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/*-
* Copyright (c) 2015 Nuxi, https://nuxi.nl/
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#define _SEARCH_PRIVATE
#include <search.h>
#include <stdbool.h>
#include <stdlib.h>
#include "tsearch_path.h"
/*
* Makes a step to the left along the binary search tree. This step is
* also saved, so it can be replayed while rebalancing.
*/
#define GO_LEFT() do { \
if ((*leaf)->balance == 0 || \
((*leaf)->balance < 0 && (*leaf)->rlink->balance == 0)) { \
/* \
* If we reach a node that is balanced, or has a child \
* in the opposite direction that is balanced, we know \
* that we won't need to perform any rotations above \
* this point. In this case rotations are always \
* capable of keeping the subtree in balance. Make \
* this the root node and reset the path. \
*/ \
rootp = leaf; \
path_init(&path); \
} \
path_taking_left(&path); \
leaf = &(*leaf)->llink; \
} while (0)
/* Makes a step to the right along the binary search tree. */
#define GO_RIGHT() do { \
if ((*leaf)->balance == 0 || \
((*leaf)->balance > 0 && (*leaf)->llink->balance == 0)) { \
rootp = leaf; \
path_init(&path); \
} \
path_taking_right(&path); \
leaf = &(*leaf)->rlink; \
} while (0)
void *
tdelete(const void *restrict key, posix_tnode **restrict rootp,
int (*compar)(const void *, const void *))
{
struct path path;
posix_tnode **leaf, *old, **n, *x, *y, *z, *result;
int cmp;
/* POSIX requires that tdelete() returns NULL if rootp is NULL. */
if (rootp == NULL)
return (NULL);
/*
* Find the leaf that needs to be removed. Return if we cannot
* find an existing entry. Keep track of the path that is taken
* to get to the node, as we will need it to adjust the
* balances.
*/
result = (posix_tnode *)1;
path_init(&path);
leaf = rootp;
for (;;) {
if (*leaf == NULL)
return (NULL);
cmp = compar(key, (*leaf)->key);
if (cmp < 0) {
result = *leaf;
GO_LEFT();
} else if (cmp > 0) {
result = *leaf;
GO_RIGHT();
} else {
break;
}
}
/* Found a matching key in the tree. Remove the node. */
if ((*leaf)->llink == NULL) {
/* Node has no left children. Replace by its right subtree. */
old = *leaf;
*leaf = old->rlink;
free(old);
} else {
/*
* Node has left children. Replace this node's key by
* its predecessor's and remove that node instead.
*/
void **keyp = &(*leaf)->key;
GO_LEFT();
while ((*leaf)->rlink != NULL)
GO_RIGHT();
old = *leaf;
*keyp = old->key;
*leaf = old->llink;
free(old);
}
/*
* Walk along the same path a second time and adjust the
* balances. Though this code looks similar to the rebalancing
* performed in tsearch(), it is not identical. We now also need
* to consider the case of outward imbalance in the right-right
* and left-left case that only exists when deleting. Hence the
* duplication of code.
*/
for (n = rootp; n != leaf;) {
if (path_took_left(&path)) {
x = *n;
if (x->balance < 0) {
y = x->rlink;
if (y->balance > 0) {
/* Right-left case. */
z = y->llink;
x->rlink = z->llink;
z->llink = x;
y->llink = z->rlink;
z->rlink = y;
*n = z;
x->balance = z->balance < 0 ? 1 : 0;
y->balance = z->balance > 0 ? -1 : 0;
z->balance = 0;
} else {
/* Right-right case. */
x->rlink = y->llink;
y->llink = x;
*n = y;
if (y->balance < 0) {
x->balance = 0;
y->balance = 0;
} else {
x->balance = -1;
y->balance = 1;
}
}
} else {
--x->balance;
}
n = &x->llink;
} else {
x = *n;
if (x->balance > 0) {
y = x->llink;
if (y->balance < 0) {
/* Left-right case. */
z = y->rlink;
y->rlink = z->llink;
z->llink = y;
x->llink = z->rlink;
z->rlink = x;
*n = z;
x->balance = z->balance > 0 ? -1 : 0;
y->balance = z->balance < 0 ? 1 : 0;
z->balance = 0;
} else {
/* Left-left case. */
x->llink = y->rlink;
y->rlink = x;
*n = y;
if (y->balance > 0) {
x->balance = 0;
y->balance = 0;
} else {
x->balance = 1;
y->balance = -1;
}
}
} else {
++x->balance;
}
n = &x->rlink;
}
}
/* Return the parent of the old entry. */
return (result);
}
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