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/*************************************************
* xfpt - Simple ASCII->Docbook processor *
*************************************************/
/* Copyright (c) University of Cambridge, 2006 */
/* Written by Philip Hazel. */
/* This module contains tree management routines. A tree is used for locally
defined entity values. */
#include "xfpt.h"
/***********************************************************
* Binary Balanced Tree Management Routines *
***********************************************************/
/* This set of routines maintains a balanced binary tree using
the algorithm given in Knuth Vol 3 page 455.
The routines make use of uschar * pointers as byte pointers,
so as to be able to do arithmetic on them, since ANSI Standard
C does not permit additions and subtractions on void pointers. */
/*************************************************
* Flags and Parameters *
*************************************************/
#define tree_lbal 1 /* left subtree is longer */
#define tree_rbal 2 /* right subtree is longer */
#define tree_bmask 3 /* mask for flipping bits */
/*************************************************
* Insert a new node into a tree *
*************************************************/
/* The node->name field must (obviously) be set, but the other
fields need not be initialized.
Arguments:
treebase pointer to the root of the tree
node the note to insert, with name field set
Returns: TRUE if node inserted; FALSE if not (duplicate)
*/
int
tree_insertnode(tree_node **treebase, tree_node *node)
{
tree_node *p = *treebase;
tree_node **q, *r, *s, **t;
int a;
node->left = node->right = NULL;
node->balance = 0;
/* Deal with an empty tree */
if (p == NULL)
{
*treebase = node;
return TRUE;
}
/* The tree is not empty. While finding the insertion point,
q points to the pointer to p, and t points to the pointer to
the potential re-balancing point. */
q = treebase;
t = q;
/* Loop to search tree for place to insert new node */
for (;;)
{
int c = Ustrcmp(node->name, p->name);
if (c == 0) return FALSE; /* Duplicate node encountered */
/* Deal with climbing down the tree, exiting from the loop
when we reach a leaf. */
q = (c > 0)? &(p->right) : &(p->left);
p = *q;
if (p == NULL) break;
/* Save the address of the pointer to the last node en route
which has a non-zero balance factor. */
if (p->balance != 0) t = q;
}
/* When the above loop completes, q points to the pointer to NULL;
that is the place at which the new node must be inserted. */
*q = node;
/* Set up s as the potential re-balancing point, and r as the
next node after it along the route. */
s = *t;
r = (Ustrcmp(node->name, s->name) > 0)? s->right : s->left;
/* Adjust balance factors along the route from s to node. */
p = r;
while (p != node)
{
if (Ustrcmp(node->name, p->name) < 0)
{
p->balance = tree_lbal;
p = p->left;
}
else
{
p->balance = tree_rbal;
p = p->right;
}
}
/* Now the World-Famous Balancing Act */
a = (Ustrcmp(node->name, s->name) < 0)? tree_lbal : tree_rbal;
if (s->balance == 0) s->balance = (uschar)a; /* The tree has grown higher */
else if (s->balance != (uschar)a) s->balance = 0; /* It's become more balanced */
else /* It's got out of balance */
{
/* Perform a single rotation */
if (r->balance == (uschar)a)
{
p = r;
if (a == tree_rbal)
{
s->right = r->left;
r->left = s;
}
else
{
s->left = r->right;
r->right = s;
}
s->balance = 0;
r->balance = 0;
}
/* Perform a double rotation There was an occasion when the balancing
factors were screwed up by a bug in the code that reads a tree from
the spool. In case this ever happens again, check for changing p to NULL
and don't do it. It is better to have an unbalanced tree than a crash. */
else
{
if (a == tree_rbal)
{
if (r->left == NULL) return TRUE; /* Bail out if tree corrupt */
p = r->left;
r->left = p->right;
p->right = r;
s->right = p->left;
p->left = s;
}
else
{
if (r->right == NULL) return TRUE; /* Bail out if tree corrupt */
p = r->right;
r->right = p->left;
p->left = r;
s->left = p->right;
p->right = s;
}
s->balance = (p->balance == (uschar)a)? (uschar)(a^tree_bmask) : 0;
r->balance = (p->balance == (uschar)(a^tree_bmask))? (uschar)a : 0;
p->balance = 0;
}
/* Finishing touch */
*t = p;
}
return TRUE; /* Successful insertion */
}
/*************************************************
* Search tree for node by name *
*************************************************/
/*
Arguments:
p root of tree
name key to search for
Returns: pointer to node, or NULL if not found
*/
tree_node *
tree_search(tree_node *p, uschar *name)
{
while (p != NULL)
{
int c = Ustrcmp(name, p->name);
if (c == 0) return p;
p = (c < 0)? p->left : p->right;
}
return NULL;
}
/* End of tree.c */
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