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Member "tin-2.4.5/src/hashstr.c" (1 Dec 2020, 3910 Bytes) of package /linux/misc/tin-2.4.5.tar.xz:


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    1 /*
    2  *  Project   : tin - a Usenet reader
    3  *  Module    : hashstr.c
    4  *  Author    : I. Lea & R. Skrenta
    5  *  Created   : 1991-04-01
    6  *  Updated   : 2020-05-13
    7  *  Notes     :
    8  *
    9  * Copyright (c) 1991-2021 Iain Lea <iain@bricbrac.de>, Rich Skrenta <skrenta@pbm.com>
   10 
   11  * All rights reserved.
   12  *
   13  * Redistribution and use in source and binary forms, with or without
   14  * modification, are permitted provided that the following conditions
   15  * are met:
   16  *
   17  * 1. Redistributions of source code must retain the above copyright notice,
   18  *    this list of conditions and the following disclaimer.
   19  *
   20  * 2. Redistributions in binary form must reproduce the above copyright
   21  *    notice, this list of conditions and the following disclaimer in the
   22  *    documentation and/or other materials provided with the distribution.
   23  *
   24  * 3. Neither the name of the copyright holder nor the names of its
   25  *    contributors may be used to endorse or promote products derived from
   26  *    this software without specific prior written permission.
   27  *
   28  * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   29  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   31  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
   32  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   33  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   34  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   35  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   36  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   37  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   38  * POSSIBILITY OF SUCH DAMAGE.
   39  */
   40 
   41 
   42 #ifndef TIN_H
   43 #   include "tin.h"
   44 #endif /* !TIN_H */
   45 
   46 /*
   47  * Maintain a table of all strings we have seen.
   48  * If a new string comes in, add it to the table and return a pointer
   49  * to it. If we've seen it before, just return the pointer to it.
   50  *
   51  *  Usage: hash_str("some string") returns char *
   52  *
   53  * Spillovers are chained on the end
   54  */
   55 
   56 static struct t_hashnode *table[HASHNODE_TABLE_SIZE];
   57 static struct t_hashnode *add_string(const char *s);
   58 
   59 char *
   60 hash_str(
   61     const char *s)
   62 {
   63     const unsigned char *t = (const unsigned char *) s;
   64     int len = 0;
   65     long h;             /* result of hash: index into hash table */
   66     struct t_hashnode **p;  /* used to descend the spillover structs */
   67 
   68     if (s == NULL)
   69         return NULL;
   70 
   71     h = 0;
   72     while (*t) {
   73         h = (h << 1) ^ *t++;
   74         if (++len & 7)
   75             continue;
   76         h %= (long) HASHNODE_TABLE_SIZE;
   77     }
   78     h %= (long) HASHNODE_TABLE_SIZE;
   79 
   80     p = &table[h];
   81 
   82     while (*p) {
   83         if (STRCMPEQ(s, (*p)->txt))
   84             return (*p)->txt;
   85         p = &(*p)->next;
   86     }
   87 
   88     *p = add_string(s);
   89     return (*p)->txt;           /* Return ptr to text, _not_ the struct */
   90 }
   91 
   92 
   93 /*
   94  * Add a string to the hash table
   95  * Each entry will have the following structure:
   96  *
   97  * t_hashnode *next     Pointer to the next hashnode in chain
   98  * int aptr                 'magic' ptr used to speed subj threading
   99  * T                            The text itself. The ptr that hash_str()
  100  * E                            returns points here - the earlier fields
  101  * X                            are 'hidden'.
  102  * T
  103  * \0                           String terminator
  104  */
  105 static struct t_hashnode *
  106 add_string(
  107     const char *s)
  108 {
  109     struct t_hashnode *p;
  110 
  111     p = my_malloc(sizeof(struct t_hashnode) + strlen(s));
  112 
  113     p->next = (struct t_hashnode *) 0;
  114     p->aptr = -1;                   /* -1 is the default value */
  115 
  116     strcpy(p->txt, s);          /* Copy in the text */
  117 
  118     return p;
  119 }
  120 
  121 
  122 void
  123 hash_init(
  124     void)
  125 {
  126     int i;
  127 
  128     for (i = 0; i < HASHNODE_TABLE_SIZE; i++)
  129         table[i] = (struct t_hashnode *) 0;
  130 }
  131 
  132 
  133 void
  134 hash_reclaim(
  135     void)
  136 {
  137     int i;
  138     struct t_hashnode *p, *next;
  139 
  140     for (i = 0; i < HASHNODE_TABLE_SIZE; i++) {
  141         if (table[i] != NULL) {
  142             p = table[i];
  143             while (p != NULL) {
  144                 next = p->next;
  145                 free(p);
  146                 p = next;
  147             }
  148             table[i] = (struct t_hashnode *) 0;
  149         }
  150     }
  151 }