Add span<> class template

include/ck/utility/span.hpp

+// SPDX-License-Identifier: MIT
+// Copyright (c) 2018-2022, Advanced Micro Devices, Inc. All rights reserved.
+
+#pragma once
+
+#include <cstddef>
+#include <array>
+#include <type_traits>
+
+namespace ck {
+
+template <typename T>
+class span
+{
+    public:
+    using element_type    = T;
+    using value_type      = std::remove_cv_t<element_type>;
+    using size_type       = std::size_t;
+    using difference_type = std::ptrdiff_t;
+    using pointer         = element_type*;
+    using const_pointer   = const element_type*;
+    using reference       = element_type&;
+    using const_reference = const element_type&;
+    using iterator        = pointer;
+    using const_iterator  = pointer;
+
+    constexpr span() : span(nullptr, 0) {}
+
+    constexpr span(pointer first, size_type count) : ptr_(first), size_(count) {}
+
+    constexpr span(pointer first, pointer last) : span(first, last - first) {}
+
+    template <std::size_t N>
+    constexpr span(element_type (&arr)[N]) noexcept : span(arr, N)
+    {
+    }
+
+    template <std::size_t N>
+    constexpr span(std::array<value_type, N>& arr) noexcept : span(arr.data(), N)
+    {
+    }
+
+    template <typename Container>
+    constexpr span(const Container& container) : span(container.data(), container.size())
+    {
+    }
+
+    constexpr iterator begin() const noexcept { return ptr_; }
+    constexpr const_iterator cbegin() const noexcept { return begin(); }
+
+    constexpr iterator end() const noexcept { return begin() + size(); }
+    constexpr const_iterator cend() const noexcept { return end(); }
+
+    constexpr reference front() const { return *begin(); }
+    constexpr reference back() const { return *(--end()); }
+
+    constexpr reference operator[](size_type idx) const { return *(begin() + idx); }
+    constexpr pointer data() const noexcept { return ptr_; }
+
+    constexpr size_type size() const noexcept { return size_; }
+
+    private:
+    pointer ptr_;
+    size_type size_;
+};
+
+} // namespace ck