radix-tree.c   [plain text]

/*
 * Modified to work in GCC in 2003 by Daniel Berlin 
 * Copyright (C) 2001 Momchil Velikov
 * Portions Copyright (C) 2001 Christoph Hellwig
 *
 * 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, 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
 * 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 this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include  "radix-tree.h"
#define ARRAY_SIZE(a) (sizeof (a) / sizeof ((a)[0]))
/*
 * Radix tree node definition.
 */
#define RADIX_TREE_MAP_SHIFT  6
#define RADIX_TREE_MAP_SIZE  (1UL << RADIX_TREE_MAP_SHIFT)
#define RADIX_TREE_MAP_MASK  (RADIX_TREE_MAP_SIZE-1)

struct radix_tree_node {
  unsigned int	count;
  void		*slots[RADIX_TREE_MAP_SIZE];
};

struct radix_tree_path {
  struct radix_tree_node *node, **slot;
};

#define RADIX_TREE_INDEX_BITS  (8 /* CHAR_BIT */ * sizeof(unsigned long))
#define RADIX_TREE_MAX_PATH (RADIX_TREE_INDEX_BITS/RADIX_TREE_MAP_SHIFT + 2)

static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH];


/*
 * This assumes that the caller has performed appropriate preallocation, and
 * that the caller has pinned this thread of control to the current CPU.
 */
static struct radix_tree_node *
radix_tree_node_alloc(struct radix_tree_root *root)
{
  struct radix_tree_node *ret;
  
  ret = (struct radix_tree_node *)
    calloc (1, sizeof (struct radix_tree_node));
  if (!ret)
    abort ();
  return ret;
}

static inline void
radix_tree_node_free(struct radix_tree_node *node)
{
  free (node);
}


/*
 *	Return the maximum key which can be store into a
 *	radix tree with height HEIGHT.
 */
static inline unsigned long radix_tree_maxindex(unsigned int height)
{
  return height_to_maxindex[height];
}

/*
 *	Extend a radix tree so it can store key @index.
 */
static int radix_tree_extend(struct radix_tree_root *root, unsigned long index)
{
  struct radix_tree_node *node;
  unsigned int height;
  
  /* Figure out what the height should be.  */
  height = root->height + 1;
  while (index > radix_tree_maxindex(height))
    height++;
  
  if (root->rnode) {
    do {
      if (!(node = radix_tree_node_alloc(root)))
	return -ENOMEM;
      
      /* Increase the height.  */
      node->slots[0] = root->rnode;
      node->count = 1;
      root->rnode = node;
      root->height++;
    } while (height > root->height);
  } else 
    root->height = height;
  
  return 0;
}

/**
 *	radix_tree_insert    -    insert into a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *	@item:		item to insert
 *
 *	Insert an item into the radix tree at position @index.
 */
int radix_tree_insert(struct radix_tree_root *root, unsigned long index,
		      void *item)
{
  struct radix_tree_node *node = NULL, *tmp, **slot;
  unsigned int height, shift;
  int error;
  
  /* Make sure the tree is high enough.  */
  if (index > radix_tree_maxindex(root->height)) {
    error = radix_tree_extend(root, index);
    if (error)
      return error;
  }
  
  slot = &root->rnode;
  height = root->height;
  shift = (height-1) * RADIX_TREE_MAP_SHIFT;
  
  while (height > 0) {
    if (*slot == NULL) {
      /* Have to add a child node.  */
      if (!(tmp = radix_tree_node_alloc(root)))
	return -ENOMEM;
      *slot = tmp;
      if (node)
	node->count++;
    }
    
    /* Go a level down.  */
    node = *slot;
    slot = (struct radix_tree_node **)
      (node->slots + ((index >> shift) & RADIX_TREE_MAP_MASK));
    shift -= RADIX_TREE_MAP_SHIFT;
    height--;
  }
  
  if (*slot != NULL)
    return -EEXIST;
  if (node)
    node->count++;
  
  *slot = item;
  return 0;
}

/**
 *	radix_tree_lookup    -    perform lookup operation on a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *
 *	Lookup them item at the position @index in the radix tree @root.
 */
void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
{
  unsigned int height, shift;
  struct radix_tree_node **slot;
  
  height = root->height;
  if (index > radix_tree_maxindex(height))
    return NULL;
  
  shift = (height-1) * RADIX_TREE_MAP_SHIFT;
  slot = &root->rnode;
  
  while (height > 0) {
    if (*slot == NULL)
      return NULL;
    
    slot = (struct radix_tree_node **)
      ((*slot)->slots + ((index >> shift) & RADIX_TREE_MAP_MASK));
    shift -= RADIX_TREE_MAP_SHIFT;
    height--;
  }
  
  return (void *) *slot;
}

static /* inline */ unsigned int
__lookup(struct radix_tree_root *root, void **results, unsigned long index,
	 unsigned int max_items, unsigned long *next_index)
{
  unsigned int nr_found = 0;
  unsigned int shift;
  unsigned int height = root->height;
  struct radix_tree_node *slot;
  
  shift = (height-1) * RADIX_TREE_MAP_SHIFT;
  slot = root->rnode;
  
  while (height > 0) {
    unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK;
    
    for ( ; i < RADIX_TREE_MAP_SIZE; i++) {
      if (slot->slots[i] != NULL)
	break;
      index &= ~((1 << shift) - 1);
      index += 1 << shift;
      if (index == 0)
	goto out;	/* 32-bit wraparound */
    }
    if (i == RADIX_TREE_MAP_SIZE)
      goto out;
    height--;
    if (height == 0) {	/* Bottom level: grab some items */
      unsigned long j = index & RADIX_TREE_MAP_MASK;
      
      for ( ; j < RADIX_TREE_MAP_SIZE; j++) {
	index++;
	if (slot->slots[j]) {
	  results[nr_found++] = slot->slots[j];
	  if (nr_found == max_items)
	    goto out;
	}
      }
    }
    shift -= RADIX_TREE_MAP_SHIFT;
    slot = slot->slots[i];
  }
 out:
  *next_index = index;
  return nr_found;
}

/**
 *	radix_tree_gang_lookup - perform multiple lookup on a radix tree
 *	@root:		radix tree root
 *	@results:	where the results of the lookup are placed
 *	@first_index:	start the lookup from this key
 *	@max_items:	place up to this many items at *results
 *
 *	Performs an index-ascending scan of the tree for present items.  Places
 *	them at *@results and returns the number of items which were placed at
 *	*@results.
 *
 *	The implementation is naive.
 */
unsigned int
radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
		       unsigned long first_index, unsigned int max_items)
{
  const unsigned long max_index = radix_tree_maxindex(root->height);
  unsigned long cur_index = first_index;
  unsigned int ret = 0;
  
  if (root->rnode == NULL)
    goto out;
  if (max_index == 0) {			/* Bah.  Special case */
    if (first_index == 0) {
      if (max_items > 0) {
	*results = root->rnode;
	ret = 1;
      }
    }
    goto out;
  }
  while (ret < max_items) {
    unsigned int nr_found;
    unsigned long next_index;	/* Index of next search */
    
    if (cur_index > max_index)
      break;
    nr_found = __lookup(root, results + ret, cur_index,
			max_items - ret, &next_index);
    ret += nr_found;
    if (next_index == 0)
      break;
    cur_index = next_index;
  }
 out:
  return ret;
}

/**
 *	radix_tree_delete    -    delete an item from a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *
 *	Remove the item at @index from the radix tree rooted at @root.
 *
 *	Returns the address of the deleted item, or NULL if it was not present.
 */
void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
{
  struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
  unsigned int height, shift;
  void *ret = NULL;
  
  height = root->height;
  if (index > radix_tree_maxindex(height))
    goto out;
  
  shift = (height-1) * RADIX_TREE_MAP_SHIFT;
  pathp->node = NULL;
  pathp->slot = &root->rnode;
  
  while (height > 0) {
    if (*pathp->slot == NULL)
      goto out;
    
    pathp[1].node = *pathp[0].slot;
    pathp[1].slot = (struct radix_tree_node **)
      (pathp[1].node->slots + ((index >> shift) & RADIX_TREE_MAP_MASK));
    pathp++;
    shift -= RADIX_TREE_MAP_SHIFT;
    height--;
  }
  
  ret = *pathp[0].slot;
  if (ret == NULL)
    goto out;
  
  *pathp[0].slot = NULL;
  while (pathp[0].node && --pathp[0].node->count == 0) {
    pathp--;
    *pathp[0].slot = NULL;
    radix_tree_node_free(pathp[1].node);
  }
  
  if (root->rnode == NULL)
    root->height = 0;  /* Empty tree, we can reset the height */
 out:
  return ret;
}


static unsigned long __maxindex(unsigned int height)
{
  unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
  unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
  
  if (tmp >= RADIX_TREE_INDEX_BITS)
    index = ~0UL;
  return index;
}

static void radix_tree_init_maxindex(void)
{
  unsigned int i;
  
  for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
    height_to_maxindex[i] = __maxindex(i);
}

void radix_tree_init(void)
{
  radix_tree_init_maxindex();
}