tsearch/tdelete.c

   1 /*      $NetBSD: tdelete.c,v 1.3 1999/09/20 04:39:43 lukem 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 <assert.h>
  15 #define _SEARCH_PRIVATE
  16 #include <tsearch/search.h>
  17 #include <stdlib.h>
  18
  19 #define _DIAGASSERT assert
  20
  21
  22
  23 /* delete node with given key */
  24 void *
  25 tdelete(const void *vkey,       /* key to be deleted */
  26         void      **vrootp,     /* address of the root of tree */
  27         int       (*compar)(const void *, const void *))
  28 {
  29         node_t **rootp = (node_t **)vrootp;
  30         node_t *p, *q, *r;
  31         int  cmp;
  32
  33         _DIAGASSERT(vkey != NULL);
  34         _DIAGASSERT(compar != NULL);
  35
  36         if (rootp == NULL || (p = *rootp) == NULL)
  37                 return NULL;
  38
  39         while ((cmp = (*compar)(vkey, (*rootp)->key)) != 0) {
  40                 p = *rootp;
  41                 rootp = (cmp < 0) ?
  42                     &(*rootp)->llink :          /* follow llink branch */
  43                     &(*rootp)->rlink;           /* follow rlink branch */
  44                 if (*rootp == NULL)
  45                         return NULL;            /* key not found */
  46         }
  47         r = (*rootp)->rlink;                    /* D1: */
  48         if ((q = (*rootp)->llink) == NULL)      /* Left NULL? */
  49                 q = r;
  50         else if (r != NULL) {                   /* Right link is NULL? */
  51                 if (r->llink == NULL) {         /* D2: Find successor */
  52                         r->llink = q;
  53                         q = r;
  54                 } else {                        /* D3: Find NULL link */
  55                         for (q = r->llink; q->llink != NULL; q = r->llink)
  56                                 r = q;
  57                         r->llink = q->rlink;
  58                         q->llink = (*rootp)->llink;
  59                         q->rlink = (*rootp)->rlink;
  60                 }
  61         }
  62         free(*rootp);                           /* D4: Free node */
  63         *rootp = q;                             /* link parent to new node */
  64         return p;
  65 }