(svn r25889) -Codechange: Add forgotten file.

src/core/smallstack_type.hpp

@@ -0,0 +1,201 @@
+/* $Id$ */
+
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file smallstack_type.hpp Minimal stack that uses a pool to avoid pointers and doesn't allocate any heap memory if there is only one valid item. */
+
+#ifndef SMALLSTACK_TYPE_HPP
+#define SMALLSTACK_TYPE_HPP
+
+#include "pool_type.hpp"
+#include "pool_func.hpp"
+
+/**
+ * Base class for SmallStack. We cannot add this into SmallStack itself as
+ * certain compilers don't like it.
+ */
+template <typename Tindex, typename Titem>
+class SmallStackItem {
+protected:
+	Tindex next; ///< Pool index of next item.
+	Titem value; ///< Value of current item.
+
+	/**
+	 * Create a new item.
+	 * @param value Value of the item.
+	 * @param next Next item in the stack.
+	 */
+	inline SmallStackItem(const Titem &value, Tindex next) :
+		next(next), value(value) {}
+};
+
+/**
+ * Minimal stack that uses a pool to avoid pointers. It has some peculiar
+ * properties that make it useful for passing around lists of IDs but not much
+ * else:
+ * 1. It always includes an invalid item as bottom.
+ * 2. It doesn't have a deep copy operation but uses smart pointers instead.
+ *    Every copy is thus implicitly shared.
+ * 3. Its items are immutable.
+ * 4. Due to 2. and 3. memory management can be done by "branch counting".
+ *    Whenever you copy a smallstack, the first item on the heap increases its
+ *    branch_count, signifying that there are multiple items "in front" of it.
+ *    When deleting a stack items are deleted up to the point where
+ *    branch_count > 0.
+ * 5. You can choose your own index type, so that you can align it with your
+ *    value type. E.G. value types of 16 bits length like to be combined with
+ *    index types of the same length.
+ * @tparam Titem Value type to be used.
+ * @tparam Tindex Index type to use for the pool.
+ * @tparam Tinvalid Invalid item to keep at the bottom of each stack.
+ * @tparam Tgrowth_step Growth step for pool.
+ * @tparam Tmax_size Maximum size for pool.
+ */
+template <typename Titem, typename Tindex, Titem Tinvalid, size_t Tgrowth_step, size_t Tmax_size>
+class SmallStack : public SmallStackItem<Tindex, Titem> {
+protected:
+	class PooledSmallStack;
+
+	/**
+	 * Create a branch in the pool if necessary.
+	 */
+	void Branch()
+	{
+		if (PooledSmallStack::IsValidID(this->next)) {
+			PooledSmallStack::Get(this->next)->CreateBranch();
+		}
+	}
+
+public:
+	typedef SmallStackItem<Tindex, Titem> Item;
+	typedef Pool<PooledSmallStack, Tindex, Tgrowth_step, Tmax_size, PT_NORMAL, true, false> SmallStackPool;
+
+	/**
+	 * Constructor for a stack with one or two items in it.
+	 * @param value Initial item. If not missing or Tinvalid there will be Tinvalid below it.
+	 */
+	inline SmallStack(const Titem &value = Tinvalid) : Item(value, Tmax_size) {}
+
+	/**
+	 * Remove the head of stack and all other items members that are unique to it.
+	 */
+	inline ~SmallStack()
+	{
+		if (PooledSmallStack::IsValidID(this->next)) {
+			PooledSmallStack *item = PooledSmallStack::Get(this->next);
+			if (item->NumBranches() == 0) {
+				delete item;
+			} else {
+				item->DeleteBranch();
+			}
+		}
+	}
+
+	/**
+	 * Shallow copy the stack, marking the first item as branched.
+	 * @param other Stack to copy from
+	 */
+	inline SmallStack(const SmallStack &other) : Item(other) { this->Branch(); }
+
+	/**
+	 * Shallow copy the stack, marking the first item as branched.
+	 * @param other Stack to copy from
+	 * @return This smallstack.
+	 */
+	inline SmallStack &operator=(const SmallStack &other)
+	{
+		if (this == &other) return *this;
+		this->~SmallStack();
+		this->next = other.next;
+		this->value = other.value;
+		this->Branch();
+		return *this;
+	}
+
+	/**
+	 * Push a new item onto the stack.
+	 * @param item Item to be pushed.
+	 */
+	inline void Push(const Titem &item)
+	{
+		if (this->value != Tinvalid) {
+			assert(PooledSmallStack::CanAllocateItem());
+			PooledSmallStack *next = new PooledSmallStack(this->value, this->next);
+			this->next = next->index;
+		}
+		this->value = item;
+	}
+
+	/**
+	 * Pop an item from the stack.
+	 * @return Current top of stack.
+	 */
+	inline Titem Pop()
+	{
+		Titem ret = this->value;
+		if (!PooledSmallStack::IsValidID(this->next)) {
+			this->value = Tinvalid;
+		} else {
+			PooledSmallStack *next = PooledSmallStack::Get(this->next);
+			static_cast<Item &>(*this) = *next;
+			if (next->NumBranches() == 0) {
+				delete next;
+			} else {
+				next->DeleteBranch();
+				this->Branch();
+			}
+		}
+		return ret;
+	}
+
+	/**
+	 * Check if the stack is empty.
+	 * @return If the stack is empty.
+	 */
+	inline bool IsEmpty() const
+	{
+		return this->value == Tinvalid && !PooledSmallStack::IsValidID(this->next);
+	}
+
+	/**
+	 * Check if the given item is contained in the stack.
+	 * @param item Item to look for.
+	 * @return If the item is in the stack.
+	 */
+	inline bool Contains(const Titem &item) const
+	{
+		if (item == Tinvalid || item == this->value) return true;
+		const SmallStack *in_list = this;
+		while (PooledSmallStack::IsValidID(in_list->next)) {
+			in_list = static_cast<const SmallStack *>(
+					static_cast<const Item *>(PooledSmallStack::Get(in_list->next)));
+			if (in_list->value == item) return true;
+		}
+		return false;
+	}
+
+protected:
+	static SmallStackPool _pool;
+
+	/**
+	 * SmallStack item that can be kept in a pool (by having an index).
+	 */
+	class PooledSmallStack : public Item, public SmallStackPool::template PoolItem<&SmallStack::_pool> {
+	private:
+		Tindex branch_count; ///< Number of branches in the tree structure this item is parent of
+	public:
+		PooledSmallStack(Titem value, Tindex next) : Item(value, next), branch_count(0) {}
+
+		inline void CreateBranch() { ++this->branch_count; }
+		inline void DeleteBranch() { --this->branch_count; }
+		inline Tindex NumBranches() { return this->branch_count; }
+	};
+};
+
+
+#endif