soa.h

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#ifndef _SOA_H
#define _SOA_H
 
#include <array>
#include <cstdint>
#include <initializer_list>
#include <new>
#include <type_traits>
#include <utility>
 
namespace soa {
 
template <typename T, uint8_t N> class Array;
 
template <typename T> struct Ptr;
 
template <class _ToType, class _FromType>
constexpr _ToType __bit_cast(const _FromType &__from) {
  return __builtin_bit_cast(_ToType, __from);
}
 
template <typename T> class BasePtr {
  static_assert(!std::is_volatile_v<T>, "volatile types are not supported");
  static_assert(std::is_trivial_v<T>, "non-trivial types are unsupported");
  static_assert(std::is_standard_layout_v<T>,
                "non-standard layout types are unsupported");
  static_assert(std::alignment_of_v<T> == 1, "aligned types are not supported");
 
protected:
  // Pointers to array elements are represented as an array of pointers to
  // each byte. This keeps the representation agnostic of the size of the
  // original array.
  const uint8_t *BytePtrs[sizeof(T)];
 
private:
  // Initializes the underlying bytes of the array using a tailcall recursive
  // function. LLVM is able to fully inline this recursive call, and this also
  // helps preserve the source info for the line when debugging.
  template <uint8_t N, uint8_t ByteIdx = 0>
  [[clang::always_inline]] constexpr void initBytePtrs(
      const uint8_t ByteArrays[][N], uint8_t Idx) {
    if constexpr (ByteIdx < sizeof(T)) {
      BytePtrs[ByteIdx] = &ByteArrays[ByteIdx][Idx];
      initBytePtrs<N, ByteIdx + 1>(ByteArrays, Idx);
    }
  }
 
public:
  template <uint8_t N>
  [[clang::always_inline]] constexpr BasePtr(const uint8_t ByteArrays[][N],
                                             uint8_t Idx) {
    initBytePtrs<N>(ByteArrays, Idx);
  }
 
  template <uint8_t N>
  [[clang::always_inline]] constexpr BasePtr(uint8_t ByteArrays[][N],
                                             uint8_t Idx) {
    initBytePtrs<N>(ByteArrays, Idx);
  }
 
  [[clang::always_inline]] T get() const { return static_cast<T>(*this); }
 
private:
  // Helper function to read the bytes using another tailcall recursive
  // function. Stores the bytes read into the array passed in as a parameter.
  template <uint8_t Idx = 0>
  [[clang::always_inline]] constexpr void readBytes(
      uint8_t (&Bytes)[sizeof(T)]) const {
    if constexpr (Idx < sizeof(T)) {
      Bytes[Idx] = *BytePtrs[Idx];
      readBytes<Idx + 1>(Bytes);
    }
  }
 
public:
  [[clang::always_inline]] constexpr operator T() const {
    uint8_t Bytes[sizeof(T)];
    readBytes(Bytes);
    return __bit_cast<T>(Bytes);
  }
 
  template <typename... ArgsT>
  [[clang::always_inline]] auto operator()(ArgsT &&...Args) const -> auto {
    return static_cast<const T>(get())(std::forward<ArgsT>(Args)...);
  }
 
private:
  // Helper function to write the bytes using yet another tailcall recursive
  // function. Stores the bytes read into the underlying byte array.
  template <uint8_t Idx = 0>
  [[clang::always_inline]] void writeBytes(const uint8_t *Bytes) {
    if constexpr (Idx < sizeof(T)) {
      *const_cast<uint8_t *>(BytePtrs[Idx]) = Bytes[Idx];
      writeBytes<Idx + 1>(Bytes);
    }
  }
 
public:
  template <typename Q = T>
  [[clang::always_inline]] std::enable_if_t<!std::is_const_v<Q>, const Ptr<T> &>
  operator=(const T &Val) {
    writeBytes(reinterpret_cast<const uint8_t *>(&Val));
    return *static_cast<Ptr<T> *>(this);
  }
 
  template <typename Q = T>
  [[clang::always_inline]] std::enable_if_t<std::is_pointer_v<Q>, const T>
  operator->() const {
    return *this;
  }
  template <typename Q = T>
  [[clang::always_inline]] std::enable_if_t<std::is_pointer_v<Q>, T>
  operator->() {
    return *this;
  }
 
private:
  class ConstWrapper {
    const T V;
 
  public:
    [[clang::always_inline]] ConstWrapper(const Ptr<T> &P) : V(P) {}
    [[clang::always_inline]] const T *operator->() const { return &V; }
  };
 
public:
  template <typename Q = T>
  [[clang::always_inline]] std::enable_if_t<!std::is_pointer_v<Q>, ConstWrapper>
  operator->() const {
    return *static_cast<const Ptr<T> *>(this);
  }
 
  template <typename U>
  [[clang::always_inline]] Ptr<T> &operator+=(const U &Right) {
    *this = *this + Right;
    return *static_cast<Ptr<T> *>(this);
  }
 
  template <typename U>
  [[clang::always_inline]] Ptr<T> &operator-=(const U &Right) {
    *this = *this - Right;
    return *static_cast<Ptr<T> *>(this);
  }
 
  template <typename U>
  [[clang::always_inline]] Ptr<T> &operator*=(const U &Right) {
    *this = *this * Right;
    return *static_cast<Ptr<T> *>(this);
  }
 
  template <typename U>
  [[clang::always_inline]] Ptr<T> &operator/=(const U &Right) {
    *this = *this / Right;
    return *static_cast<Ptr<T> *>(this);
  }
 
  template <typename U>
  [[clang::always_inline]] Ptr<T> &operator%=(const U &Right) {
    *this = *this % Right;
    return *static_cast<Ptr<T> *>(this);
  }
 
  template <typename U>
  [[clang::always_inline]] Ptr<T> &operator^=(const U &Right) {
    *this = *this ^ Right;
    return *static_cast<Ptr<T> *>(this);
  }
 
  template <typename U>
  [[clang::always_inline]] Ptr<T> &operator&=(const U &Right) {
    *this = *this & Right;
    return *static_cast<Ptr<T> *>(this);
  }
 
  template <typename U>
  [[clang::always_inline]] Ptr<T> &operator|=(const U &Right) {
    *this = *this | Right;
    return *static_cast<Ptr<T> *>(this);
  }
 
  template <typename U>
  [[clang::always_inline]] Ptr<T> &operator<<=(const U &Right) {
    *this = *this << Right;
    return *static_cast<Ptr<T> *>(this);
  }
 
  template <typename U>
  [[clang::always_inline]] Ptr<T> &operator>>=(const U &Right) {
    *this = *this >> Right;
    return *static_cast<Ptr<T> *>(this);
  }
 
  [[clang::always_inline]] Ptr<T> &operator++() {
    *this += 1;
    return *static_cast<Ptr<T> *>(this);
  }
  [[clang::always_inline]] Ptr<T> &operator--() {
    *this -= 1;
    return *static_cast<Ptr<T> *>(this);
  }
 
  [[clang::always_inline]] T operator++(int) {
    T old = *this;
    ++*this;
    return *static_cast<Ptr<T> *>(this);
  }
 
  [[clang::always_inline]] T operator--(int) {
    T old = *this;
    --*this;
    return *static_cast<Ptr<T> *>(this);
  }
};
 
template <typename T> class Ptr : public BasePtr<T> {
public:
  using BasePtr<T>::BasePtr;
  using BasePtr<T>::operator=;
};
 
template <typename T, uint8_t N> class Ptr<T[N]> {
  static_assert(!std::is_volatile_v<T>, "volatile types are not supported");
  static_assert(std::is_trivial_v<T>, "non-trivial types are unsupported");
  static_assert(std::is_standard_layout_v<T>,
                "non-standard layout types are unsupported");
  static_assert(std::alignment_of_v<T> == 1, "aligned types are not supported");
 
  uint8_t PtrStorage[sizeof(Ptr<T>[N])];
  [[clang::always_inline]] Ptr<T> *ptrs() {
    return reinterpret_cast<Ptr<T> *>(PtrStorage);
  }
 
  // Helper function to initalize the array for internal multibyte arrays
  // See also: BasePtr::initBytePtrs
  template <uint8_t M, uint8_t ArrayIdx = 0>
  [[clang::always_inline]] constexpr void initPtrs(const uint8_t ByteArrays[][M],
                                                   uint8_t Idx) {
    if constexpr (ArrayIdx < N) {
      new (&ptrs()[ArrayIdx]) Ptr<T>(ByteArrays + ArrayIdx * sizeof(T), Idx);
      initPtrs<M, ArrayIdx + 1>(ByteArrays, Idx);
    }
  }
 
public:
  template <uint8_t M>
  [[clang::always_inline]] constexpr Ptr(const uint8_t ByteArrays[][M],
                                         uint8_t Idx) {
    initPtrs<M>(ByteArrays, Idx);
  }
 
  template <uint8_t M>
  [[clang::always_inline]] constexpr Ptr(uint8_t ByteArrays[][M], uint8_t Idx) {
    initPtrs<M>(ByteArrays, Idx);
  }
 
  Ptr<const T> operator[](uint8_t Idx) const { return ptrs()[Idx]; }
  Ptr<T> operator[](uint8_t Idx) { return ptrs()[Idx]; }
};
 
template <typename T, uint8_t N> class ArrayConstIterator {
  friend class Array<T, N>;
 
protected:
  const Array<T, N> &A;
  uint8_t Idx;
 
  [[clang::always_inline]] ArrayConstIterator(const Array<T, N> &A, uint8_t Idx)
      : A(A), Idx(Idx) {}
 
public:
  [[clang::always_inline]] Ptr<const T> operator*() const { return A[Idx]; }
 
  [[clang::always_inline]] ArrayConstIterator &operator++() {
    ++Idx;
    return *this;
  }
 
  bool operator==(const ArrayConstIterator &Other) const {
    return &A == &Other.A && Idx == Other.Idx;
  }
  bool operator!=(const ArrayConstIterator &Other) const {
    return !(*this == Other);
  }
};
 
template <typename T, uint8_t N>
class ArrayIterator : public ArrayConstIterator<T, N> {
  friend class Array<T, N>;
 
  using ArrayConstIterator<T, N>::A;
  using ArrayConstIterator<T, N>::Idx;
 
  [[clang::always_inline]] ArrayIterator(Array<T, N> &A, uint8_t Idx)
      : ArrayConstIterator<T, N>(A, Idx) {}
 
public:
  [[clang::always_inline]] Ptr<T> operator*() const {
    return const_cast<soa::Array<T, N> &>(A)[Idx];
  }
 
  [[clang::always_inline]] ArrayIterator &operator++() {
    ArrayConstIterator<T, N>::operator++();
    return *this;
  }
};
 
template <typename T, uint8_t N> class Array {
  static_assert(!std::is_volatile_v<T>, "volatile types are not supported");
  static_assert(std::is_trivial_v<T>, "non-trivial types are unsupported");
  static_assert(std::is_standard_layout_v<T>,
                "only standard layout types are supported");
  static_assert(std::alignment_of_v<T> == 1, "aligned types are not supported");
 
  uint8_t ByteArrays[sizeof(T)][N];
 
  // Helper fucntion to recursively store the bytes from a multibyte array
  template <uint8_t ByteIdx = 0>
  [[clang::always_inline]] constexpr void storeEntryBytes(
      uint8_t Idx, const std::array<const uint8_t, sizeof(T)> &Bytes) {
    if constexpr (ByteIdx < sizeof(T)) {
      ByteArrays[ByteIdx][Idx] = Bytes[ByteIdx];
      storeEntryBytes<ByteIdx + 1>(Idx, Bytes);
    }
  }
 
public:
  // Note: This partially duplicates the logic in Ptr::operator=, but works for
  // types like multidimensional arrays where assignment isn't defined.
  [[clang::always_inline]] constexpr Array(std::initializer_list<T> Entries) {
    uint8_t Idx = 0;
    for (const T &Entry : Entries) {
      storeEntryBytes(Idx,
                      __bit_cast<std::array<const uint8_t, sizeof(T)>>(Entry));
      ++Idx;
    }
  }
 
  // Arrays cannot be assigned with operator= above, so provide a specific out
  // to initialize them with nested initializer lists.
  [[clang::always_inline]] constexpr Array() = default;
 
  template <uint8_t M>
  [[clang::always_inline]] constexpr Array(const Array<T, M> &Other) {
    memcpy(ByteArrays, Other.ByteArrays, sizeof(Other.ByteArrays));
  }
 
  [[clang::always_inline]] constexpr Ptr<T> operator[](uint8_t Idx) {
    return {ByteArrays, Idx};
  }
  [[clang::always_inline]] constexpr Ptr<const T>
  operator[](uint8_t Idx) const {
    return {ByteArrays, Idx};
  }
 
  [[clang::always_inline]] constexpr ArrayConstIterator<T, N> begin() const {
    return {*this, 0};
  }
  [[clang::always_inline]] constexpr ArrayConstIterator<T, N> end() const {
    return {*this, size()};
  }
 
  [[clang::always_inline]] constexpr ArrayIterator<T, N> begin() {
    return {*this, 0};
  }
  [[clang::always_inline]] constexpr ArrayIterator<T, N> end() {
    return {*this, size()};
  }
 
  [[clang::always_inline]] constexpr uint8_t size() const { return N; }
};
 
} // namespace soa
 
#endif // _SOA_H