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  Red Black Trees
  (C) 1999  Andrea Arcangeli <andrea@suse.de>
  This program 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; either version 2 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA


  To use rbtrees you'll have to implement your own insert and search cores.
  This will avoid us to use callbacks and to drop drammatically performances.
  I know it's not the cleaner way,  but in C (not in C++) to get
  performances and genericity...

  Some example of insert and search follows here. The search is a plain
  normal search over an ordered tree. The insert instead must be implemented
  int two steps: as first thing the code must insert the element in
  order as a red leaf in the tree, then the support library function
  rb_insert_color() must be called. Such function will do the
  not trivial work to rebalance the rbtree if necessary.

static inline struct page * rb_search_page_cache(struct inode * inode,
                                     unsigned long offset)
      struct rb_node * n = inode->i_rb_page_cache.rb_node;
      struct page * page;

      while (n)
            page = rb_entry(n, struct page, rb_page_cache);

            if (offset < page->offset)
                  n = n->rb_left;
            else if (offset > page->offset)
                  n = n->rb_right;
                  return page;
      return NULL;

static inline struct page * __rb_insert_page_cache(struct inode * inode,
                                       unsigned long offset,
                                       struct rb_node * node)
      struct rb_node ** p = &inode->i_rb_page_cache.rb_node;
      struct rb_node * parent = NULL;
      struct page * page;

      while (*p)
            parent = *p;
            page = rb_entry(parent, struct page, rb_page_cache);

            if (offset < page->offset)
                  p = &(*p)->rb_left;
            else if (offset > page->offset)
                  p = &(*p)->rb_right;
                  return page;

      rb_link_node(node, parent, p);

      return NULL;

static inline struct page * rb_insert_page_cache(struct inode * inode,
                                     unsigned long offset,
                                     struct rb_node * node)
      struct page * ret;
      if ((ret = __rb_insert_page_cache(inode, offset, node)))
            goto out;
      rb_insert_color(node, &inode->i_rb_page_cache);
      return ret;

#ifndef     _LINUX_RBTREE_H
#define     _LINUX_RBTREE_H

#include <stdlib.h>

struct rb_node
      unsigned long  rb_parent_color;
#define     RB_RED            0
#define     RB_BLACK    1
      struct rb_node *rb_right;
      struct rb_node *rb_left;
} __attribute__((aligned(sizeof(long))));
    /* The alignment might seem pointless, but allegedly CRIS needs it */

struct rb_root
      struct rb_node *rb_node;

#define rb_parent(r)   ((struct rb_node *)((r)->rb_parent_color & ~3))
#define rb_color(r)   ((r)->rb_parent_color & 1)
#define rb_is_red(r)   (!rb_color(r))
#define rb_is_black(r) rb_color(r)
#define rb_set_red(r)  do { (r)->rb_parent_color &= ~1; } while (0)
#define rb_set_black(r)  do { (r)->rb_parent_color |= 1; } while (0)

static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p)
      rb->rb_parent_color = (rb->rb_parent_color & 3) | (unsigned long)p;
static inline void rb_set_color(struct rb_node *rb, int color)
      rb->rb_parent_color = (rb->rb_parent_color & ~1) | color;

#define RB_ROOT   (struct rb_root) { NULL, }
#define     rb_entry(ptr, type, member) container_of(ptr, type, member)

#define RB_EMPTY_ROOT(root)   ((root)->rb_node == NULL)
#define RB_EMPTY_NODE(node)   (rb_parent(node) == node)
#define RB_CLEAR_NODE(node)   (rb_set_parent(node, node))

extern void rb_insert_color(struct rb_node *, struct rb_root *);
extern void rb_erase(struct rb_node *, struct rb_root *);

/* Find logical next and previous nodes in a tree */
extern struct rb_node *rb_first(struct rb_root *);

static inline void rb_link_node(struct rb_node * node, struct rb_node * parent,
                        struct rb_node ** rb_link)
      node->rb_parent_color = (unsigned long )parent;
      node->rb_left = node->rb_right = NULL;

      *rb_link = node;

#endif      /* _LINUX_RBTREE_H */

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