bird/filter/tree.c

/*
 *	Filters: utility functions
 *
 *	Copyright 1998 Pavel Machek <pavel@ucw.cz>
 *
 *	Can be freely distributed and used under the terms of the GNU GPL.
 */

#include "lib/alloca.h"
#include "nest/bird.h"
#include "conf/conf.h"
#include "filter/filter.h"

/**
 * find_tree
 * @t: tree to search in
 * @val: value to find
 *
 * Search for given value in the tree. I relies on fact that sorted tree is populated
 * by &f_val structures (that can be compared by val_compare()). In each node of tree, 
 * either single value (then t->from==t->to) or range is present.
 *
 * Both set matching and |switch() { }| construction is implemented using this function,
 * thus both are as fast as they can be.
 */
struct f_tree *
find_tree(struct f_tree *t, struct f_val val)
{
  if (!t)
    return NULL;
  if ((val_compare(t->from, val) != 1) &&
      (val_compare(t->to, val) != -1))
    return t;
  if (val_compare(t->from, val) == -1)
    return find_tree(t->right, val);
  else
    return find_tree(t->left, val);
}

static struct f_tree *
build_tree_rec(struct f_tree **buf, int l, int h)
{
  struct f_tree *n;
  int pos;

  if (l >= h)
    return NULL;

  pos = (l+h)/2;
  n = buf[pos];
  n->left = build_tree_rec(buf, l, pos);
  n->right = build_tree_rec(buf, pos+1, h);
  return n;
}


/**
 * build_tree
 * @from: degenerated tree (linked by @tree->left) to be transformed into form suitable for find_tree()
 *
 * Transforms denerated tree into balanced tree.
 */
struct f_tree *
build_tree(struct f_tree *from)
{
  struct f_tree *tmp, *root;
  struct f_tree **buf;
  int len, i;

  if (from == NULL)
    return NULL;

  len = 0;
  for (tmp = from; tmp != NULL; tmp = tmp->left)
    len++;

  if (len <= 1024)
    buf = alloca(len * sizeof(struct f_tree *));
  else
    buf = malloc(len * sizeof(struct f_tree *));

  /* Convert a degenerated tree into an sorted array */
  i = 0;
  for (tmp = from; tmp != NULL; tmp = tmp->left)
    buf[i++] = tmp;

  qsort(buf, len, sizeof(struct f_tree *), tree_compare);

  root = build_tree_rec(buf, 0, len);

  if (len > 1024)
    free(buf);

  return root;
}

struct f_tree *
f_new_tree(void)
{
  struct f_tree * ret;
  ret = cfg_alloc(sizeof(struct f_tree));
  ret->left = ret->right = NULL;
  ret->from.type = ret->to.type = T_VOID;
  ret->from.val.i = ret->to.val.i = 0;
  ret->data = NULL;
  return ret;
}

/**
 * same_tree
 * @t1: first tree to be compared
 * @t2: second one
 *
 * Compares two trees and returns 1 if they are same
 */
int
same_tree(struct f_tree *t1, struct f_tree *t2)
{
  if ((!!t1) != (!!t2))
    return 0;
  if (!t1)
    return 1;
  if (val_compare(t1->from, t2->from))
    return 0;
  if (val_compare(t1->to, t2->to))
    return 0;
  if (!same_tree(t1->left, t2->left))
    return 0;
  if (!same_tree(t1->right, t2->right))
    return 0;
  if (!i_same(t1->data, t2->data))
    return 0;
  return 1;
}