span.icc

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/*
 * Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration.
 */
/**
 * @file CxxUtils/span.icc
 * @author scott snyder <snyder@bnl.gov>
 * @date Jan, 2022
 * @brief Simplified version of the C++20 std::span.
 */
 
 
namespace CxxUtils {
 
 
/*
 * @brief Default constructor.
 * Makes an empty span.
 */
template <class T>
inline
span<T>::span()
  : m_ptr(nullptr),
    m_size(0)
{
}
 
 
/**
  * @brief Constructor from start and length.
  * @param ptr Start of the span.
  * @param sz Length of the span.
  */
template <class T>
#if HAVE_CONCEPTS
template <class U>
requires (valid_span_type_v<T, U>)
#else
template <class U, typename>
#endif
inline
span<T>::span (U* ptr, size_type sz)
  : m_ptr (ptr),
    m_size (sz)
{
  // cppcheck-suppress missingReturn; false positive
}
 
 
/**
  * @brief Constructor from start and end.
  * @param beg Start of the span.
  * @param end One past the end of the span.
  */
template <class T>
#if HAVE_CONCEPTS
template <class U>
requires (valid_span_type_v<T, U>)
#else
template <class U, typename>
#endif
inline
span<T>::span (U* beg, U* end)
  : m_ptr (beg),
    m_size (end-beg)
{
  // cppcheck-suppress missingReturn; false positive
}
 
 
/**
 * @brief Constructor from another span.
 * @param other Span to copy from.
  */
template <class T>
#if HAVE_CONCEPTS
template <class U>
requires (valid_span_type_v<T, U>)
#else
template <class U, typename>
#endif
inline
span<T>::span (const span<U>& other)
  : m_ptr (other.begin()),
    m_size (other.size())
{
}
 
 
/**
  * @brief Return the size of the span.
  */
template <class T>
inline
constexpr typename span<T>::size_type
span<T>::size() const noexcept
{
  return m_size;
}
 
 
/**
  * @brief Return the size of contents of the span, in bytes.
  */
template <class T>
inline
constexpr typename span<T>::size_type
span<T>::size_bytes() const noexcept
{
  return m_size * sizeof(element_type);
}
 
  
/**
  * @brief Test if the span is empty.
  */
template <class T>
inline
constexpr bool
span<T>::empty() const noexcept
{
  return m_size == 0;
}
 
 
/**
  * @brief Return a reference to the first element in the span.
  */
template <class T>
inline
constexpr typename span<T>::reference
span<T>::front() noexcept
{
  assert (m_ptr != nullptr);
  return *m_ptr;
}
 
   
/**
  * @brief Return a reference to the first element in the span.
  */
template <class T>
inline
constexpr typename span<T>::const_reference
span<T>::front() const noexcept
{
  assert (m_ptr != nullptr);
  return *m_ptr;
}
 
  
/**
  * @brief Return a reference to the last element in the span.
  */
template <class T>
inline
constexpr typename span<T>::reference
span<T>::back() noexcept
{
  assert (m_ptr != nullptr);
  return *(m_ptr + m_size-1);
}
 
  
/**
  * @brief Return a reference to the last element in the span.
  */
template <class T>
inline
constexpr typename span<T>::const_reference
span<T>::back() const noexcept
{
  assert (m_ptr != nullptr);
  return *(m_ptr + m_size-1);
}
 
  
/**
  * @brief Return a reference to the i-th element in the span.
  * @param i Index of the element to return.
  */
template <class T>
inline
constexpr typename span<T>::reference
span<T>::operator[] (size_type i) noexcept
{
  assert (i < m_size);
  return m_ptr[i];
}
 
  
/**
  * @brief Return a reference to the i-th element in the span.
  * @param i Index of the element to return.
  */
template <class T>
inline
constexpr typename span<T>::const_reference
span<T>::operator[] (size_type i) const noexcept
{
  assert (i < m_size);
  return m_ptr[i];
}
 
 
/**
  * @brief Return a reference to the i-th element in the span (bounds-checked).
  * @param i Index of the element to return.
  */
template <class T>
inline
constexpr typename span<T>::reference
span<T>::at (size_type i)
{
  if (i >= m_size) throw std::out_of_range ("CxxUtils::span::at");
  return m_ptr[i];
}
 
 
/**
  * @brief Return a reference to the i-th element in the span (bounds-checked).
  * @param i Index of the element to return.
  */
template <class T>
inline
constexpr typename span<T>::const_reference
span<T>::at (size_type i) const
{
  if (i >= m_size) throw std::out_of_range ("CxxUtils::span::at");
  return m_ptr[i];
}
 
 
/**
  * @brief Return a pointer to the start of the span.
  */
template <class T>
inline
constexpr typename span<T>::pointer
span<T>::data() noexcept
{
  return m_ptr;
}
 
  
/**
  * @brief Return a pointer to the start of the span.
  */
template <class T>
inline
constexpr typename span<T>::const_pointer
span<T>::data() const noexcept
{
  return m_ptr;
}
 
 
/**
  * @brief Return a begin iterator.
  */
template <class T>
inline
constexpr typename span<T>::iterator
span<T>::begin() noexcept
{
  return m_ptr;
}
 
  
/**
  * @brief Return a begin iterator.
  */
template <class T>
inline
constexpr typename span<T>::const_iterator
span<T>::begin() const noexcept
{
  return m_ptr;
} 
 
 
/**
  * @brief Return an end iterator.
  */
template <class T>
inline
constexpr typename span<T>::iterator
span<T>::end() noexcept
{
  return m_ptr + m_size;
}
 
  
/**
  * @brief Return an end iterator.
  */
template <class T>
inline
constexpr typename span<T>::const_iterator
span<T>::end() const noexcept
{
  return m_ptr + m_size;
}
 
 
/**
  * @brief Return a begin reverse iterator.
  */
template <class T>
inline
constexpr typename span<T>::reverse_iterator
span<T>::rbegin() noexcept
{
  return reverse_iterator (end());
}
 
  
/**
  * @brief Return a begin reverse iterator.
  */
template <class T>
inline
constexpr typename span<T>::const_reverse_iterator
span<T>::rbegin() const noexcept
{
  return const_reverse_iterator (end());
}
 
 
/**
  * @brief Return an end reverse iterator.
  */
template <class T>
inline
constexpr typename span<T>::reverse_iterator
span<T>::rend() noexcept
{
  return reverse_iterator (begin());
}
 
 
/**
  * @brief Return an end reverse iterator.
  */
template <class T>
inline
constexpr typename span<T>::const_reverse_iterator
span<T>::rend() const noexcept
{
  return const_reverse_iterator (begin());
}
 
 
/**
  * @brief Return a subspan from the start.
  * @param n Number of elements in the subspan.
  */
template <class T>
inline
constexpr span<T>
span<T>::first (size_type n) noexcept
{
  assert (n <= size());
  return span (m_ptr, n);
}
 
  
/**
  * @brief Return a subspan from the start.
  * @param n Number of elements in the subspan.
  */
template <class T>
inline
constexpr span<const T>
span<T>::first (size_type n) const noexcept
{
  assert (n <= size());
  const T* ptr = m_ptr;
  return span<const T> (ptr, n);
}
 
 
/**
  * @brief Return a subspan from the end.
  * @param n Number of elements in the subspan.
  */
template <class T>
inline
constexpr span<T>
span<T>::last (size_type n) noexcept
{
  assert (n <= size());
  return span (m_ptr + (size() - n), n);
}
 
  
/**
  * @brief Return a subspan from the end.
  * @param n Number of elements in the subspan.
  */
template <class T>
inline
constexpr span<const T>
span<T>::last (size_type n) const noexcept
{
  assert (n <= size());
  const T* ptr = m_ptr;
  return span<const T> (ptr + (size() - n), n);
}
 
 
/**
  * @brief Return a subspan.
  * @param offs Starting element of the subspan.
  * @param n Number of elements in the subspan.
  *          If defaulted, take all remaining elements.
  */
template <class T>
inline
constexpr span<T>
span<T>::subspan (size_type offs, size_type n /*= dynamic_extent*/) noexcept
{
  assert (offs <= size());
  if (n == dynamic_extent)
    n = size() - offs;
  else {
    assert (n <= size());
    assert (offs + n <= size());
  }
  return span (m_ptr + offs, n);
}
 
 
/**
  * @brief Return a subspan.
  * @param offs Starting element of the subspan.
  * @param n Number of elements in the subspan.
  *          If defaulted, take all remaining elements.
  */
template <class T>
inline
constexpr span<const T>
span<T>::subspan (size_type offs, size_type n /*= dynamic_extent*/) const noexcept
{
  assert (offs <= size());
  if (n == dynamic_extent)
    n = size() - offs;
  else {
    assert (n <= size());
    assert (offs + n <= size());
  }
  const T* ptr = m_ptr;
  return span<const T> (ptr + offs, n);
}
 
 
} // namespace CxxUtils