Mbed OS Reference | Span.h Source File

 /* mbed Microcontroller Library
  * Copyright (c) 2018-2019 ARM Limited
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 
 #ifndef MBED_PLATFORM_SPAN_H_
 #define MBED_PLATFORM_SPAN_H_
 
 #include <algorithm>
 #include <iterator>
 #include <stddef.h>
 #include <stdint.h>
 
 #include "platform/mbed_assert.h"
 
 namespace mbed {
 
 /** \addtogroup platform-public-api */
 /** @{*/
 
 /**
  * \defgroup platform_Span Span class
  * @{
  */
 
 // Internal details of Span
 // It is used construct Span from Span of convertible types (non const -> const)
 namespace span_detail {
 
 // If From type is convertible to To type, then the compilation constant value is
 // true; otherwise, it is false.
 template<typename From, typename To>
 class is_convertible {
     struct true_type {
         char x[512];
     };
     struct false_type { };
 
     static const From &generator();
     static true_type sink(const To &);
     static false_type sink(...);
 
 public:
     static const bool value = sizeof(true_type) == sizeof(sink(generator()));
 };
 
 }
 
 #if defined(DOXYGEN_ONLY)
 /**
  * Special value for the Extent parameter of Span.
  * If the type uses this value, then the size of the array is stored in the object
  * at runtime.
  *
  * @relates Span
  */
 const ptrdiff_t SPAN_DYNAMIC_EXTENT = -1;
 #else
 #define SPAN_DYNAMIC_EXTENT -1
 #endif
 
 /**
  * Nonowning view to a sequence of contiguous elements.
  *
  * Spans encapsulate a pointer to a sequence of contiguous elements and its size
  * into a single object. Span can replace the traditional pair of pointer and
  * size arguments passed as array definitions in function calls.
  *
  * @par Operations
  *
  * Span objects can be copied and assigned like regular value types with the help
  * of the copy constructor or the copy assignment (=) operator.
  *
  * You can retrieve elements of the object with the subscript ([]) operator. You can access the
  * pointer to the first element of the sequence viewed with data().
  * The function size() returns the number of elements in the sequence, and
  * empty() informs whether there is any element in the sequence.
  *
  * You can slice Span from the beginning of the sequence (first()), from the end
  * of the sequence (last()) or from an arbitrary point of the sequence (subspan()).
  *
  * @par Size encoding
  *
  * The size of the sequence can be encoded in the type itself or in the value of
  * the instance with the help of the template parameter Extent:
  *
  *   - Span<uint8_t, 6>: Span over a sequence of 6 elements.
  *   - Span<uint8_t>: Span over an arbitrary long sequence.
  *
  * When the size is encoded in the type itself, it is guaranteed that the Span
  * view is a valid sequence (not empty() and not NULL) - unless Extent equals 0.
  * The type system also prevents automatic conversion from Span of different
  * sizes. Finally, the Span object is internally represented as a single pointer.
  *
  * When the size of the sequence viewed is encoded in the Span value, Span
  * instances can view an empty sequence. The function empty() helps client code
  * decide whether Span is viewing valid content or not.
  *
  * @par Example
  *
  * - Encoding fixed size array: Array values in parameter decays automatically
  * to pointer, which leaves room for subtitle bugs:
  *
  * @code
     typedef uint8_t mac_address_t[6];
     void process_mac(mac_address_t);
 
     // compile just fine
     uint8_t *invalid_value = NULL;
     process_mac(invalid_value);
 
 
     // correct way
     typedef Span<uint8_t, 6> mac_address_t;
     void process_mac(mac_address_t);
 
     // compilation error
     uint8_t *invalid_value = NULL;
     process_mac(invalid_value);
 
     // compilation ok
     uint8_t valid_value[6];
     process_mac(valid_value);
  * @endcode
  *
  * - Arbitrary buffer: When dealing with multiple buffers, it becomes painful to
  * keep track of every buffer size and pointer.
  *
  * @code
     const uint8_t options_tag[OPTIONS_TAG_SIZE];
 
     struct parsed_value_t {
        uint8_t *header;
        uint8_t *options;
        uint8_t *payload;
        size_t payload_size;
     }
 
     parsed_value_t parse(uint8_t *buffer, size_t buffer_size)
     {
        parsed_value_t parsed_value { 0 };
 
        if (buffer != NULL && buffer_size <= MINIMAL_BUFFER_SIZE) {
            return parsed_value;
        }
 
        parsed_value.header = buffer;
        parsed_value.header_size = BUFFER_HEADER_SIZE;
 
        if (memcmp(buffer + HEADER_OPTIONS_INDEX, options_tag, sizeof(options_tag)) == 0) {
            options = buffer + BUFFER_HEADER_SIZE;
            payload = buffer + BUFFER_HEADER_SIZE + OPTIONS_SIZE;
            payload_size = buffer_size - BUFFER_HEADER_SIZE + OPTIONS_SIZE;
        } else {
            payload = buffer + BUFFER_HEADER_SIZE;
            payload_size = buffer_size - BUFFER_HEADER_SIZE;
        }
 
        return parsed_value;
     }
 
 
     //with Span
     struct parsed_value_t {
        Span<uint8_t> header;
        Span<uint8_t> options;
        Span<uint8_t> payload;
     }
 
     parsed_value_t parse(const Span<uint8_t> &buffer)
     {
        parsed_value_t parsed_value;
 
        if (buffer.size() <= MINIMAL_BUFFER_SIZE) {
            return parsed_value;
        }
 
        parsed_value.header = buffer.first(BUFFER_HEADER_SIZE);
 
        if (buffer.subspan<HEADER_OPTIONS_INDEX, sizeof(options_tag)>() == option_tag) {
            options = buffer.supspan(parsed_value.header.size(), OPTIONS_SIZE);
        }
 
        payload = buffer.subspan(parsed_value.header.size() + parsed_value.options.size());
 
        return parsed_value;
     }
  * @endcode
  *
  * @note You can create Span instances with the help of the function template
  * make_Span() and make_const_Span().
  *
  * @note Span<T, Extent> objects can be implicitly converted to Span<T> objects
  * where required.
  *
  * @tparam ElementType type of objects the Span views.
  *
  * @tparam Extent The size of the contiguous sequence viewed. The default value
  * SPAN_DYNAMIC_SIZE  is special because it allows construction of Span objects of
  * any size (set at runtime).
  */
 template<typename ElementType, ptrdiff_t Extent = SPAN_DYNAMIC_EXTENT>
 struct Span {
 
     /**
      * Type of the element contained
      */
     typedef ElementType element_type;
 
     /**
      * Type of the index.
      */
     typedef ptrdiff_t index_type;
 
     /**
      * Pointer to an ElementType
      */
     typedef element_type *pointer;
 
     /**
      * Reference to an ElementType
      */
     typedef element_type &reference;
 
     /**
      * Iterator to an ElementType
      */
     typedef pointer iterator;
 
     /**
      * Reverse iterator to an ElementType
      */
     typedef std::reverse_iterator<iterator> reverse_iterator;
 
     /**
      * Size of the Extent; -1 if dynamic.
      */
     static const index_type extent = Extent;
 
     MBED_STATIC_ASSERT(Extent >= 0, "Invalid extent for a Span");
 
     /**
      * Construct an empty Span.
      *
      * @post a call to size() returns 0, and data() returns NULL.
      *
      * @note This function is not accessible if Extent != SPAN_DYNAMIC_EXTENT or
      * Extent != 0 .
      */
     Span() :
         _data(NULL)
     {
         MBED_STATIC_ASSERT(
             Extent == 0,
             "Cannot default construct a static-extent Span (unless Extent is 0)"
         );
     }
 
     /**
      * Construct a Span from a pointer to a buffer and its size.
      *
      * @param ptr Pointer to the beginning of the data viewed.
      *
      * @param count Number of elements viewed.
      *
      * @pre [ptr, ptr + count) must be be a valid range.
      * @pre count must be equal to Extent.
      *
      * @post a call to size() returns Extent, and data() returns @p ptr.
      */
     Span(pointer ptr, index_type count) :
         _data(ptr)
     {
         MBED_ASSERT(count == Extent);
         MBED_ASSERT(Extent == 0 || ptr != NULL);
     }
 
     /**
      * Construct a Span from the range [first, last).
      *
      * @param first Pointer to the beginning of the data viewed.
      * @param last End of the range (element after the last element).
      *
      * @pre [first, last) must be be a valid range.
      * @pre first <= last.
      * @pre last - first must be equal to Extent.
      *
      * @post a call to size() returns Extent, and data() returns @p first.
      */
     Span(pointer first, pointer last) :
         _data(first)
     {
         MBED_ASSERT(first <= last);
         MBED_ASSERT((last - first) == Extent);
         MBED_ASSERT(Extent == 0 || first != NULL);
     }
 
     // AStyle ignore, not handling correctly below
     // *INDENT-OFF*
     /**
      * Construct a Span from the reference to an array.
      *
      * @param elements Reference to the array viewed.
      *
      * @post a call to size() returns Extent, and data() returns a
      * pointer to elements.
      */
     Span(element_type (&elements)[Extent]):
         _data(elements) { }
 
     /**
      * Construct a Span object from another Span of the same size.
      *
      * @param other The Span object used to construct this.
      *
      * @note For Span with a positive extent, this function is not accessible.
      *
      * @note OtherElementType(*)[] must be convertible to ElementType(*)[].
      */
     template<typename OtherElementType>
     Span(const Span<OtherElementType, Extent> &other):
         _data(other.data())
     {
         MBED_STATIC_ASSERT(
             (span_detail::is_convertible<OtherElementType (*)[1], ElementType (*)[1]>::value),
             "OtherElementType(*)[] should be convertible to ElementType (*)[]"
         );
     }
     // *INDENT-ON*
 
     /**
      * Return the size of the sequence viewed.
      *
      * @return The size of the sequence viewed.
      */
     index_type size() const
     {
         return Extent;
     }
 
     /**
      * Return if the sequence is empty or not.
      *
      * @return true if the sequence is empty and false otherwise.
      */
     bool empty() const
     {
         return size() == 0;
     }
 
     /**
      * Return an iterator to the first element of the sequence.
      *
      * @return An iterator to the first element of the sequence.
      */
     iterator begin() const
     {
         return _data;
     }
 
     /**
      * Return an iterator to the element following the last element of the sequence.
      *
      * @return An iterator to the element following the last element of the sequence.
      */
     iterator end() const
     {
         return _data + Extent;
     }
 
     /**
      * Return a reverse_iterator to the first element of the reversed sequence.
      *
      * @return A reverse_iterator to the first element of the reversed sequence.
      */
     reverse_iterator rbegin() const
     {
         return reverse_iterator(end());
     }
 
     /**
      * Return a reverse_iterator to the element following the last element of the reversed sequence.
      *
      * @return A reverse_iterator to the element following the last element of the reversed sequence.
      */
     reverse_iterator rend() const
     {
         return reverse_iterator(begin());
     }
 
     /**
      * Returns a reference to the element at position @p index.
      *
      * @param index Index of the element to access.
      *
      * @return A reference to the element at the index specified in input.
      *
      * @pre 0 <= index < Extent.
      */
     reference operator[](index_type index) const
     {
 #ifdef MBED_DEBUG
         MBED_ASSERT(0 <= index && index < Extent);
 #endif
         return _data[index];
     }
 
     /**
      * Return a pointer to the first element of the sequence or NULL if the Span
      * is empty().
      *
      * @return The pointer to the first element of the Span.
      */
     pointer data() const
     {
         return _data;
     }
 
     /**
      * Create a new Span over the first @p Count elements of the existing view.
      *
      * @tparam Count The number of element viewed by the new Span
      *
      * @return A new Span over the first @p Count elements.
      *
      * @pre Count >= 0 && Count <= size().
      */
     template<ptrdiff_t Count>
     Span<element_type, Count> first() const
     {
         MBED_STATIC_ASSERT(
             (0 <= Count) && (Count <= Extent),
             "Invalid subspan extent"
         );
         return Span<element_type, Count>(_data, Count);
     }
 
     /**
      * Create a new Span over the last @p Count elements of the existing view.
      *
      * @tparam Count The number of element viewed by the new Span.
      *
      * @return A new Span over the last @p Count elements.
      *
      * @pre Count >= 0 && Count <= size().
      */
     template<ptrdiff_t Count>
     Span<element_type, Count> last() const
     {
         MBED_STATIC_ASSERT(
             (0 <= Count) && (Count <= Extent),
             "Invalid subspan extent"
         );
         return Span<element_type, Count>(_data + (Extent - Count), Count);
     }
 
     // AStyle ignore, not handling correctly below
     // *INDENT-OFF*
     /**
      * Create a subspan that is a view of other Count elements; the view starts at
      * element Offset.
      *
      * @tparam Offset The offset of the first element viewed by the subspan.
      *
      * @tparam Count The number of elements present in the subspan. If Count
      * is equal to SPAN_DYNAMIC_EXTENT, then a Span starting at offset and
      * containing the rest of the elements is returned.
      *
      * @return A subspan of this starting at Offset and Count long.
      */
     template<std::ptrdiff_t Offset, std::ptrdiff_t Count>
     Span<element_type, Count == SPAN_DYNAMIC_EXTENT ? Extent - Offset : Count>
     subspan() const
     {
         MBED_STATIC_ASSERT(
             0 <= Offset && Offset <= Extent,
             "Invalid subspan offset"
         );
         MBED_STATIC_ASSERT(
             (Count == SPAN_DYNAMIC_EXTENT) ||
             (0 <= Count && (Count + Offset) <= Extent),
             "Invalid subspan count"
         );
         return Span<element_type, Count == SPAN_DYNAMIC_EXTENT ? Extent - Offset : Count>(
             _data + Offset,
             Count == SPAN_DYNAMIC_EXTENT ? Extent - Offset : Count
         );
     }
     // *INDENT-ON*
 
     /**
      * Create a new Span over the first @p count elements of the existing view.
      *
      * @param count The number of element viewed by the new Span.
      *
      * @return A new Span over the first @p count elements.
      */
     Span<element_type, SPAN_DYNAMIC_EXTENT> first(index_type count) const
     {
         MBED_ASSERT(0 <= count && count <= Extent);
         return Span<element_type, SPAN_DYNAMIC_EXTENT>(_data, count);
     }
 
     /**
      * Create a new Span over the last @p count elements of the existing view.
      *
      * @param count The number of elements viewed by the new Span.
      *
      * @return A new Span over the last @p count elements.
      */
     Span<element_type, SPAN_DYNAMIC_EXTENT> last(index_type count) const
     {
         MBED_ASSERT(0 <= count && count <= Extent);
         return Span<element_type, SPAN_DYNAMIC_EXTENT>(
                    _data + (Extent - count),
                    count
                );
     }
 
     /**
      * Create a subspan that is a view of other count elements; the view starts at
      * element offset.
      *
      * @param offset The offset of the first element viewed by the subspan.
      *
      * @param count The number of elements present in the subspan. If Count
      * is equal to SPAN_DYNAMIC_EXTENT, then a span starting at offset and
      * containing the rest of the elements is returned.
      *
      * @return
      */
     Span<element_type, SPAN_DYNAMIC_EXTENT> subspan(
         index_type offset, index_type count = SPAN_DYNAMIC_EXTENT
     ) const
     {
         MBED_ASSERT(0 <= offset && offset <= Extent);
         MBED_ASSERT(
             (count == SPAN_DYNAMIC_EXTENT) ||
             (0 <= count && (count + offset) <= Extent)
         );
         return Span<element_type, SPAN_DYNAMIC_EXTENT>(
                    _data + offset,
                    count == SPAN_DYNAMIC_EXTENT ? Extent - offset : count
                );
     }
 
 private:
     pointer _data;
 };
 
 /**
  * Span specialization that handle dynamic size.
  */
 template<typename ElementType>
 struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
     /**
      * Type of the element contained.
      */
     typedef ElementType element_type;
 
     /**
      * Type of the index.
      */
     typedef ptrdiff_t index_type;
 
     /**
      * Pointer to an ElementType.
      */
     typedef element_type *pointer;
 
     /**
      * Reference to an ElementType.
      */
     typedef element_type &reference;
 
     /**
      * Iterator to an ElementType
      */
     typedef pointer iterator;
 
     /**
      * Reverse iterator to an ElementType
      */
     typedef std::reverse_iterator<iterator> reverse_iterator;
 
     /**
      * Size of the Extent; -1 if dynamic.
      */
     static const index_type extent = SPAN_DYNAMIC_EXTENT;
 
     /**
      * Construct an empty Span.
      *
      * @post a call to size() returns 0, and data() returns NULL.
      *
      * @note This function is not accessible if Extent != SPAN_DYNAMIC_EXTENT or
      * Extent != 0 .
      */
     Span() :
         _data(NULL), _size(0) { }
 
     /**
      * Construct a Span from a pointer to a buffer and its size.
      *
      * @param ptr Pointer to the beginning of the data viewed.
      *
      * @param count Number of elements viewed.
      *
      * @pre [ptr, ptr + count) must be be a valid range.
      * @pre count must be equal to extent.
      *
      * @post a call to size() returns count, and data() returns @p ptr.
      */
     Span(pointer ptr, index_type count) :
         _data(ptr), _size(count)
     {
         MBED_ASSERT(count >= 0);
         MBED_ASSERT(ptr != NULL || count == 0);
     }
 
     /**
      * Construct a Span from the range [first, last).
      *
      * @param first Pointer to the beginning of the data viewed.
      * @param last End of the range (element after the last element).
      *
      * @pre [first, last) must be be a valid range.
      * @pre first <= last.
      *
      * @post a call to size() returns the result of (last - first), and
      * data() returns @p first.
      */
     Span(pointer first, pointer last) :
         _data(first), _size(last - first)
     {
         MBED_ASSERT(first <= last);
         MBED_ASSERT(first != NULL  || (last - first) == 0);
     }
 
     // AStyle ignore, not handling correctly below
     // *INDENT-OFF*
     /**
      * Construct a Span from the reference to an array.
      *
      * @param elements Reference to the array viewed.
      *
      * @tparam Count Number of elements of T presents in the array.
      *
      * @post a call to size() returns Count, and data() returns a
      * pointer to elements.
      */
     template<size_t Count>
     Span(element_type (&elements)[Count]):
         _data(elements), _size(Count) { }
 
     /**
      * Construct a Span object from another Span.
      *
      * @param other The Span object used to construct this.
      *
      * @note For Span with a positive extent, this function is not accessible.
      *
      * @note OtherElementType(*)[] must be convertible to ElementType(*)[].
      */
     template<typename OtherElementType, ptrdiff_t OtherExtent>
     Span(const Span<OtherElementType, OtherExtent> &other):
         _data(other.data()), _size(other.size())
     {
         MBED_STATIC_ASSERT(
             (span_detail::is_convertible<OtherElementType (*)[1], ElementType (*)[1]>::value),
             "OtherElementType(*)[] should be convertible to ElementType (*)[]"
         );
     }
     // *INDENT-ON*
 
     /**
      * Return the size of the array viewed.
      *
      * @return The number of elements present in the array viewed.
      */
     index_type size() const
     {
         return _size;
     }
 
     /**
      * Return if the sequence viewed is empty or not.
      *
      * @return true if the sequence is empty and false otherwise.
      */
     bool empty() const
     {
         return size() == 0;
     }
 
     /**
      * Return an iterator to the first element of the sequence.
      *
      * @return An iterator to the first element of the sequence.
      */
     iterator begin() const
     {
         return _data;
     }
 
     /**
      * Return an iterator to the element following the last element of the sequence.
      *
      * @return An iterator to the element following the last element of the sequence.
      */
     iterator end() const
     {
         return _data + _size;
     }
 
     /**
      * Return a reverse_iterator to the first element of the reversed sequence.
      *
      * @return A reverse_iterator to the first element of the reversed sequence.
      */
     reverse_iterator rbegin() const
     {
         return reverse_iterator(end());
     }
 
     /**
      * Return a reverse_iterator to the element following the last element of the reversed sequence.
      *
      * @return A reverse_iterator to the element following the last element of the reversed sequence.
      */
     reverse_iterator rend() const
     {
         return reverse_iterator(begin());
     }
 
     /**
      * Access to an element of the sequence.
      *
      * @param index Element index to access.
      *
      * @return A reference to the element at the index specified in input.
      *
      * @pre index is less than size().
      */
     reference operator[](index_type index) const
     {
 #ifdef MBED_DEBUG
         MBED_ASSERT(0 <= index && index < _size);
 #endif
         return _data[index];
     }
 
     /**
      * Get the raw pointer to the sequence viewed.
      *
      * @return The raw pointer to the first element viewed.
      */
     pointer data() const
     {
         return _data;
     }
 
     /**
      * Create a new Span over the first @p Count elements of the existing view.
      *
      * @tparam Count The number of elements viewed by the new Span.
      *
      * @return A new Span over the first @p Count elements.
      *
      * @pre Count >= 0 && Count <= size().
      */
     template<ptrdiff_t Count>
     Span<element_type, Count> first() const
     {
         MBED_ASSERT((Count >= 0) && (Count <= _size));
         return Span<element_type, Count>(_data, Count);
     }
 
     /**
      * Create a new Span over the last @p Count elements of the existing view.
      *
      * @tparam Count The number of elements viewed by the new Span.
      *
      * @return A new Span over the last @p Count elements.
      *
      * @pre Count >= 0 && Count <= size().
      */
     template<ptrdiff_t Count>
     Span<element_type, Count> last() const
     {
         MBED_ASSERT((0 <= Count) && (Count <= _size));
         return Span<element_type, Count>(_data + (_size - Count), Count);
     }
 
     /**
      * Create a subspan that is a view other Count elements; the view starts at
      * element Offset.
      *
      * @tparam Offset The offset of the first element viewed by the subspan.
      *
      * @tparam Count The number of elements present in the subspan. If Count
      * is equal to SPAN_DYNAMIC_EXTENT, then a Span starting at offset and
      * containing the rest of the elements is returned.
      *
      * @return A subspan of this starting at Offset and Count long.
      */
     template<std::ptrdiff_t Offset, std::ptrdiff_t Count>
     Span<element_type, Count>
     subspan() const
     {
         MBED_ASSERT(0 <= Offset && Offset <= _size);
         MBED_ASSERT(
             (Count == SPAN_DYNAMIC_EXTENT) ||
             (0 <= Count && (Count + Offset) <= _size)
         );
         return Span<element_type, Count>(
                    _data + Offset,
                    Count == SPAN_DYNAMIC_EXTENT ? _size - Offset : Count
                );
     }
 
     /**
      * Create a new Span over the first @p count elements of the existing view.
      *
      * @param count The number of elements viewed by the new Span.
      *
      * @return A new Span over the first @p count elements.
      */
     Span<element_type, SPAN_DYNAMIC_EXTENT> first(index_type count) const
     {
         MBED_ASSERT(0 <= count && count <= _size);
         return Span<element_type, SPAN_DYNAMIC_EXTENT>(_data, count);
     }
 
     /**
      * Create a new Span over the last @p count elements of the existing view.
      *
      * @param count The number of elements viewed by the new Span.
      *
      * @return A new Span over the last @p count elements.
      */
     Span<element_type, SPAN_DYNAMIC_EXTENT> last(index_type count) const
     {
         MBED_ASSERT(0 <= count && count <= _size);
         return Span<element_type, SPAN_DYNAMIC_EXTENT>(
                    _data + (_size - count),
                    count
                );
     }
 
     /**
      * Create a subspan that is a view of other count elements; the view starts at
      * element offset.
      *
      * @param offset The offset of the first element viewed by the subspan.
      *
      * @param count The number of elements present in the subspan. If Count
      * is equal to SPAN_DYNAMIC_EXTENT, then a Span starting at offset and
      * containing the rest of the elements is returned.
      *
      * @return A subspan of this starting at offset and count long.
      */
     Span<element_type, SPAN_DYNAMIC_EXTENT> subspan(
         index_type offset, index_type count = SPAN_DYNAMIC_EXTENT
     ) const
     {
         MBED_ASSERT(0 <= offset && offset <= _size);
         MBED_ASSERT(
             (count == SPAN_DYNAMIC_EXTENT) ||
             (0 <= count && (count + offset) <= _size)
         );
         return Span<element_type, SPAN_DYNAMIC_EXTENT>(
                    _data + offset,
                    count == SPAN_DYNAMIC_EXTENT ? _size - offset : count
                );
     }
 
 private:
     pointer _data;
     index_type _size;
 };
 
 /**
  * Equality operator between two Span objects.
  *
  * @param lhs Left side of the binary operation.
  * @param rhs Right side of the binary operation.
  *
  * @return True if Spans in input have the same size and the same content and
  * false otherwise.
  *
  * @relates Span
  */
 template<typename T, typename U, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
 bool operator==(const Span<T, LhsExtent> &lhs, const Span<U, RhsExtent> &rhs)
 {
     if (lhs.size() != rhs.size()) {
         return false;
     }
 
     if (lhs.data() == rhs.data()) {
         return true;
     }
 
     return std::equal(lhs.data(), lhs.data() + lhs.size(), rhs.data());
 }
 
 // AStyle ignore, not handling correctly below
 // *INDENT-OFF*
 /**
  * Equality operation between a Span and a reference to a C++ array.
  *
  * @param lhs Left side of the binary operation.
  * @param rhs Right side of the binary operation.
  *
  * @return True if elements in input have the same size and the same content and
  * false otherwise.
  */
 template<typename T, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
 bool operator==(const Span<T, LhsExtent> &lhs, T (&rhs)[RhsExtent])
 {
     return lhs == Span<T>(rhs);
 }
 
 /**
  * Equality operation between a Span and a reference to a C++ array.
  *
  * @param lhs Left side of the binary operation.
  * @param rhs Right side of the binary operation.
  *
  * @return True if elements in input have the same size and the same content
  * and false otherwise.
  */
 template<typename T, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
 bool operator==(T (&lhs)[LhsExtent], const Span<T, RhsExtent> &rhs)
 {
     return Span<T>(lhs) == rhs;
 }
 
 /**
  * Not equal operator
  *
  * @param lhs Left side of the binary operation.
  * @param rhs Right side of the binary operation.
  *
  * @return True if arrays in input do not have the same size or the same content
  * and false otherwise.
  *
  * @relates Span
  */
 template<typename T, typename U, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
 bool operator!=(const Span<T, LhsExtent> &lhs, const Span<U, RhsExtent> &rhs)
 {
     return !(lhs == rhs);
 }
 
 /**
  * Not Equal operation between a Span and a reference to a C++ array.
  *
  * @param lhs Left side of the binary operation.
  * @param rhs Right side of the binary operation.
  *
  * @return True if elements in input have the same size and the same content
  * and false otherwise.
  */
 template<typename T, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
 bool operator!=(const Span<T, LhsExtent> &lhs, T (&rhs)[RhsExtent])
 {
     return !(lhs == Span<T, RhsExtent>(rhs));
 }
 
 /**
  * Not Equal operation between a Span and a reference to a C++ array.
  *
  * @param lhs Left side of the binary operation.
  * @param rhs Right side of the binary operation.
  *
  * @return True if elements in input have the same size and the same content
  * and false otherwise.
  */
 template<typename T, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
 bool operator!=(T (&lhs)[LhsExtent], const Span<T, RhsExtent> &rhs)
 {
     return !(Span<T, LhsExtent>(lhs) == rhs);
 }
 
 /**
  * Generate a Span from a reference to a C/C++ array.
  *
  * @tparam T Type of elements held in elements.
  * @tparam Extent Number of items held in elements.
  *
  * @param elements The reference to the array viewed.
  *
  * @return The Span to elements.
  *
  * @note This helper avoids the typing of template parameter when Span is
  * created 'inline'.
  *
  * @relates Span
  */
 template<typename T, size_t Size>
 Span<T, Size> make_Span(T (&elements)[Size])
 {
     return Span<T, Size>(elements);
 }
 
 /**
  * Generate a Span from a pointer to a C/C++ array.
  *
  * @tparam Extent Number of items held in elements.
  * @tparam T Type of elements held in elements.
  *
  * @param elements The reference to the array viewed.
  *
  * @return The Span to elements.
  *
  * @note This helper avoids the typing of template parameter when Span is
  * created 'inline'.
  */
 template<ptrdiff_t Extent, typename T>
 Span<T, Extent> make_Span(T *elements)
 {
     return Span<T, Extent>(elements, Extent);
 }
 
 /**
  * Generate a Span from a C/C++ pointer and the size of the array.
  *
  * @tparam T Type of elements held in array_ptr.
  *
  * @param array_ptr The pointer to the array viewed.
  * @param array_size The number of T elements in the array.
  *
  * @return The Span to array_ptr with a size of array_size.
  *
  * @note This helper avoids the typing of template parameter when Span is
  * created 'inline'.
  * 
  * @relates Span
  */
 template<typename T>
 Span<T> make_Span(T *array_ptr, ptrdiff_t array_size)
 {
     return Span<T>(array_ptr, array_size);
 }
 
 /**
  * Generate a Span to a const content from a reference to a C/C++ array.
  *
  * @tparam T Type of elements held in elements.
  * @tparam Extent Number of items held in elements.
  *
  * @param elements The array viewed.
  * @return The Span to elements.
  *
  * @note This helper avoids the typing of template parameter when Span is
  * created 'inline'.
  */
 template<typename T, size_t Extent>
 Span<const T, Extent> make_const_Span(const T (&elements)[Extent])
 {
     return Span<const T, Extent>(elements);
 }
 // *INDENT-ON*
 /**
  * Generate a Span to a const content from a pointer to a C/C++ array.
  *
  * @tparam Extent Number of items held in elements.
  * @tparam T Type of elements held in elements.
  *
  * @param elements The reference to the array viewed.
  *
  * @return The Span to elements.
  *
  * @note This helper avoids the typing of template parameter when Span is
  * created 'inline'.
  *
  * @relates Span
  */
 template<size_t Extent, typename T>
 Span<const T, Extent> make_const_Span(const T *elements)
 {
     return Span<const T, Extent>(elements, Extent);
 }
 
 /**
  * Generate a Span to a const content from a C/C++ pointer and the size of the
  * array.
  *
  * @tparam T Type of elements held in array_ptr.
  *
  * @param array_ptr The pointer to the array to viewed.
  * @param array_size The number of T elements in the array.
  *
  * @return The Span to array_ptr with a size of array_size.
  *
  * @note This helper avoids the typing of template parameter when Span is
  * created 'inline'.
  *
  * @relates Span
  */
 template<typename T>
 Span<const T> make_const_Span(T *array_ptr, size_t array_size)
 {
     return Span<const T>(array_ptr, array_size);
 }
 
 /**@}*/
 
 /**@}*/
 
 } // namespace mbed
 
 #endif /* MBED_PLATFORM_SPAN_H_ */
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