cuda_toolkit/include/__iterator/advance.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// 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
// SPDX-FileCopyrightText: Copyright (c) 2023 NVIDIA CORPORATION & AFFILIATES.
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCUDACXX___ITERATOR_ADVANCE_H
#define _LIBCUDACXX___ITERATOR_ADVANCE_H

#ifndef __cuda_std__
#  include <__config>
#endif // __cuda_std__

#include "../__assert"
#include "../__concepts/assignable.h"
#include "../__concepts/same_as.h"
#include "../__iterator/concepts.h"
#include "../__iterator/incrementable_traits.h"
#include "../__iterator/iterator_traits.h"
#include "../__utility/convert_to_integral.h"
#include "../__utility/move.h"
#include "../cstdlib"

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header

_LIBCUDACXX_BEGIN_NAMESPACE_STD

template <class _InputIter>
_LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_CONSTEXPR_AFTER_CXX14 void
__advance(_InputIter& __i, typename iterator_traits<_InputIter>::difference_type __n, input_iterator_tag)
{
  for (; __n > 0; --__n)
  {
    ++__i;
  }
}

template <class _BiDirIter>
_LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_CONSTEXPR_AFTER_CXX14 void
__advance(_BiDirIter& __i, typename iterator_traits<_BiDirIter>::difference_type __n, bidirectional_iterator_tag)
{
  if (__n >= 0)
  {
    for (; __n > 0; --__n)
    {
      ++__i;
    }
  }
  else
  {
    for (; __n < 0; ++__n)
    {
      --__i;
    }
  }
}

template <class _RandIter>
_LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_CONSTEXPR_AFTER_CXX14 void
__advance(_RandIter& __i, typename iterator_traits<_RandIter>::difference_type __n, random_access_iterator_tag)
{
  __i += __n;
}

template < class _InputIter,
           class _Distance,
           class _IntegralDistance = decltype(_CUDA_VSTD::__convert_to_integral(_CUDA_VSTD::declval<_Distance>())),
           class                   = __enable_if_t<is_integral<_IntegralDistance>::value> >
_LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_CONSTEXPR_AFTER_CXX14 void advance(_InputIter& __i, _Distance __orig_n)
{
  typedef typename iterator_traits<_InputIter>::difference_type _Difference;
  _Difference __n = static_cast<_Difference>(_CUDA_VSTD::__convert_to_integral(__orig_n));
  _LIBCUDACXX_ASSERT(__n >= 0 || __is_cpp17_bidirectional_iterator<_InputIter>::value,
                     "Attempt to advance(it, n) with negative n on a non-bidirectional iterator");
  _CUDA_VSTD::__advance(__i, __n, typename iterator_traits<_InputIter>::iterator_category());
}

_LIBCUDACXX_END_NAMESPACE_STD

#if _LIBCUDACXX_STD_VER > 14 && !defined(_LICBUDACXX_COMPILER_MSVC_2017)

// [range.iter.op.advance]

_LIBCUDACXX_BEGIN_NAMESPACE_RANGES
_LIBCUDACXX_BEGIN_NAMESPACE_CPO(__advance)
struct __fn
{
private:
  template <class _Ip>
  _LIBCUDACXX_INLINE_VISIBILITY static constexpr void __advance_forward(_Ip& __i, iter_difference_t<_Ip> __n)
  {
    while (__n > 0)
    {
      --__n;
      ++__i;
    }
  }

  template <class _Ip>
  _LIBCUDACXX_INLINE_VISIBILITY static constexpr void __advance_backward(_Ip& __i, iter_difference_t<_Ip> __n)
  {
    while (__n < 0)
    {
      ++__n;
      --__i;
    }
  }

  template <class _Iter_difference>
  _LIBCUDACXX_INLINE_VISIBILITY static constexpr auto
  __magnitude_geq(_Iter_difference __a, _Iter_difference __b) noexcept
  {
    return __a == 0 ? __b == 0 : //
             __a > 0 ? __a >= __b
                     : __a <= __b;
  };

public:
  // Preconditions: If `I` does not model `bidirectional_iterator`, `n` is not negative.

  _LIBCUDACXX_TEMPLATE(class _Ip)
  _LIBCUDACXX_REQUIRES(input_or_output_iterator<_Ip>)
  _LIBCUDACXX_HIDE_FROM_ABI _LIBCUDACXX_INLINE_VISIBILITY constexpr void
  operator()(_Ip& __i, iter_difference_t<_Ip> __n) const
  {
    _LIBCUDACXX_ASSERT(__n >= 0 || bidirectional_iterator<_Ip>,
                       "If `n < 0`, then `bidirectional_iterator<I>` must be true.");

    // If `I` models `random_access_iterator`, equivalent to `i += n`.
    if constexpr (random_access_iterator<_Ip>)
    {
      __i += __n;
      return;
    }
    else if constexpr (bidirectional_iterator<_Ip>)
    {
      // Otherwise, if `n` is non-negative, increments `i` by `n`.
      __advance_forward(__i, __n);
      // Otherwise, decrements `i` by `-n`.
      __advance_backward(__i, __n);
      return;
    }
    else
    {
      // Otherwise, if `n` is non-negative, increments `i` by `n`.
      __advance_forward(__i, __n);
      return;
    }
  }

  _LIBCUDACXX_TEMPLATE(class _Ip, class _Sp)
  _LIBCUDACXX_REQUIRES(input_or_output_iterator<_Ip> _LIBCUDACXX_AND sentinel_for<_Sp, _Ip>)
  _LIBCUDACXX_HIDE_FROM_ABI _LIBCUDACXX_INLINE_VISIBILITY constexpr void operator()(_Ip& __i, _Sp __bound_sentinel) const
  {
    // If `I` and `S` model `assignable_from<I&, S>`, equivalent to `i = std::move(bound_sentinel)`.
    if constexpr (assignable_from<_Ip&, _Sp>)
    {
      __i = _CUDA_VSTD::move(__bound_sentinel);
    }
    // Otherwise, if `S` and `I` model `sized_sentinel_for<S, I>`,
    // equivalent to `ranges::advance(i, bound_sentinel - i)`.
    else if constexpr (sized_sentinel_for<_Sp, _Ip>)
    {
      (*this)(__i, __bound_sentinel - __i);
    }
    // Otherwise, while `bool(i != bound_sentinel)` is true, increments `i`.
    else
    {
      while (__i != __bound_sentinel)
      {
        ++__i;
      }
    }
  }

  // Preconditions:
  //   * If `n > 0`, [i, bound_sentinel) denotes a range.
  //   * If `n == 0`, [i, bound_sentinel) or [bound_sentinel, i) denotes a range.
  //   * If `n < 0`, [bound_sentinel, i) denotes a range, `I` models `bidirectional_iterator`,
  //     and `I` and `S` model `same_as<I, S>`.
  // Returns: `n - M`, where `M` is the difference between the ending and starting position.
  _LIBCUDACXX_TEMPLATE(class _Ip, class _Sp)
  _LIBCUDACXX_REQUIRES(input_or_output_iterator<_Ip> _LIBCUDACXX_AND sentinel_for<_Sp, _Ip>)
  _LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_HIDE_FROM_ABI constexpr iter_difference_t<_Ip>
  operator()(_Ip& __i, iter_difference_t<_Ip> __n, _Sp __bound_sentinel) const
  {
    _LIBCUDACXX_ASSERT((__n >= 0) || (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>),
                       "If `n < 0`, then `bidirectional_iterator<I> && same_as<I, S>` must be true.");
    // If `S` and `I` model `sized_sentinel_for<S, I>`:
    if constexpr (sized_sentinel_for<_Sp, _Ip>)
    {
      // If |n| >= |bound_sentinel - i|, equivalent to `ranges::advance(i, bound_sentinel)`.
      // __magnitude_geq(a, b) returns |a| >= |b|, assuming they have the same sign.
      const auto __M = __bound_sentinel - __i;
      if (__magnitude_geq(__n, __M))
      {
        (*this)(__i, __bound_sentinel);
        return __n - __M;
      }

      // Otherwise, equivalent to `ranges::advance(i, n)`.
      (*this)(__i, __n);
      return 0;
    }
    else
    {
      // Otherwise, if `n` is non-negative, while `bool(i != bound_sentinel)` is true, increments `i` but at
      // most `n` times.
      while (__i != __bound_sentinel && __n > 0)
      {
        ++__i;
        --__n;
      }

      // Otherwise, while `bool(i != bound_sentinel)` is true, decrements `i` but at most `-n` times.
      if constexpr (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>)
      {
        while (__i != __bound_sentinel && __n < 0)
        {
          --__i;
          ++__n;
        }
      }
      return __n;
    }
    _LIBCUDACXX_UNREACHABLE();
  }
};
_LIBCUDACXX_END_NAMESPACE_CPO

inline namespace __cpo
{
_LIBCUDACXX_CPO_ACCESSIBILITY auto advance = __advance::__fn{};
} // namespace __cpo

_LIBCUDACXX_END_NAMESPACE_RANGES

#endif // _LIBCUDACXX_STD_VER > 14 && !_LICBUDACXX_COMPILER_MSVC_2017

#endif // _LIBCUDACXX___ITERATOR_ADVANCE_H