text: // -*-Mode: C++;-*-
  
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  #ifndef HPCTOOLKIT_PROFILE_MPI_SCAN_H
  #define HPCTOOLKIT_PROFILE_MPI_SCAN_H
  
  #include "core.hpp"
  
  #include "../stdshim/optional.hpp"
  
  #include <array>
  
  namespace hpctoolkit::mpi {
  
  namespace detail {
  // NOTE: These are in-place operations, for efficiency.
  void scan(void* data, std::size_t cnt, const Datatype&, const Op&);
  void exscan(void* data, std::size_t cnt, const Datatype&, const Op&);
  }  // namespace detail
  
  /// Inclusive scan operation. Returns the accumulation of the values given
  /// here and in all other lesser rank indices. Returns the resulting value.
  template<class T, std::void_t<decltype(detail::asDatatype<T>())>* = nullptr>
  T scan(T data, const Op& op) {
    detail::scan(&data, 1, detail::asDatatype<T>(), op);
    return data;
  }
  
  /// Exclusive scan operation. Effectively the inclusive scan without including
  /// the current process's contribution. Note that no value is returned in rank
  /// 0, thus the need for an optional return value.
  template<class T, std::void_t<decltype(detail::asDatatype<T>())>* = nullptr>
  stdshim::optional<T> exscan(T data, const Op& op) {
    detail::exscan(&data, 1, detail::asDatatype<T>(), op);
    if(World::rank() == 0) return {};
    return data;
  }
  
  /// Inclusive scan operation. Variant to disable the usage of pointers.
  template<class T>
  T* scan(T*, const Op&) = delete;
  
  /// Exclusive scan operation. Variant to disable the usage of pointers.
  template<class T>
  T* exscan(T*, const Op&) = delete;
  
  /// Inclusive scan operation. Variant to allow for the usage of std::array.
  template<class T, std::size_t N>
  std::array<T, N> scan(std::array<T, N> data, const Op& op) {
    detail::scan(data.data(), N, detail::asDatatype<T>(), op);
    return data;
  }
  
  /// Exclusive scan operation. Variant to allow for the usage of std::array.
  template<class T, std::size_t N>
  stdshim::optional<std::array<T, N>> exscan(std::array<T, N> data, const Op& op) {
    detail::exscan(data.data(), N, detail::asDatatype<T>(), op);
    if(World::rank() == 0) return {};
    return data;
  }
  
  }  // namespace hpctoolkit::mpi
  
  #endif  // HPCTOOLKIT_PROFILE_MPI_REDUCE_H
  