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tdelete.c revision 1.4 
      1 /*	$NetBSD: tdelete.c,v 1.4 2006/03/19 01:12:08 christos Exp $	*/
      2 
      3 /*
      4  * Tree search generalized from Knuth (6.2.2) Algorithm T just like
      5  * the AT&T man page says.
      6  *
      7  * The node_t structure is for internal use only, lint doesn't grok it.
      8  *
      9  * Written by reading the System V Interface Definition, not the code.
     10  *
     11  * Totally public domain.
     12  */
     13 
     14 #include <sys/cdefs.h>
     15 #if defined(LIBC_SCCS) && !defined(lint)
     16 __RCSID("$NetBSD: tdelete.c,v 1.4 2006/03/19 01:12:08 christos Exp $");
     17 #endif /* LIBC_SCCS and not lint */
     18 
     19 #include <assert.h>
     20 #define _SEARCH_PRIVATE
     21 #include <search.h>
     22 #include <stdlib.h>
     23 
     24 
     25 /* delete node with given key */
     26 void *
     27 tdelete(vkey, vrootp, compar)
     28 	const void *vkey;	/* key to be deleted */
     29 	void      **vrootp;	/* address of the root of tree */
     30 	int       (*compar) __P((const void *, const void *));
     31 {
     32 	node_t **rootp = (node_t **)vrootp;
     33 	node_t *p, *q, *r;
     34 	int  cmp;
     35 
     36 	_DIAGASSERT(vkey != NULL);
     37 	_DIAGASSERT(compar != NULL);
     38 
     39 	if (rootp == NULL || (p = *rootp) == NULL)
     40 		return NULL;
     41 
     42 	while ((cmp = (*compar)(vkey, (*rootp)->key)) != 0) {
     43 		p = *rootp;
     44 		rootp = (cmp < 0) ?
     45 		    &(*rootp)->llink :		/* follow llink branch */
     46 		    &(*rootp)->rlink;		/* follow rlink branch */
     47 		if (*rootp == NULL)
     48 			return NULL;		/* key not found */
     49 	}
     50 	r = (*rootp)->rlink;			/* D1: */
     51 	if ((q = (*rootp)->llink) == NULL)	/* Left NULL? */
     52 		q = r;
     53 	else if (r != NULL) {			/* Right link is NULL? */
     54 		if (r->llink == NULL) {		/* D2: Find successor */
     55 			r->llink = q;
     56 			q = r;
     57 		} else {			/* D3: Find NULL link */
     58 			for (q = r->llink; q->llink != NULL; q = r->llink)
     59 				r = q;
     60 			r->llink = q->rlink;
     61 			q->llink = (*rootp)->llink;
     62 			q->rlink = (*rootp)->rlink;
     63 		}
     64 	}
     65 	if (p != *rootp)
     66 		free(*rootp);			/* D4: Free node */
     67 	*rootp = q;				/* link parent to new node */
     68 	return p;
     69 }
     70