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

/*      $NetBSD: tsearch.c,v 1.3 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: tsearch.c,v 1.3 1999/09/16 11:45:37 lukem Exp $");
#endif /* LIBC_SCCS and not lint */
#endif
__FBSDID("$FreeBSD: src/lib/libc/stdlib/tsearch.c,v 1.4 2003/01/05 02:43:18 tjr Exp $");

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

/* find or insert datum into search tree */
void *
tsearch(vkey, vrootp, compar)
        const void *vkey;               /* key to be located */
        void **vrootp;                  /* address of tree root */
        int (*compar)(const void *, const void *);
{
        node_t *q;
        node_t **rootp = (node_t **)vrootp;

        if (rootp == NULL)
                return NULL;

        while (*rootp != NULL) {        /* Knuth's T1: */
                int r;

                if ((r = (*compar)(vkey, (*rootp)->key)) == 0)  /* T2: */
                        return *rootp;          /* we found it! */

                rootp = (r < 0) ?
                    &(*rootp)->llink :          /* T3: follow left branch */
                    &(*rootp)->rlink;           /* T4: follow right branch */
        }

        q = malloc(sizeof(node_t));             /* T5: key not found */
        if (q != 0) {                           /* make new node */
                *rootp = q;                     /* link new node to old */
                /* LINTED const castaway ok */
                q->key = (void *)vkey;          /* initialize new node */
                q->llink = q->rlink = NULL;
        }
        return q;
}