lib/krb5/crc.c

   1 /*
   2  * Copyright (c) 1997 - 2000 Kungliga Tekniska Högskolan
   3  * (Royal Institute of Technology, Stockholm, Sweden).
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  *
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  *
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  *
  17  * 3. Neither the name of the Institute nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  */
  33
  34 #include "krb5_locl.h"
  35
  36 static u_long table[256];
  37
  38 #define CRC_GEN 0xEDB88320L
  39
  40 void
  41 _krb5_crc_init_table(void)
  42 {
  43     static int flag = 0;
  44     unsigned long crc, poly;
  45     unsigned int i, j;
  46
  47     if(flag) return;
  48     poly = CRC_GEN;
  49     for (i = 0; i < 256; i++) {
  50         crc = i;
  51         for (j = 8; j > 0; j--) {
  52             if (crc & 1) {
  53                 crc = (crc >> 1) ^ poly;
  54             } else {
  55                 crc >>= 1;
  56             }
  57         }
  58         table[i] = crc;
  59     }
  60     flag = 1;
  61 }
  62
  63 uint32_t
  64 _krb5_crc_update (const char *p, size_t len, uint32_t res)
  65 {
  66     while (len--)
  67         res = table[(res ^ *p++) & 0xFF] ^ (res >> 8);
  68     return res & 0xFFFFFFFF;
  69 }