list.h

/*
 * Copyright © 2008, 2010 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

/**
 * \file list.h
 * \brief Doubly-linked list abstract container type.
 *
 * Each doubly-linked list has a sentinal head and tail node.  These nodes
 * contain no data.  The head sentinal can be identified by its \c prev
 * pointer being \c NULL.  The tail sentinal can be identified by its
 * \c next pointer being \c NULL.
 *
 * A list is empty if either the head sentinal's \c next pointer points to the
 * tail sentinal or the tail sentinal's \c prev poiner points to the head
 * sentinal.
 *
 * Instead of tracking two separate \c node structures and a \c list structure
 * that points to them, the sentinal nodes are in a single structure.  Noting
 * that each sentinal node always has one \c NULL pointer, the \c NULL
 * pointers occupy the same memory location.  In the \c list structure
 * contains a the following:
 *
 *   - A \c head pointer that represents the \c next pointer of the
 *     head sentinal node.
 *   - A \c tail pointer that represents the \c prev pointer of the head
 *     sentinal node and the \c next pointer of the tail sentinal node.  This
 *     pointer is \b always \c NULL.
 *   - A \c tail_prev pointer that represents the \c prev pointer of the
 *     tail sentinal node.
 *
 * Therefore, if \c head->next is \c NULL or \c tail_prev->prev is \c NULL,
 * the list is empty.
 *
 * To anyone familiar with "exec lists" on the Amiga, this structure should
 * be immediately recognizable.  See the following link for the original Amiga
 * operating system documentation on the subject.
 *
 * http://www.natami.net/dev/Libraries_Manual_guide/node02D7.html
 *
 * \author Ian Romanick <ian.d.romanick@intel.com>
 */

#pragma once
#ifndef LIST_CONTAINER_H
#define LIST_CONTAINER_H

#include <assert.h>

struct exec_node {
   struct exec_node *next;
   struct exec_node *prev;

#ifdef __cplusplus
   exec_node() : next(NULL), prev(NULL)
   {
      /* empty */
   }

   const exec_node *get_next() const
   {
      return next;
   }

   exec_node *get_next()
   {
      return next;
   }

   const exec_node *get_prev() const
   {
      return prev;
   }

   exec_node *get_prev()
   {
      return prev;
   }

   void remove()
   {
      next->prev = prev;
      prev->next = next;
      next = NULL;
      prev = NULL;
   }

   /**
    * Link a node with itself
    *
    * This creates a sort of degenerate list that is occasionally useful.
    */
   void self_link()
   {
      next = this;
      prev = this;
   }

   /**
    * Insert a node in the list after the current node
    */
   void insert_after(exec_node *after)
   {
      after->next = this->next;
      after->prev = this;

      this->next->prev = after;
      this->next = after;
   }
#endif
};

#ifdef __cplusplus
struct exec_node;

class iterator {
public:
   void next()
   {
   }

   void *get()
   {
      return NULL;
   }

   bool has_next() const
   {
      return false;
   }
};

class exec_list_iterator : public iterator {
public:
   exec_list_iterator(exec_node *n) : node(n), _next(n->next)
   {
      /* empty */
   }

   void next()
   {
      node = _next;
      _next = node->next;
   }

   void remove()
   {
      node->remove();
   }

   exec_node *get()
   {
      return node;
   }

   bool has_next() const
   {
      return _next != NULL;
   }

private:
   exec_node *node;
   exec_node *_next;
};

#define foreach_iter(iter_type, iter, container) \
   for (iter_type iter = container . iterator(); iter.has_next(); iter.next())
#endif


struct exec_list {
   struct exec_node *head;
   struct exec_node *tail;
   struct exec_node *tail_pred;

#ifdef __cplusplus
   exec_list()
   {
      make_empty();
   }

   void make_empty()
   {
      head = (exec_node *) & tail;
      tail = NULL;
      tail_pred = (exec_node *) & head;
   }

   bool is_empty() const
   {
      /* There are three ways to test whether a list is empty or not.
       *
       * - Check to see if the \c head points to the \c tail.
       * - Check to see if the \c tail_pred points to the \c head.
       * - Check to see if the \c head is the sentinal node by test whether its
       *   \c next pointer is \c NULL.
       *
       * The first two methods tend to generate better code on modern systems
       * because they save a pointer dereference.
       */
      return head == (exec_node *) &tail;
   }

   const exec_node *get_head() const
   {
      return !is_empty() ? head : NULL;
   }

   exec_node *get_head()
   {
      return !is_empty() ? head : NULL;
   }

   const exec_node *get_tail() const
   {
      return !is_empty() ? tail_pred : NULL;
   }

   exec_node *get_tail()
   {
      return !is_empty() ? tail_pred : NULL;
   }

   void push_head(exec_node *n)
   {
      n->next = head;
      n->prev = (exec_node *) &head;

      n->next->prev = n;
      head = n;
   }

   void push_tail(exec_node *n)
   {
      n->next = (exec_node *) &tail;
      n->prev = tail_pred;

      n->prev->next = n;
      tail_pred = n;
   }

   void push_degenerate_list_at_head(exec_node *n)
   {
      assert(n->prev->next == n);

      n->prev->next = head;
      head->prev = n->prev;
      n->prev = (exec_node *) &head;
      head = n;
   }

   /**
    * Move all of the nodes from this list to the target list
    */
   void move_nodes_to(exec_list *target)
   {
      target->head = head;
      target->tail = NULL;
      target->tail_pred = tail_pred;

      target->head->prev = (exec_node *) &target->head;
      target->tail_pred->next = (exec_node *) &target->tail;

      make_empty();
   }

   exec_list_iterator iterator()
   {
      return exec_list_iterator(head);
   }

   exec_list_iterator iterator() const
   {
      return exec_list_iterator((exec_node *) head);
   }
#endif
};

#endif /* LIST_CONTAINER_H */