source: vendor/FreeBSD-libc/5.1/stdlib/tdelete.c

/*      $NetBSD: tdelete.c,v 1.2 1999/09/16 11:45:37 lukem Exp $        */

/*
 * Tree search generalized from Knuth (6.2.2) Algorithm T just like
 * the AT&T man page says.
 *
 * The node_t structure is for internal use only, lint doesn't grok it.
 *
 * Written by reading the System V Interface Definition, not the code.
 *
 * Totally public domain.
 */

#include <sys/cdefs.h>
#if 0
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: tdelete.c,v 1.2 1999/09/16 11:45:37 lukem Exp $");
#endif /* LIBC_SCCS and not lint */
#endif
__FBSDID("$FreeBSD: src/lib/libc/stdlib/tdelete.c,v 1.6 2003/01/05 02:43:18 tjr Exp $");

#define _SEARCH_PRIVATE
#include <search.h>
#include <stdlib.h>


/*
 * delete node with given key
 *
 * vkey:   key to be deleted
 * vrootp: address of the root of the tree
 * compar: function to carry out node comparisons
 */
void *
tdelete(const void * __restrict vkey, void ** __restrict vrootp,
    int (*compar)(const void *, const void *))
{
        node_t **rootp = (node_t **)vrootp;
        node_t *p, *q, *r;
        int cmp;

        if (rootp == NULL || (p = *rootp) == NULL)
                return NULL;

        while ((cmp = (*compar)(vkey, (*rootp)->key)) != 0) {
                p = *rootp;
                rootp = (cmp < 0) ?
                    &(*rootp)->llink :          /* follow llink branch */
                    &(*rootp)->rlink;           /* follow rlink branch */
                if (*rootp == NULL)
                        return NULL;            /* key not found */
        }
        r = (*rootp)->rlink;                    /* D1: */
        if ((q = (*rootp)->llink) == NULL)      /* Left NULL? */
                q = r;
        else if (r != NULL) {                   /* Right link is NULL? */
                if (r->llink == NULL) {         /* D2: Find successor */
                        r->llink = q;
                        q = r;
                } else {                        /* D3: Find NULL link */
                        for (q = r->llink; q->llink != NULL; q = r->llink)
                                r = q;
                        r->llink = q->rlink;
                        q->llink = (*rootp)->llink;
                        q->rlink = (*rootp)->rlink;
                }
        }
        free(*rootp);                           /* D4: Free node */
        *rootp = q;                             /* link parent to new node */
        return p;
}