tuple.hpp

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#pragma once

#include <cute/config.hpp>
#include <cute/util/type_traits.hpp>
#include <cute/numeric/integral_constant.hpp>  // cute::true_type, cute::false_type
#include <cute/numeric/integer_sequence.hpp>

#include <cute/container/cuda_types.hpp>

//#include <cute/container/array.hpp>            // Advanced optimizations

//
// cute::tuple is like std::tuple, with two differences.
//
// 1. It works on both host and device.
// 2. Its template arguments must be semiregular types.
//
// Semiregular types are default constructible and copyable.
// They include "value types" like int or float,
// but do _not_ include references like int& or float&.
// (See std::tie for an example of a tuple of references.)
//
// This is simplified over the implementations in std::, cuda::std::, and thrust:: by ignoring much of
//    the conversion SFINAE, special overloading, and avoiding cvref template types.
//    Furthermore, the empty base optimization (EBO) is MORE aggressive by avoiding
//    construction calls, and ignoring any need for unique element addresses.
//
// Over standard-conforming tuple implementations, this appears to accelerate compilation times by over 3x.

namespace cute
{

namespace detail
{

// EBO stands for "empty base optimization."
// We use this technique to ensure that cute::tuple
// doesn't need to waste space storing any template arguments
// of cute::tuple that have no data (like integral_constant).
// Otherwise, cute::tuple would need to spend at least 1 byte
// for each of its template arguments.
//
// EBO always "holds" a single value of type T.
// N is like an array index that TupleBase uses
// to access the desired tuple element.
template <size_t N, class T, bool IsEmpty = is_empty<T>::value>
struct EBO;

// Specialization for types T that have no data;
// the "static tuple leaf."  Valid T here include
// integral_constant<U, Value>, Int<Value>,
// and any other semiregular type
// for which std::is_empty_v<T> is true.
template <size_t N, class T>
struct EBO<N, T, true>
{
  CUTE_HOST_DEVICE constexpr
  EBO() {}

  CUTE_HOST_DEVICE constexpr
  EBO(T const&) {}
};

template <size_t N, class T>
CUTE_HOST_DEVICE constexpr T getv(EBO<N, T, true> const&)
{ return {}; }

// Specialization for types T that are not empty;
// the "dynamic tuple leaf."  Valid T here include int,
// any other integral or floating-point type,
// or any semiregular type for which std::is_empty_v<T> is false.
template <size_t N, class T>
struct EBO<N, T, false>
{
  CUTE_HOST_DEVICE constexpr
  EBO() : t_{} {}

  template <class U>
  CUTE_HOST_DEVICE constexpr
  EBO(U const& u) : t_{u} {}

  T t_;
};

template <size_t N, class T>
CUTE_HOST_DEVICE constexpr T const& getv(EBO<N, T, false> const& x)
{ return x.t_; }

template <size_t N, class T>
CUTE_HOST_DEVICE constexpr T& getv(EBO<N, T, false>& x)
{ return x.t_; }

template <size_t N, class T>
CUTE_HOST_DEVICE constexpr T&& getv(EBO<N, T, false>&& x)
{ return static_cast<T&&>(x.t_); }

template <class IdxSeq, class... T>
struct TupleBase;

// Base class of cute::tuple.
// It inherits from EBO<i, t> for each (i, t) in (I..., T...).
// The actual storage (for nonempty t) lives in the base classes.
// index_sequence is a way to wrap up a sequence of zero or more
// compile-time integer values in a single type.
// We only ever use index_sequence<0, 1, ..., sizeof...(T)> in practice,
// as the type alias TupleBase below indicates.
template <size_t... I, class... T>
struct TupleBase<index_sequence<I...>, T...>
    : EBO<I,T>...
{
  CUTE_HOST_DEVICE constexpr
  TupleBase() {}

  template <class... U>
  CUTE_HOST_DEVICE constexpr explicit
  TupleBase(U const&... u)
      : EBO<I,T>(u)... {}

  template <class... U>
  CUTE_HOST_DEVICE constexpr
  TupleBase(TupleBase<index_sequence<I...>, U...> const& u)
      : EBO<I,T>(getv(static_cast<EBO<I,U> const&>(u)))... {}
};

} // end namespace detail

// Attempting to use the following commented-out alias
// in the declaration of `struct tuple` causes MSVC 2022 build errors.
//
//template <class... T>
//using TupleBase = detail::TupleBase<make_index_sequence<sizeof...(T)>, T...>;

// This is the actual cute::tuple class.
// The storage (if any) lives in TupleBase's EBO base classes.
//
// Inheriting from the above alias TupleBase
// causes MSVC 2022 build errors when assigning one tuple to another:
//
// illegal member initialization:
// 'TupleBase< /* template arguments */ >' is not a base or member
//
// Not using the alias or any kind of alias fixed the errors.
// In summary: this is verbose as a work-around for MSVC build errors.
template <class... T>
struct tuple : detail::TupleBase<make_index_sequence<sizeof...(T)>, T...>
{
  CUTE_HOST_DEVICE constexpr
  tuple() {}

  template <class... U>
  CUTE_HOST_DEVICE constexpr
  tuple(U const&... u) : detail::TupleBase<make_index_sequence<sizeof...(T)>, T...>(u...) {}

  template <class... U>
  CUTE_HOST_DEVICE constexpr
  tuple(tuple<U...> const& u)
      : detail::TupleBase<make_index_sequence<sizeof...(T)>, T...>(static_cast<detail::TupleBase<make_index_sequence<sizeof...(U)>, U...> const&>(u)) {}
};

//
// get for cute::tuple (just like std::get for std::tuple)
//

template <size_t I, class... T>
CUTE_HOST_DEVICE constexpr
decltype(auto)
get(tuple<T...> const& t) noexcept
{
  static_assert(I < sizeof...(T), "Index out of range");
  return detail::getv<I>(t);
}

template <size_t I, class... T>
CUTE_HOST_DEVICE constexpr
decltype(auto)
get(tuple<T...>& t) noexcept
{
  static_assert(I < sizeof...(T), "Index out of range");
  return detail::getv<I>(t);
}

template <size_t I, class... T>
CUTE_HOST_DEVICE constexpr
decltype(auto)
get(tuple<T...>&& t) noexcept
{
  static_assert(I < sizeof...(T), "Index out of range");
  return detail::getv<I>(static_cast<tuple<T...>&&>(t));
}

//
// Custom is_tuple trait simply checks the existence of tuple_size
//      and assumes std::get<I>(.), std::tuple_element<I,.>
//
namespace detail {

template <class T>
auto has_tuple_size( T*) -> integral_constant<bool, 0 <= tuple_size<T>::value>;
auto has_tuple_size(...) -> false_type;

} // end namespace detail

template <class T>
struct is_tuple : decltype(detail::has_tuple_size((T*)0)) {};

//
// make_tuple (value-based implementation)
//

template <class... T>
CUTE_HOST_DEVICE constexpr
tuple<T...>
make_tuple(T const&... t)
{
  return {t...};
}

//
// tuple_cat concatenates multiple cute::tuple into a single cute::tuple,
// just like std::tuple_cat for std::tuple.
//

#if 0
// Original implementation

namespace detail {

template <class T0, class T1,
          size_t... I0, size_t... I1>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1,
          index_sequence<I0...>, index_sequence<I1...>)
{
  return cute::make_tuple(get<I0>(t0)..., get<I1>(t1)...);
}

} // end namespace detail

CUTE_HOST_DEVICE constexpr
tuple<>
tuple_cat()
{
  return {};
}

template <class Tuple,
          __CUTE_REQUIRES(is_tuple<Tuple>::value)>
CUTE_HOST_DEVICE constexpr
Tuple const&
tuple_cat(Tuple const& t)
{
  return t;
}

template <class T0, class T1>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1)
{
  return detail::tuple_cat(t0, t1,
                           make_index_sequence<tuple_size<T0>::value>{},
                           make_index_sequence<tuple_size<T1>::value>{});
}

template <class T0, class T1, class T2, class... Ts>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1, T2 const& t2, Ts const&... ts)
{
  return cute::tuple_cat(cute::tuple_cat(t0,t1),t2,ts...);
}
#endif

#if 1
// Extended implementation

namespace detail {

template <class T0, class T1,
          size_t... I0, size_t... I1>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1,
          index_sequence<I0...>, index_sequence<I1...>)
{
  return cute::make_tuple(get<I0>(t0)..., get<I1>(t1)...);
}

template <class T0, class T1, class T2,
          size_t... I0, size_t... I1, size_t... I2>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1, T2 const& t2,
          index_sequence<I0...>, index_sequence<I1...>, index_sequence<I2...>)
{
  return cute::make_tuple(get<I0>(t0)..., get<I1>(t1)..., get<I2>(t2)...);
}

template <class T0, class T1, class T2, class T3,
          size_t... I0, size_t... I1, size_t... I2, size_t... I3>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1, T2 const& t2, T3 const& t3,
          index_sequence<I0...>, index_sequence<I1...>, index_sequence<I2...>, index_sequence<I3...>)
{
  return cute::make_tuple(get<I0>(t0)..., get<I1>(t1)..., get<I2>(t2)..., get<I3>(t3)...);
}

template <class T0, class T1, class T2, class T3, class T4,
          size_t... I0, size_t... I1, size_t... I2, size_t... I3, size_t... I4>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1, T2 const& t2, T3 const& t3, T4 const& t4,
          index_sequence<I0...>, index_sequence<I1...>, index_sequence<I2...>, index_sequence<I3...>, index_sequence<I4...>)
{
  return cute::make_tuple(get<I0>(t0)..., get<I1>(t1)..., get<I2>(t2)..., get<I3>(t3)..., get<I4>(t4)...);
}

} // end namespace detail

CUTE_HOST_DEVICE constexpr
tuple<>
tuple_cat()
{
  return {};
}

template <class Tuple,
          __CUTE_REQUIRES(is_tuple<Tuple>::value)>
CUTE_HOST_DEVICE constexpr
Tuple const&
tuple_cat(Tuple const& t)
{
  return t;
}

template <class T0, class T1>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1)
{
  return detail::tuple_cat(t0, t1,
                           make_index_sequence<tuple_size<T0>::value>{},
                           make_index_sequence<tuple_size<T1>::value>{});
}

template <class T0, class T1, class T2>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1, T2 const& t2)
{
  return detail::tuple_cat(t0, t1, t2,
                           make_index_sequence<tuple_size<T0>::value>{},
                           make_index_sequence<tuple_size<T1>::value>{},
                           make_index_sequence<tuple_size<T2>::value>{});
}

template <class T0, class T1, class T2, class T3>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1, T2 const& t2, T3 const& t3)
{
  return detail::tuple_cat(t0, t1, t2, t3,
                           make_index_sequence<tuple_size<T0>::value>{},
                           make_index_sequence<tuple_size<T1>::value>{},
                           make_index_sequence<tuple_size<T2>::value>{},
                           make_index_sequence<tuple_size<T3>::value>{});
}

template <class T0, class T1, class T2, class T3, class T4>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1, T2 const& t2, T3 const& t3, T4 const& t4)
{
  return detail::tuple_cat(t0, t1, t2, t3, t4,
                           make_index_sequence<tuple_size<T0>::value>{},
                           make_index_sequence<tuple_size<T1>::value>{},
                           make_index_sequence<tuple_size<T2>::value>{},
                           make_index_sequence<tuple_size<T3>::value>{},
                           make_index_sequence<tuple_size<T4>::value>{});
}

template <class T0, class T1, class T2, class T3, class T4, class T5, class... Ts>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1, T2 const& t2, T3 const& t3, T4 const& t4, T5 const& t5, Ts const&... ts)
{
  return cute::tuple_cat(cute::tuple_cat(t0,t1,t2,t3,t4), t5, ts...);
}
#endif

#if 0
// Outer-Inner indexing trick to concat all tuples at once

namespace detail {

template <size_t... Ns>
struct tuple_cat_helper
{
  static constexpr cute::array<size_t,sizeof...(Ns)> ns = {Ns...};

  static constexpr size_t total_size() {
    size_t sum = 0;
    for (size_t n : ns) sum += n;
    return sum;
  }
  static constexpr size_t total_size_ = total_size();

  static constexpr auto values() {
    cute::array<size_t[2],total_size_> outer_inner = {};

    size_t idx = 0;
    for (size_t i = 0; i < ns.size(); ++i) {
      for (size_t j = 0; j < ns[i]; ++j, ++idx) {
        outer_inner[idx][0] = i;
        outer_inner[idx][1] = j;
      }
    }
    return outer_inner;
  }
  static constexpr auto outer_inner_ = values();

  using total_sequence = make_index_sequence<total_size_>;
};

template <class Helper, class Tuple, size_t... I>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(Tuple const& t, index_sequence<I...>)
{
  return cute::make_tuple(get<Helper::outer_inner_[I][1]>(get<Helper::outer_inner_[I][0]>(t))...);
}

template <class T0, class T1,
          size_t... I0, size_t... I1>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1,
          index_sequence<I0...>, index_sequence<I1...>)
{
  return cute::make_tuple(get<I0>(t0)..., get<I1>(t1)...);
}

} // end namespace detail

CUTE_HOST_DEVICE constexpr
tuple<>
tuple_cat()
{
  return {};
}

template <class Tuple,
          __CUTE_REQUIRES(is_tuple<Tuple>::value)>
CUTE_HOST_DEVICE constexpr
Tuple const&
tuple_cat(Tuple const& t)
{
  return t;
}

template <class T0, class T1>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(T0 const& t0, T1 const& t1)
{
  return detail::tuple_cat(t0, t1,
                           make_index_sequence<tuple_size<T0>::value>{},
                           make_index_sequence<tuple_size<T1>::value>{});
}

template <class... Tuples>
CUTE_HOST_DEVICE constexpr
auto
tuple_cat(Tuples const&... ts)
{
  using Helper = detail::tuple_cat_helper<tuple_size<Tuples>::value...>;
  return detail::tuple_cat<Helper>(cute::make_tuple(ts...), typename Helper::total_sequence{});
}
#endif

//
// Equality operators
//

namespace detail {

template <size_t I, class TupleA, class TupleB>
CUTE_HOST_DEVICE constexpr
auto
equal_impl(TupleA const& a, TupleB const& b)
{
  if constexpr (I == tuple_size<TupleA>::value) {
    return cute::true_type{};   // Terminal: TupleA is exhausted
  } else if constexpr (I == tuple_size<TupleB>::value) {
    return cute::false_type{};  // Terminal: TupleA is not exhausted, TupleB is exhausted
  } else {
    return (get<I>(a) == get<I>(b)) && equal_impl<I+1>(a,b);
  }

  CUTE_GCC_UNREACHABLE;
}

} // end namespace detail

template <class TupleT, class TupleU,
          __CUTE_REQUIRES(is_tuple<TupleT>::value && is_tuple<TupleU>::value)>
CUTE_HOST_DEVICE constexpr
auto
operator==(TupleT const& t, TupleU const& u)
{
  return detail::equal_impl<0>(t, u);
}

template <class TupleT, class TupleU,
          __CUTE_REQUIRES(is_tuple<TupleT>::value ^ is_tuple<TupleU>::value)>
CUTE_HOST_DEVICE constexpr
auto
operator==(TupleT const& t, TupleU const& u)
{
  return cute::false_type{};
}

template <class TupleT, class TupleU,
          __CUTE_REQUIRES(is_tuple<TupleT>::value && is_tuple<TupleU>::value)>
CUTE_HOST_DEVICE constexpr
auto
operator!=(TupleT const& t, TupleU const& u)
{
  return !(t == u);
}

template <class TupleT, class TupleU,
          __CUTE_REQUIRES(is_tuple<TupleT>::value ^ is_tuple<TupleU>::value)>
CUTE_HOST_DEVICE constexpr
auto
operator!=(TupleT const& t, TupleU const& u)
{
  return cute::true_type{};
}

//
// Comparison operators
//

//
// There are many ways to compare tuple of elements and because CuTe is built
//   on parameterizing layouts of coordinates, some comparisons are appropriate
//   only in certain cases.
//  -- lexicographical comparison [reverse, reflected, revref]
//  -- colexicographical comparison [reverse, reflected, revref]
//  -- element-wise comparison [any,all]
// This can be very confusing. To avoid errors in selecting the appropriate
//   comparison, op<|op<=|op>|op>= are *not* implemented for cute::tuple.
//
// That said, see int_tuple for more explicitly named common comparison ops.
//

//
// Display utilities
//

namespace detail {

template <class Tuple, size_t... Is>
CUTE_HOST_DEVICE void print_tuple(Tuple const& t,
                                  index_sequence<Is...>, char s = '(', char e = ')')
{
  using eat = int[];
  using cute::print;
  (void) eat {(print(s), 0),
              (print(Is == 0 ? "" : ","), print(get<Is>(t)), 0)...,
              (print(e), 0)};
}

#if !defined(__CUDACC_RTC__)
template <class Tuple, std::size_t... Is>
CUTE_HOST std::ostream& print_tuple_os(std::ostream& os, Tuple const& t,
                                       index_sequence<Is...>, char s = '(', char e = ')')
{
  using eat = int[];
  (void) eat {(void(os << s), 0),
              (void(os << (Is == 0 ? "" : ",") << get<Is>(t)), 0)...,
              (void(os << e), 0)};
  return os;
}
#endif // !defined(__CUDACC_RTC__)

} // end namespace detail

template <class Tuple,
          __CUTE_REQUIRES(is_tuple<Tuple>::value)>
CUTE_HOST_DEVICE void print(Tuple const& t)
{
  return detail::print_tuple(t, make_index_sequence<tuple_size<Tuple>::value>{});
}

#if !defined(__CUDACC_RTC__)
template <class Tuple,
          __CUTE_REQUIRES(is_tuple<Tuple>::value)>
CUTE_HOST std::ostream& operator<<(std::ostream& os, Tuple const& t)
{
  return detail::print_tuple_os(os, t, make_index_sequence<tuple_size<Tuple>::value>{});
}
#endif // !defined(__CUDACC_RTC__)

} // end namespace cute

namespace CUTE_STL_NAMESPACE
{

template <class... T>
struct tuple_size<cute::tuple<T...>>
    : CUTE_STL_NAMESPACE::integral_constant<size_t, sizeof...(T)>
{};

template <size_t I, class... T>
struct tuple_element<I, cute::tuple<T...>>
    : CUTE_STL_NAMESPACE::tuple_element<I, CUTE_STL_NAMESPACE::tuple<T...>>
{};

template <class... T>
struct tuple_size<const cute::tuple<T...>>
    : CUTE_STL_NAMESPACE::integral_constant<size_t, sizeof...(T)>
{};

template <size_t I, class... T>
struct tuple_element<I, const cute::tuple<T...>>
    : CUTE_STL_NAMESPACE::tuple_element<I, const CUTE_STL_NAMESPACE::tuple<T...>>
{};

} // end namespace CUTE_STL_NAMESPACE

//
// std compatibility
//

#ifdef CUTE_STL_NAMESPACE_IS_CUDA_STD
namespace std
{

#if defined(__CUDACC_RTC__)
template <class... _Tp>
struct tuple_size;

template<size_t _Ip, class... _Tp>
struct tuple_element;
#endif

template <class... T>
struct tuple_size<cute::tuple<T...>>
    : CUTE_STL_NAMESPACE::integral_constant<size_t, sizeof...(T)>
{};

template <size_t I, class... T>
struct tuple_element<I, cute::tuple<T...>>
    : CUTE_STL_NAMESPACE::tuple_element<I, CUTE_STL_NAMESPACE::tuple<T...>>
{};

template <class... T>
struct tuple_size<const cute::tuple<T...>>
    : CUTE_STL_NAMESPACE::integral_constant<size_t, sizeof...(T)>
{};

template <size_t I, class... T>
struct tuple_element<I, const cute::tuple<T...>>
    : CUTE_STL_NAMESPACE::tuple_element<I, const CUTE_STL_NAMESPACE::tuple<T...>>
{};

} // end namepsace std
#endif // CUTE_STL_NAMESPACE_IS_CUDA_STD