span.h

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#ifndef XGBOOST_SPAN_H_
#define XGBOOST_SPAN_H_
 
#include <xgboost/base.h>
 
#include <cstddef>  // size_t
#include <cstdio>
#include <iterator>
#include <limits>  // numeric_limits
#include <type_traits>
#include <utility>  // for move
#include <vector>   // for vector
 
#if defined(__CUDACC__)
#include <cuda_runtime.h>
#endif  // defined(__CUDACC__)
 
#if defined(_MSC_VER) && _MSC_VER < 1910
 
#define __span_noexcept
 
#pragma push_macro("constexpr")
#define constexpr /*constexpr*/
 
#else
 
#define __span_noexcept noexcept
 
#endif  // defined(_MSC_VER) && _MSC_VER < 1910
 
namespace xgboost::common {
 
#if defined(__CUDA_ARCH__)
// Usual logging facility is not available inside device code.
 
#if defined(_MSC_VER)
 
// Windows CUDA doesn't have __assert_fail.
#define CUDA_KERNEL_CHECK(cond)           \
  do {                                    \
    if (XGBOOST_EXPECT(!(cond), false)) { \
      asm("trap;");                       \
    }                                     \
  } while (0)
 
#else  // defined(_MSC_VER)
 
#define __ASSERT_STR_HELPER(x) #x
 
#define CUDA_KERNEL_CHECK(cond) \
  (XGBOOST_EXPECT((cond), true) \
       ? static_cast<void>(0)   \
       : __assert_fail(__ASSERT_STR_HELPER((cond)), __FILE__, __LINE__, __PRETTY_FUNCTION__))
 
#endif  // defined(_MSC_VER)
 
#define KERNEL_CHECK CUDA_KERNEL_CHECK
 
#define SPAN_CHECK KERNEL_CHECK
 
#else  // ------------------------------ not CUDA ----------------------------
 
#if defined(XGBOOST_STRICT_R_MODE) && XGBOOST_STRICT_R_MODE == 1
 
#define KERNEL_CHECK(cond)
 
#define SPAN_CHECK(cond) KERNEL_CHECK(cond)
 
#else
 
#if defined(__SYCL_DEVICE_ONLY__)
 
// SYCL doesn't support termination
#define SYCL_KERNEL_CHECK(cond)
 
#define KERNEL_CHECK(cond) SYCL_KERNEL_CHECK(cond)
 
#else  // defined(__SYCL_DEVICE_ONLY__)
#define KERNEL_CHECK(cond) (XGBOOST_EXPECT((cond), true) ? static_cast<void>(0) : std::terminate())
#endif  // defined(__SYCL_DEVICE_ONLY__)
 
#define SPAN_CHECK(cond) KERNEL_CHECK(cond)
 
#endif  // defined(XGBOOST_STRICT_R_MODE)
 
#endif  // __CUDA_ARCH__
 
#define SPAN_LT(lhs, rhs) SPAN_CHECK((lhs) < (rhs))
 
namespace detail {
using ptrdiff_t = typename std::conditional_t<  // NOLINT
    std::is_same_v<std::ptrdiff_t, std::int64_t>, std::ptrdiff_t, std::int64_t>;
}  // namespace detail
 
#if defined(_MSC_VER) && _MSC_VER < 1910
constexpr const std::size_t
dynamic_extent = std::numeric_limits<std::size_t>::max();  // NOLINT
#else
constexpr std::size_t dynamic_extent = std::numeric_limits<std::size_t>::max();  // NOLINT
#endif  // defined(_MSC_VER) && _MSC_VER < 1910
 
enum class byte : unsigned char {};  // NOLINT
 
template <class ElementType, std::size_t Extent>
class Span;
 
namespace detail {
 
template <typename SpanType, bool IsConst>
class SpanIterator {
  using ElementType = typename SpanType::element_type;
 
 public:
  using iterator_category = std::random_access_iterator_tag;      // NOLINT
  using value_type = typename SpanType::value_type;  // NOLINT
  using difference_type = detail::ptrdiff_t;             // NOLINT
 
  using reference = typename std::conditional<                    // NOLINT
    IsConst, const ElementType, ElementType>::type&;
  using pointer = typename std::add_pointer<reference>::type;     // NOLINT
 
  constexpr SpanIterator() = default;
 
  XGBOOST_DEVICE constexpr SpanIterator(
      const SpanType* _span,
      typename SpanType::index_type _idx) __span_noexcept :
                                           span_(_span), index_(_idx) {}
 
  friend SpanIterator<SpanType, true>;
  template <bool B, typename std::enable_if_t<!B && IsConst>* = nullptr>
  XGBOOST_DEVICE constexpr SpanIterator(  // NOLINT
      const SpanIterator<SpanType, B>& other_) __span_noexcept
      : SpanIterator(other_.span_, other_.index_) {}
 
  XGBOOST_DEVICE reference operator*() const {
    SPAN_CHECK(index_ < span_->size());
    return *(span_->data() + index_);
  }
  XGBOOST_DEVICE reference operator[](difference_type n) const {
    return *(*this + n);
  }
 
  XGBOOST_DEVICE pointer operator->() const {
    SPAN_CHECK(index_ != span_->size());
    return span_->data() + index_;
  }
 
  XGBOOST_DEVICE SpanIterator& operator++() {
    SPAN_CHECK(index_ != span_->size());
    index_++;
    return *this;
  }
 
  XGBOOST_DEVICE SpanIterator operator++(int) {
    auto ret = *this;
    ++(*this);
    return ret;
  }
 
  XGBOOST_DEVICE SpanIterator& operator--() {
    SPAN_CHECK(index_ != 0 && index_ <= span_->size());
    index_--;
    return *this;
  }
 
  XGBOOST_DEVICE SpanIterator operator--(int) {
    auto ret = *this;
    --(*this);
    return ret;
  }
 
  XGBOOST_DEVICE SpanIterator operator+(difference_type n) const {
    auto ret = *this;
    return ret += n;
  }
 
  XGBOOST_DEVICE SpanIterator& operator+=(difference_type n) {
    SPAN_CHECK((index_ + n) <= span_->size());
    index_ += n;
    return *this;
  }
 
  XGBOOST_DEVICE difference_type operator-(SpanIterator rhs) const {
    SPAN_CHECK(span_ == rhs.span_);
    return index_ - rhs.index_;
  }
 
  XGBOOST_DEVICE SpanIterator operator-(difference_type n) const {
    auto ret = *this;
    return ret -= n;
  }
 
  XGBOOST_DEVICE SpanIterator& operator-=(difference_type n) {
    return *this += -n;
  }
 
  // friends
  XGBOOST_DEVICE constexpr friend bool operator==(
      SpanIterator _lhs, SpanIterator _rhs) __span_noexcept {
    return _lhs.span_ == _rhs.span_ && _lhs.index_ == _rhs.index_;
  }
 
  XGBOOST_DEVICE constexpr friend bool operator!=(
      SpanIterator _lhs, SpanIterator _rhs) __span_noexcept {
    return !(_lhs == _rhs);
  }
 
  XGBOOST_DEVICE constexpr friend bool operator<(
      SpanIterator _lhs, SpanIterator _rhs) __span_noexcept {
    return _lhs.index_ < _rhs.index_;
  }
 
  XGBOOST_DEVICE constexpr friend bool operator<=(
      SpanIterator _lhs, SpanIterator _rhs) __span_noexcept {
    return !(_rhs < _lhs);
  }
 
  XGBOOST_DEVICE constexpr friend bool operator>(
      SpanIterator _lhs, SpanIterator _rhs) __span_noexcept {
    return _rhs < _lhs;
  }
 
  XGBOOST_DEVICE constexpr friend bool operator>=(
      SpanIterator _lhs, SpanIterator _rhs) __span_noexcept {
    return !(_rhs > _lhs);
  }
 
 protected:
  const SpanType *span_ { nullptr };
  typename SpanType::index_type index_ { 0 };
};
 
 
// It's tempting to use constexpr instead of structs to do the following meta
// programming. But remember that we are supporting MSVC 2013 here.
 
template <std::size_t Extent, std::size_t Offset, std::size_t Count>
struct ExtentValue : public std::integral_constant<
  std::size_t, Count != dynamic_extent ?
  Count : (Extent != dynamic_extent ? Extent - Offset : Extent)> {};
 
template <typename T, std::size_t Extent>
struct ExtentAsBytesValue : public std::integral_constant<
  std::size_t,
  Extent == dynamic_extent ?
  Extent : sizeof(T) * Extent> {};
 
template <std::size_t From, std::size_t To>
struct IsAllowedExtentConversion : public std::integral_constant<
  bool, From == To || From == dynamic_extent || To == dynamic_extent> {};
 
template <class From, class To>
struct IsAllowedElementTypeConversion
    : public std::integral_constant<bool, std::is_convertible_v<From (*)[], To (*)[]>> {}; // NOLINT
 
template <class T>
struct IsSpanOracle : std::false_type {};
 
template <class T, std::size_t Extent>
struct IsSpanOracle<Span<T, Extent>> : std::true_type {};
 
template <class T>
struct IsSpan : public IsSpanOracle<typename std::remove_cv_t<T>> {};
 
// Re-implement std algorithms here to adopt CUDA.
template <typename T>
struct Less {
  XGBOOST_DEVICE constexpr bool operator()(const T& _x, const T& _y) const {
    return _x < _y;
  }
};
 
template <typename T>
struct Greater {
  XGBOOST_DEVICE constexpr bool operator()(const T& _x, const T& _y) const {
    return _x > _y;
  }
};
 
template <class InputIt1, class InputIt2,
          class Compare =
          detail::Less<decltype(std::declval<InputIt1>().operator*())>>
XGBOOST_DEVICE bool LexicographicalCompare(InputIt1 first1, InputIt1 last1,
                                            InputIt2 first2, InputIt2 last2) {
  Compare comp;
  for (; first1 != last1 && first2 != last2; ++first1, ++first2) {
    if (comp(*first1, *first2)) {
      return true;
    }
    if (comp(*first2, *first1)) {
      return false;
    }
  }
  return first1 == last1 && first2 != last2;
}
 
}  // namespace detail
 
template <typename T>
XGBOOST_DEVICE std::enable_if_t<!std::is_reference_v<T>, std::size_t> SizeBytes(std::size_t n) {
  return n * sizeof(T);
}
 
template <typename T,
          std::size_t Extent = dynamic_extent>
class Span {
 public:
  using element_type = T;                               // NOLINT
  using value_type = typename std::remove_cv<T>::type;  // NOLINT
  using index_type = std::size_t;                       // NOLINT
  using difference_type = detail::ptrdiff_t;            // NOLINT
  using pointer = T*;                                   // NOLINT
  using reference = T&;                                 // NOLINT
 
  using iterator = detail::SpanIterator<Span<T, Extent>, false>;               // NOLINT
  using const_iterator = const detail::SpanIterator<Span<T, Extent>, true>;    // NOLINT
  using reverse_iterator = std::reverse_iterator<iterator>;                    // NOLINT
  using const_reverse_iterator = const std::reverse_iterator<const_iterator>;  // NOLINT
 
  // constructors
  constexpr Span() = default;
 
  XGBOOST_DEVICE Span(pointer _ptr, index_type _count) :
      size_(_count), data_(_ptr) {
    SPAN_CHECK(!(Extent != dynamic_extent && _count != Extent));
    SPAN_CHECK(_ptr || _count == 0);
  }
 
  XGBOOST_DEVICE Span(pointer _first, pointer _last) :
      size_(_last - _first), data_(_first) {
    SPAN_CHECK(data_ || size_ == 0);
  }
 
  template <std::size_t N>
  XGBOOST_DEVICE constexpr Span(element_type (&arr)[N])  // NOLINT
      __span_noexcept : size_(N), data_(&arr[0]) {}
 
  template <class Container,
            class = typename std::enable_if_t<
                !std::is_const_v<element_type> && !detail::IsSpan<Container>::value &&
                std::is_convertible_v<typename Container::pointer, pointer> &&
                std::is_convertible_v<typename Container::pointer,
                                      decltype(std::declval<Container>().data())>>>
  Span(Container& _cont)  // NOLINT
      : size_(_cont.size()), data_(_cont.data()) {
    static_assert(!detail::IsSpan<Container>::value, "Wrong constructor of Span is called.");
  }
 
  template <class Container,
            class = typename std::enable_if_t<
                std::is_const_v<element_type> && !detail::IsSpan<Container>::value &&
                std::is_convertible_v<typename Container::pointer, pointer> &&
                std::is_convertible_v<typename Container::pointer,
                                      decltype(std::declval<Container>().data())>>>
  Span(const Container& _cont)  // NOLINT
      : size_(_cont.size()), data_(_cont.data()) {
    static_assert(!detail::IsSpan<Container>::value, "Wrong constructor of Span is called.");
  }
 
  template <class U, std::size_t OtherExtent,
            class = typename std::enable_if_t<
                detail::IsAllowedElementTypeConversion<U, T>::value &&
                detail::IsAllowedExtentConversion<OtherExtent, Extent>::value>>
  XGBOOST_DEVICE constexpr Span(const Span<U, OtherExtent>& _other)  // NOLINT
      __span_noexcept : size_(_other.size()),
                        data_(_other.data()) {}
 
  constexpr Span(Span const& _other) noexcept(true) = default;
  constexpr Span& operator=(Span const& _other) noexcept(true) = default;
  constexpr Span(Span&& _other) noexcept(true) = default;
  constexpr Span& operator=(Span&& _other) noexcept(true) = default;
  ~Span() noexcept(true) = default;
 
  XGBOOST_DEVICE constexpr iterator begin() const __span_noexcept {  // NOLINT
    return {this, 0};
  }
 
  XGBOOST_DEVICE constexpr iterator end() const __span_noexcept {    // NOLINT
    return {this, size()};
  }
 
  XGBOOST_DEVICE constexpr const_iterator cbegin() const __span_noexcept {  // NOLINT
    return {this, 0};
  }
 
  XGBOOST_DEVICE constexpr const_iterator cend() const __span_noexcept {    // NOLINT
    return {this, size()};
  }
 
  constexpr reverse_iterator rbegin() const __span_noexcept {  // NOLINT
    return reverse_iterator{end()};
  }
 
  constexpr reverse_iterator rend() const __span_noexcept {  // NOLINT
    return reverse_iterator{begin()};
  }
 
  XGBOOST_DEVICE constexpr const_reverse_iterator crbegin() const __span_noexcept {  // NOLINT
    return const_reverse_iterator{cend()};
  }
 
  XGBOOST_DEVICE constexpr const_reverse_iterator crend() const __span_noexcept {    // NOLINT
    return const_reverse_iterator{cbegin()};
  }
 
  // element access
 
  XGBOOST_DEVICE reference front() const {  // NOLINT
    return (*this)[0];
  }
 
  XGBOOST_DEVICE reference back() const {  // NOLINT
    return (*this)[size() - 1];
  }
 
  XGBOOST_DEVICE reference operator[](index_type _idx) const {
    SPAN_LT(_idx, size());
    return data()[_idx];
  }
 
  XGBOOST_DEVICE reference operator()(index_type _idx) const {
    return this->operator[](_idx);
  }
 
  XGBOOST_DEVICE constexpr pointer data() const __span_noexcept {   // NOLINT
    return data_;
  }
 
  // Observers
  XGBOOST_DEVICE constexpr index_type size() const __span_noexcept {  // NOLINT
    return size_;
  }
  XGBOOST_DEVICE constexpr index_type size_bytes() const __span_noexcept {  // NOLINT
    return SizeBytes<T>(size());
  }
 
  XGBOOST_DEVICE constexpr bool empty() const __span_noexcept {  // NOLINT
    return size() == 0;
  }
 
  // Subviews
  template <std::size_t Count>
  XGBOOST_DEVICE Span<element_type, Count> first() const {  // NOLINT
    SPAN_CHECK(Count <= size());
    return {data(), Count};
  }
 
  XGBOOST_DEVICE Span<element_type, dynamic_extent> first(  // NOLINT
      std::size_t _count) const {
    SPAN_CHECK(_count <= size());
    return {data(), _count};
  }
 
  template <std::size_t Count>
  XGBOOST_DEVICE Span<element_type, Count> last() const {  // NOLINT
    SPAN_CHECK(Count <= size());
    return {data() + size() - Count, Count};
  }
 
  XGBOOST_DEVICE Span<element_type, dynamic_extent> last(  // NOLINT
      std::size_t _count) const {
    SPAN_CHECK(_count <= size());
    return subspan(size() - _count, _count);
  }
 
  template <std::size_t Offset,
            std::size_t Count = dynamic_extent>
  XGBOOST_DEVICE auto subspan() const ->                   // NOLINT
      Span<element_type,
           detail::ExtentValue<Extent, Offset, Count>::value> {
    SPAN_CHECK((Count == dynamic_extent) ?
               (Offset <= size()) : (Offset + Count <= size()));
    return {data() + Offset, Count == dynamic_extent ? size() - Offset : Count};
  }
 
  XGBOOST_DEVICE Span<element_type, dynamic_extent> subspan(  // NOLINT
      index_type _offset,
      index_type _count = dynamic_extent) const {
    SPAN_CHECK((_count == dynamic_extent) ?
               (_offset <= size()) : (_offset + _count <= size()));
    return {data() + _offset, _count ==
            dynamic_extent ? size() - _offset : _count};
  }
 
 private:
  index_type size_ { 0 };
  pointer data_ { nullptr };
};
 
template <class T, std::size_t X, class U, std::size_t Y>
XGBOOST_DEVICE bool operator==(Span<T, X> l, Span<U, Y> r) {
  if (l.size() != r.size()) {
    return false;
  }
  for (auto l_beg = l.cbegin(), r_beg = r.cbegin(); l_beg != l.cend();
       ++l_beg, ++r_beg) {
    if (*l_beg != *r_beg) {
      return false;
    }
  }
  return true;
}
 
template <class T, std::size_t X, class U, std::size_t Y>
XGBOOST_DEVICE constexpr bool operator!=(Span<T, X> l, Span<U, Y> r) {
  return !(l == r);
}
 
template <class T, std::size_t X, class U, std::size_t Y>
XGBOOST_DEVICE constexpr bool operator<(Span<T, X> l, Span<U, Y> r) {
  return detail::LexicographicalCompare(l.begin(), l.end(),
                                         r.begin(), r.end());
}
 
template <class T, std::size_t X, class U, std::size_t Y>
XGBOOST_DEVICE constexpr bool operator<=(Span<T, X> l, Span<U, Y> r) {
  return !(l > r);
}
 
template <class T, std::size_t X, class U, std::size_t Y>
XGBOOST_DEVICE constexpr bool operator>(Span<T, X> l, Span<U, Y> r) {
  return detail::LexicographicalCompare<
    typename Span<T, X>::iterator, typename Span<U, Y>::iterator,
    detail::Greater<typename Span<T, X>::element_type>>(l.begin(), l.end(),
                                                        r.begin(), r.end());
}
 
template <class T, std::size_t X, class U, std::size_t Y>
XGBOOST_DEVICE constexpr bool operator>=(Span<T, X> l, Span<U, Y> r) {
  return !(l < r);
}
 
template <class T, std::size_t E>
XGBOOST_DEVICE auto as_bytes(Span<T, E> s) __span_noexcept ->           // NOLINT
    Span<const byte, detail::ExtentAsBytesValue<T, E>::value> {
  return {reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
}
 
template <class T, std::size_t E>
XGBOOST_DEVICE auto as_writable_bytes(Span<T, E> s) __span_noexcept ->  // NOLINT
    Span<byte, detail::ExtentAsBytesValue<T, E>::value> {
  return {reinterpret_cast<byte*>(s.data()), s.size_bytes()};
}
 
template <typename It>
class IterSpan {
 public:
  using value_type = typename std::iterator_traits<It>::value_type;  // NOLINT
  using index_type = std::size_t;                                    // NOLINT
  using iterator = It;                                               // NOLINT
 
 private:
  It it_;
  index_type size_{0};
 
 public:
  IterSpan() = default;
  XGBOOST_DEVICE IterSpan(It it, index_type size) : it_{std::move(it)}, size_{size} {}
  XGBOOST_DEVICE explicit IterSpan(common::Span<It, dynamic_extent> span)
      : it_{span.data()}, size_{span.size()} {}
 
  [[nodiscard]] XGBOOST_DEVICE index_type size() const noexcept { return size_; }  // NOLINT
  [[nodiscard]] XGBOOST_DEVICE decltype(auto) operator[](index_type i) const { return it_[i]; }
  [[nodiscard]] XGBOOST_DEVICE decltype(auto) operator[](index_type i) { return it_[i]; }
  [[nodiscard]] XGBOOST_DEVICE bool empty() const noexcept { return size() == 0; }  // NOLINT
  [[nodiscard]] XGBOOST_DEVICE It data() const noexcept { return it_; }             // NOLINT
  [[nodiscard]] XGBOOST_DEVICE IterSpan<It> subspan(                                // NOLINT
      index_type _offset, index_type _count = dynamic_extent) const {
    SPAN_CHECK((_count == dynamic_extent) ? (_offset <= size()) : (_offset + _count <= size()));
    return {data() + _offset, _count == dynamic_extent ? size() - _offset : _count};
  }
  [[nodiscard]] XGBOOST_DEVICE constexpr iterator begin() const noexcept {  // NOLINT
    return it_;
  }
  [[nodiscard]] XGBOOST_DEVICE constexpr iterator end() const noexcept {  // NOLINT
    return it_ + size();
  }
};
 
template <typename T>
Span(std::vector<T> const&) -> Span<T const>;
 
template <typename T>
Span(std::vector<T>&) -> Span<T>;
}  // namespace xgboost::common
 
 
#if defined(_MSC_VER) &&_MSC_VER < 1910
#undef constexpr
#pragma pop_macro("constexpr")
#undef __span_noexcept
#endif  // _MSC_VER < 1910
 
#endif  // XGBOOST_SPAN_H_