tsearch/tsearch.c

   1 /*      $NetBSD: tsearch.c,v 1.4 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
  20 /* find or insert datum into search tree */
  21 void *
  22 tsearch(const void * __restrict__ vkey,         /* key to be located */
  23         void ** __restrict__ vrootp,            /* address of tree root */
  24         int (*compar) (const void *, const void *))
  25 {
  26         node_t *q;
  27         node_t **rootp = (node_t **)vrootp;
  28
  29         if (rootp == NULL)
  30                 return NULL;
  31
  32         while (*rootp != NULL) {        /* Knuth's T1: */
  33                 int r;
  34
  35                 if ((r = (*compar)(vkey, (*rootp)->key)) == 0)  /* T2: */
  36                         return *rootp;          /* we found it! */
  37
  38                 rootp = (r < 0) ?
  39                     &(*rootp)->llink :          /* T3: follow left branch */
  40                     &(*rootp)->rlink;           /* T4: follow right branch */
  41         }
  42
  43         q = malloc(sizeof(node_t));             /* T5: key not found */
  44         if (q != 0) {                           /* make new node */
  45                 *rootp = q;                     /* link new node to old */
  46                 /* LINTED const castaway ok */
  47                 q->key = (void *)vkey;          /* initialize new node */
  48                 q->llink = q->rlink = NULL;
  49         }
  50         return q;
  51 }