debug_randomizer() {
    __state_ = __seed();
    __inc_   = __state_ + 0xda3e39cb94b95bdbULL;
    __inc_   = (__inc_ << 1) | 1;
  }
  typedef uint_fast32_t result_type;

  static const result_type _Min = 0;
  static const result_type _Max = 0xFFFFFFFF;

  _LIBCPP_HIDE_FROM_ABI result_type operator()() {
    uint_fast64_t __oldstate = __state_;
    __state_                 = __oldstate * 6364136223846793005ULL + __inc_;
    return __oldstate >> 32;
  }

  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR result_type min() { return _Min; }
  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR result_type max() { return _Max; }

private:
  uint_fast64_t __state_;
  uint_fast64_t __inc_;
  _LIBCPP_HIDE_FROM_ABI static uint_fast64_t __seed() {
#ifdef _LIBCPP_DEBUG_RANDOMIZE_UNSPECIFIED_STABILITY_SEED
    return _LIBCPP_DEBUG_RANDOMIZE_UNSPECIFIED_STABILITY_SEED;
#else
    static char __x;
    return reinterpret_cast<uintptr_t>(&__x);
#endif
  }
};

#if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_RANDOM_SHUFFLE) || defined(_LIBCPP_BUILDING_LIBRARY)
class _LIBCPP_EXPORTED_FROM_ABI __rs_default;

_LIBCPP_EXPORTED_FROM_ABI __rs_default __rs_get();

class _LIBCPP_EXPORTED_FROM_ABI __rs_default {
  static unsigned __c_;

  __rs_default();

public:
  typedef uint_fast32_t result_type;

  static const result_type _Min = 0;
  static const result_type _Max = 0xFFFFFFFF;

  __rs_default(const __rs_default&);
  ~__rs_default();

  result_type operator()();

  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR result_type min() { return _Min; }
  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR result_type max() { return _Max; }

  friend _LIBCPP_EXPORTED_FROM_ABI __rs_default __rs_get();
};

_LIBCPP_EXPORTED_FROM_ABI __rs_default __rs_get();

template <class _RandomAccessIterator>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX14 void
random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last) {
  typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
  typedef uniform_int_distribution<ptrdiff_t> _Dp;
  typedef typename _Dp::param_type _Pp;
  difference_type __d = __last - __first;
  if (__d > 1) {
    _Dp __uid;
    __rs_default __g = __rs_get();
    for (--__last, (void)--__d; __first < __last; ++__first, (void)--__d) {
      difference_type __i = __uid(__g, _Pp(0, __d));
      if (__i != difference_type(0))
        swap(*__first, *(__first + __i));
    }
  }
}

template <class _RandomAccessIterator, class _RandomNumberGenerator>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX14 void
random_shuffle(_RandomAccessIterator __first,
               _RandomAccessIterator __last,
#  ifndef _LIBCPP_CXX03_LANG
               _RandomNumberGenerator&& __rand)
#  else
               _RandomNumberGenerator& __rand)
#  endif
{
  typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
  difference_type __d = __last - __first;
  if (__d > 1) {
    for (--__last; __first < __last; ++__first, (void)--__d) {
      difference_type __i = __rand(__d);
      if (__i != difference_type(0))
        swap(*__first, *(__first + __i));
    }
  }
}
#endif

template <class _AlgPolicy, class _RandomAccessIterator, class _Sentinel, class _UniformRandomNumberGenerator>
_LIBCPP_HIDE_FROM_ABI _RandomAccessIterator
__shuffle(_RandomAccessIterator __first, _Sentinel __last_sentinel, _UniformRandomNumberGenerator&& __g) {
  typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
  typedef uniform_int_distribution<ptrdiff_t> _Dp;
  typedef typename _Dp::param_type _Pp;

  auto __original_last = _IterOps<_AlgPolicy>::next(__first, __last_sentinel);
  auto __last          = __original_last;
  difference_type __d  = __last - __first;
  if (__d > 1) {
    _Dp __uid;
    for (--__last, (void)--__d; __first < __last; ++__first, (void)--__d) {
      difference_type __i = __uid(__g, _Pp(0, __d));
      if (__i != difference_type(0))
        _IterOps<_AlgPolicy>::iter_swap(__first, __first + __i);
    }
  }

  return __original_last;
}

template <class _RandomAccessIterator, class _UniformRandomNumberGenerator>
_LIBCPP_HIDE_FROM_ABI void
shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last, _UniformRandomNumberGenerator&& __g) {
  (void)std::__shuffle<_ClassicAlgPolicy>(
      std::move(__first), std::move(__last), std::forward<_UniformRandomNumberGenerator>(__g));
}

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___ALGORITHM_SHUFFLE_H