//===-- lib/Evaluate/host.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
//
//===----------------------------------------------------------------------===//

#ifndef FORTRAN_EVALUATE_HOST_H_
#define FORTRAN_EVALUATE_HOST_H_

// Define a compile-time mapping between Fortran intrinsic types and host
// hardware types if possible. The purpose is to avoid having to do any kind of
// assumption on whether a "float" matches the Scalar<Type<TypeCategory::Real,
// 4>> outside of this header. The main tools are HostTypeExists<T> and
// HostType<T>. HostTypeExists<T>() will return true if and only if a host
// hardware type maps to Fortran intrinsic type T. Then HostType<T> can be used
// to safely refer to this hardware type.

#include "flang/Evaluate/type.h"
#include <cfenv>
#include <complex>
#include <cstdint>
#include <limits>
#include <string>
#include <type_traits>

namespace Fortran::evaluate {
namespace host {

// Helper class to handle host runtime traps, status flag and errno
class HostFloatingPointEnvironment {
public:
  void SetUpHostFloatingPointEnvironment(FoldingContext &);
  void CheckAndRestoreFloatingPointEnvironment(FoldingContext &);
  bool hasSubnormalFlushingHardwareControl() const {
    return hasSubnormalFlushingHardwareControl_;
  }
  void SetFlag(RealFlag flag) { flags_.set(flag); }
  bool hardwareFlagsAreReliable() const { return hardwareFlagsAreReliable_; }

private:
  std::fenv_t originalFenv_;
#if __x86_64__
  unsigned int originalMxcsr;
#endif
  RealFlags flags_;
  bool hasSubnormalFlushingHardwareControl_{false};
  bool hardwareFlagsAreReliable_{true};
};

// Type mapping from F18 types to host types
struct UnsupportedType {}; // There is no host type for the F18 type

template <typename FTN_T> struct HostTypeHelper {
  using Type = UnsupportedType;
};
template <typename FTN_T> using HostType = typename HostTypeHelper<FTN_T>::Type;

template <typename... T> constexpr inline bool HostTypeExists() {
  return (... && (!std::is_same_v<HostType<T>, UnsupportedType>));
}

// Type mapping from host types to F18 types FortranType<HOST_T> is defined
// after all HosTypeHelper definition because it reverses them to avoid
// duplication.

// Scalar conversion utilities from host scalars to F18 scalars
template <typename FTN_T>
inline constexpr Scalar<FTN_T> CastHostToFortran(const HostType<FTN_T> &x) {
  static_assert(HostTypeExists<FTN_T>());
  if constexpr (FTN_T::category == TypeCategory::Complex &&
      sizeof(Scalar<FTN_T>) != sizeof(HostType<FTN_T>)) {
    // X87 is usually padded to 12 or 16bytes. Need to cast piecewise for
    // complex
    return Scalar<FTN_T>{CastHostToFortran<typename FTN_T::Part>(std::real(x)),
        CastHostToFortran<typename FTN_T::Part>(std::imag(x))};
  } else {
    return *reinterpret_cast<const Scalar<FTN_T> *>(&x);
  }
}

// Scalar conversion utilities from F18 scalars to host scalars.
template <typename FTN_T>
inline constexpr HostType<FTN_T> CastFortranToHost(const Scalar<FTN_T> &x) {
  static_assert(HostTypeExists<FTN_T>());
  if constexpr (FTN_T::category == TypeCategory::Complex) {
    using FortranPartType = typename FTN_T::Part;
    return HostType<FTN_T>{CastFortranToHost<FortranPartType>(x.REAL()),
        CastFortranToHost<FortranPartType>(x.AIMAG())};
  } else if constexpr (std::is_same_v<FTN_T, Type<TypeCategory::Real, 10>>) {
    // x87 80-bit floating-point occupies 16 bytes as a C "long double";
    // copy the data to avoid a legitimate (but benign due to little-endianness)
    // warning from GCC >= 11.2.0.
    HostType<FTN_T> y;
    std::memcpy(&y, &x, sizeof x);
    return y;
  } else {
    static_assert(sizeof x == sizeof(HostType<FTN_T>));
    return *reinterpret_cast<const HostType<FTN_T> *>(&x);
  }
}

template <> struct HostTypeHelper<Type<TypeCategory::Integer, 1>> {
  using Type = std::int8_t;
};

template <> struct HostTypeHelper<Type<TypeCategory::Integer, 2>> {
  using Type = std::int16_t;
};

template <> struct HostTypeHelper<Type<TypeCategory::Integer, 4>> {
  using Type = std::int32_t;
};

template <> struct HostTypeHelper<Type<TypeCategory::Integer, 8>> {
  using Type = std::int64_t;
};

template <> struct HostTypeHelper<Type<TypeCategory::Integer, 16>> {
#if (defined(__GNUC__) || defined(__clang__)) && defined(__SIZEOF_INT128__)
  using Type = __int128_t;
#else
  using Type = UnsupportedType;
#endif
};

// TODO no mapping to host types are defined currently for 16bits float
// It should be defined when gcc/clang have a better support for it.

template <>
struct HostTypeHelper<
    Type<TypeCategory::Real, common::RealKindForPrecision(24)>> {
  // IEEE 754 32bits
  using Type = std::conditional_t<sizeof(float) == 4 &&
          std::numeric_limits<float>::is_iec559,
      float, UnsupportedType>;
};

template <>
struct HostTypeHelper<
    Type<TypeCategory::Real, common::RealKindForPrecision(53)>> {
  // IEEE 754 64bits
  using Type = std::conditional_t<sizeof(double) == 8 &&
          std::numeric_limits<double>::is_iec559,
      double, UnsupportedType>;
};

template <>
struct HostTypeHelper<
    Type<TypeCategory::Real, common::RealKindForPrecision(64)>> {
  // X87 80bits
  using Type = std::conditional_t<sizeof(long double) >= 10 &&
          std::numeric_limits<long double>::digits == 64 &&
          std::numeric_limits<long double>::max_exponent == 16384,
      long double, UnsupportedType>;
};

template <>
struct HostTypeHelper<
    Type<TypeCategory::Real, common::RealKindForPrecision(113)>> {
  // IEEE 754 128bits
  using Type = std::conditional_t<sizeof(long double) == 16 &&
          std::numeric_limits<long double>::digits == 113 &&
          std::numeric_limits<long double>::max_exponent == 16384,
      long double, UnsupportedType>;
};

template <int KIND> struct HostTypeHelper<Type<TypeCategory::Complex, KIND>> {
  using RealT = Fortran::evaluate::Type<TypeCategory::Real, KIND>;
  using Type = std::conditional_t<HostTypeExists<RealT>(),
      std::complex<HostType<RealT>>, UnsupportedType>;
};

template <int KIND> struct HostTypeHelper<Type<TypeCategory::Logical, KIND>> {
  using Type = std::conditional_t<KIND <= 8, std::uint8_t, UnsupportedType>;
};

template <int KIND> struct HostTypeHelper<Type<TypeCategory::Character, KIND>> {
  using Type =
      Scalar<typename Fortran::evaluate::Type<TypeCategory::Character, KIND>>;
};

// Type mapping from host types to F18 types. This need to be placed after all
// HostTypeHelper specializations.
template <typename T, typename... TT> struct IndexInTupleHelper {};
template <typename T, typename... TT>
struct IndexInTupleHelper<T, std::tuple<TT...>> {
  static constexpr int value{common::TypeIndex<T, TT...>};
};
struct UnknownType {}; // the host type does not match any F18 types
template <typename HOST_T> struct FortranTypeHelper {
  using HostTypeMapping =
      common::MapTemplate<HostType, AllIntrinsicTypes, std::tuple>;
  static constexpr int index{
      IndexInTupleHelper<HOST_T, HostTypeMapping>::value};
  // Both conditional types are "instantiated", so a valid type must be
  // created for invalid index even if not used.
  using Type = std::conditional_t<index >= 0,
      std::tuple_element_t<(index >= 0) ? index : 0, AllIntrinsicTypes>,
      UnknownType>;
};

template <typename HOST_T>
using FortranType = typename FortranTypeHelper<HOST_T>::Type;

template <typename... HT> constexpr inline bool FortranTypeExists() {
  return (... && (!std::is_same_v<FortranType<HT>, UnknownType>));
}

} // namespace host
} // namespace Fortran::evaluate

#endif // FORTRAN_EVALUATE_HOST_H_
