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/* Balanced binary trees using treaps.

   Copyright (C) 2000, 2002, 2003 Free Software Foundation, Inc.

   Contributed by Andy Vaught

This file is part of GCC.

GCC 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.

GCC 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 GCC; see the file COPYING.  If not, write to the Free

Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301, USA.  */

/* The idea is to balance the tree using pseudorandom numbers.  The

   main constraint on this implementation is that we have several

   distinct structures that have to be arranged in a binary tree.

   These structures all contain a BBT_HEADER() in front that gives the

   treap-related information.  The key and value are assumed to reside

   in the rest of the structure.

   When calling, we are also passed a comparison function that

   compares two nodes.  We don't implement a separate 'find' function

   here, but rather use separate functions for each variety of tree.

   We are also restricted to not copy treap structures, which most

   implementations find convenient, because we otherwise would need to

   know how long the structure is.

   This implementation is based on Stefan Nilsson's article in the

   July 1997 Doctor Dobb's Journal, "Treaps in Java".  */

#include "config.h"

#include "gfortran.h"

typedef struct gfc_treap

{

  BBT_HEADER (gfc_treap);

}

gfc_bbt;

/* Simple linear congruential pseudorandom number generator.  The

   period of this generator is 44071, which is plenty for our

   purposes.  */

static int

pseudo_random (void)

{

  static int x0 = 5341;

  x0 = (22611 * x0 + 10) % 44071;

  return x0;

}

/* Rotate the treap left.  */

static gfc_bbt *

rotate_left (gfc_bbt * t)

{

  gfc_bbt *temp;

  temp = t->right;

  t->right = t->right->left;

  temp->left = t;

  return temp;

}

/* Rotate the treap right.  */

static gfc_bbt *

rotate_right (gfc_bbt * t)

{

  gfc_bbt *temp;

  temp = t->left;

  t->left = t->left->right;

  temp->right = t;

  return temp;

}

/* Recursive insertion function.  Returns the updated treap, or

   aborts if we find a duplicate key.  */

static gfc_bbt *

insert (gfc_bbt * new, gfc_bbt * t, compare_fn compare)

{

  int c;

  if (t == NULL)

    return new;

  c = (*compare) (new, t);

  if (c < 0)

    {

      t->left = insert (new, t->left, compare);

      if (t->priority < t->left->priority)

        t = rotate_right (t);

    }

  else if (c > 0)

    {

      t->right = insert (new, t->right, compare);

      if (t->priority < t->right->priority)

        t = rotate_left (t);

    }

  else /* if (c == 0)  */

    gfc_internal_error("insert_bbt(): Duplicate key found!");

  return t;

}

/* Given root pointer, a new node and a comparison function, insert

   the new node into the treap.  It is an error to insert a key that

   already exists.  */

void

gfc_insert_bbt (void *root, void *new, compare_fn compare)

{

  gfc_bbt **r, *n;

  r = (gfc_bbt **) root;

  n = (gfc_bbt *) new;

  n->priority = pseudo_random ();

  *r = insert (n, *r, compare);

}

static gfc_bbt *

delete_root (gfc_bbt * t)

{

  gfc_bbt *temp;

  if (t->left == NULL)

    return t->right;

  if (t->right == NULL)

    return t->left;

  if (t->left->priority > t->right->priority)

    {

      temp = rotate_right (t);

      temp->right = delete_root (t);

    }

  else

    {

      temp = rotate_left (t);

      temp->left = delete_root (t);

    }

  return temp;

}

/* Delete an element from a tree.  The 'old' value does not

   necessarily have to point to the element to be deleted, it must

   just point to a treap structure with the key to be deleted.

   Returns the new root node of the tree.  */

static gfc_bbt *

delete_treap (gfc_bbt * old, gfc_bbt * t, compare_fn compare)

{

  int c;

  if (t == NULL)

    return NULL;

  c = (*compare) (old, t);

  if (c < 0)

    t->left = delete_treap (old, t->left, compare);

  if (c > 0)

    t->right = delete_treap (old, t->right, compare);

  if (c == 0)

    t = delete_root (t);

  return t;

}

void

gfc_delete_bbt (void *root, void *old, compare_fn compare)

{

  gfc_bbt **t;

  t = (gfc_bbt **) root;

  *t = delete_treap ((gfc_bbt *) old, *t, compare);

}