IntrusiveDList: Add list operations.

Author: SolidWallOfCode

code/include/swoc/IntrusiveDList.h

@@ -294,6 +294,101 @@ template <typename L> class IntrusiveDList {
   /// @return @a limit
   iterator erase(const iterator &start, const iterator &limit);
 
+  /** The nth element of the list.
+   *
+   * @param n Index of target element.
+   * @return An iterator to the element, an empty iterator if @a n is too large.
+   *
+   * @note This is linear in @a n, use with caution.
+   */
+  iterator nth(unsigned n);
+
+  /** Remove and return an initial subsequence.
+   *
+   * @param n Number of elements.
+   * @return The list of elements.
+   *
+   * If @a n is more than the length of the list, the entire list is returned.
+   */
+  self_type take_prefix(unsigned n);
+
+  /** Remove and return an initial subsequence.
+   *
+   * @param n Number of elements.
+   * @return The list of elements.
+   *
+   * If @a n is more than the length of the list @a this is unchanged and an empty list returned.
+   */
+  self_type split_prefix(unsigned n);
+
+  /** Remove and return a trailing subsequence.
+   *
+   * @param n Number of elements.
+   * @return The list of elements.
+   *
+   * If @a n is more than the length of the list, the entire list is returned.
+   */
+  self_type take_suffix(unsigned n);
+
+  /** Remove and return a trailing subsequence.
+   *
+   * @param n Number of elements.
+   * @return The list of elements.
+   *
+   * If @a n is more than the length of the list, @a this is unchanged and an empty list returned.
+   */
+  self_type split_suffix(unsigned n);
+
+  /** Append a list.
+   *
+   * @param src List to append.
+   * @return @a this
+   *
+   * The elements are removed from @a src, which becomes empty.
+   */
+  self_type & append(self_type & src);
+
+  /** Prepend a list.
+   *
+   * @param src List to prepend.
+   * @return @a this
+   *
+   * The elements are removed from @a src, which becomes empty.
+   */
+  self_type & prepend(self_type & src);
+
+  /** Splice in a list after an existing element.
+   *
+   * @param target Element in the lsit.
+   * @param src List to splice.
+   * @return @a this
+   */
+  self_type &insert_after(value_type *target, self_type & src);
+
+  /** Splice in a list before an existing element.
+   *
+   * @param target Element in the lsit.
+   * @param src List to splice.
+   * @return @a this
+   */
+  self_type &insert_before(value_type *target, self_type & src);
+
+  /** Splice in a list after an existing element.
+   *
+   * @param target Element in the lsit.
+   * @param src List to splice.
+   * @return @a this
+   */
+  self_type &insert_after(iterator const &target, self_type & src);
+
+  /** Splice in a list before an existing element.
+   *
+   * @param target Element in the lsit.
+   * @param src List to splice.
+   * @return @a this
+   */
+  self_type &insert_before(iterator const &target, self_type & src);
+
   /// Remove all elements.
   /// @note @b No memory management is done!
   /// @return This container.
@@ -744,6 +839,58 @@ IntrusiveDList<L>::insert_before(iterator const &target, value_type *v) -> self_
   return this->insert_before(target._v, v);
 }
 
+template <typename L>
+auto
+IntrusiveDList<L>::insert_after(value_type *target, self_type & src) -> self_type & {
+  if (target && src._count > 0) {
+    if (_tail == target) {
+      this->append(src);
+    } else { // invariant - @a target is not tail therefore has a successor.
+      L::next_ptr(src._tail) = L::next_ptr(target); // link @a src tail to @a target successor
+      L::prev_ptr(L::next_ptr(src._tail)) = src._tail;
+
+      L::prev_ptr(src._head) = target; // link @a src head to @target
+      L::next_ptr(target) = src._head;
+
+      _count += src._count;
+      src.clear();
+    }
+  }
+  return *this;
+}
+
+template <typename L>
+auto
+IntrusiveDList<L>::insert_after(iterator const &target, self_type & src) -> self_type & {
+  return this->insert_after(target._v, src);
+}
+
+template <typename L>
+auto
+IntrusiveDList<L>::insert_before(value_type *target, self_type & src) -> self_type & {
+  if (target && src._count > 0) {
+    if (_head == target) {
+      this->prepend(src);
+    } else { // invariant - @a target is not head and therefore has a predecessor.
+      L::prev_ptr(src._head) = L::prev_ptr(target); // link @a src head to @a target predecessor
+      L::next_ptr(L::prev_ptr(target)) = src._head;
+
+      L::next_ptr(src._tail) = target; // link @a src tail to @a target
+      L::prev_ptr(target) = src._tail;
+
+      _count += src._count;
+      src.clear();
+    }
+  }
+  return *this;
+}
+
+template <typename L>
+auto
+IntrusiveDList<L>::insert_before(iterator const &target, self_type & src) -> self_type & {
+  return this->insert_before(target._v, src);
+}
+
 template <typename L>
 auto
 IntrusiveDList<L>::erase(value_type *v) -> value_type * {
@@ -887,11 +1034,140 @@ IntrusiveDList<L>::clear() -> self_type & {
   return *this;
 }
 
+template <typename L>
+auto
+IntrusiveDList<L>::nth(unsigned int n) -> iterator {
+  if (n >= _count) {
+    return {};
+  }
+
+  value_type * spot;
+  if (n < _count/2) { // closer to head, count from there..
+    spot = _head;
+    while (n-- > 0) { spot = L::next_ptr(spot); }
+  } else { // count from tail
+    spot = _tail;
+    unsigned idx = _count - 1;
+    while (idx-- > n) { spot = L::prev_ptr(spot); }
+  }
+  return iterator_for(spot);
+}
+
+template <typename L>
+auto
+IntrusiveDList<L>::take_prefix(unsigned int n) -> self_type {
+
+  if (n == 0) {
+    return {};
+  }
+
+  if (_count <= n) {
+    return std::move(*this);
+  }
+
+  // Invariant - there is at least one element that will not be taken.
+
+  self_type zret;
+  value_type * spot = this->nth(n); // new @a head for @a this
+
+  zret._count = n;
+  zret._head = _head;
+  zret._tail = L::prev_ptr(spot);
+  L::next_ptr(zret._tail) = nullptr;
+
+  _count -= n;
+  _head = spot;
+  L::prev_ptr(_head) = nullptr;
+
+  return zret;
+}
+
+template <typename L>
+auto
+IntrusiveDList<L>::split_prefix(unsigned int n) -> self_type {
+  if (n <= _count) {
+    return this->take_prefix(n);
+  }
+  return {};
+}
+
+template <typename L>
+auto
+IntrusiveDList<L>::take_suffix(unsigned int n) -> self_type {
+
+  if (n == 0) {
+    return {};
+  }
+
+  if (_count <= n) {
+    return std::move(*this);
+  }
+
+  // Invariant - there is at least one element that will not be taken.
+
+  self_type zret;
+  value_type * spot = this->nth(_count - n - 1); // new @a tail for @a this
+
+  zret._count = n;
+  zret._head = L::next_ptr(spot);
+  L::prev_ptr(zret._head) = nullptr;
+  zret._tail = _tail;
+
+  _count -= n;
+  _tail = spot;
+  L::next_ptr(_tail) = nullptr;
+
+  return zret;
+}
+
+template <typename L>
+auto
+IntrusiveDList<L>::split_suffix(unsigned int n) -> self_type {
+  if (n <= _count) {
+    return this->take_suffix(n);
+  }
+  return {};
+}
+
+template <typename L>
+auto
+IntrusiveDList<L>::prepend(IntrusiveDList::self_type &src) -> self_type & {
+  if (src._count > 0) {
+    if (_count == 0) {
+      *this = std::move(src);
+    } else {
+      L::prev_ptr(_head)     = src._tail;
+      L::next_ptr(src._tail) = _head;
+      _count += src._count;
+      _head = src._head;
+      src.clear();
+    }
+  }
+  return *this;
+}
+
+template <typename L>
+auto
+IntrusiveDList<L>::append(IntrusiveDList::self_type &src) -> self_type & {
+  if (src._count > 0) {
+    if (_count == 0) {
+      *this = std::move(src);
+    } else {
+      L::next_ptr(_tail)     = src._head;
+      L::prev_ptr(src._head) = _tail;
+      _count += src._count;
+      _tail = src._tail;
+      src.clear();
+    }
+  }
+  return *this;
+}
+
 namespace detail {
 /// @cond INTERNAL_DETAIL
 // Make @c apply more convenient by allowing the function to take a reference type or pointer type
 // to the container elements. The pointer type is the base, plus a shim to convert from a reference
-// type functor to a pointer pointer type. The complex return type definition forces only one, but
+// type functor to a pointer type. The complex return type definition forces only one, but
 // not both, to be valid for a particular functor. This also must be done via free functions and not
 // method overloads because the compiler forces a match up of method definitions and declarations
 // before any template instantiation.

example/CMakeLists.txt

@@ -30,7 +30,7 @@ if (CMAKE_COMPILER_IS_GNUCXX)
     target_compile_options(ex_flat_space PRIVATE -Wall -Wextra -Werror)
 endif()
 
-add_executable(ex_diskstats ex_diskstats.cc)
+add_executable(ex_diskstats ex_diskstats.cc ../image/include/swoc/IntrusiveDList.h)
 target_link_libraries(ex_diskstats PUBLIC libswoc-static)
 if (CMAKE_COMPILER_IS_GNUCXX)
     target_compile_options(ex_diskstats PRIVATE -Wall -Wextra -Werror)