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tdelete.c

/*    $NetBSD: tdelete.c,v 1.3 1999/09/20 04:39:43 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 <assert.h>
#define _SEARCH_PRIVATE
#include <search.h>
#include <stdlib.h>

#define _DIAGASSERT assert



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

      _DIAGASSERT(compar != NULL);

      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;
}

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