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Annotation of embedaddon/quagga/isisd/iso_checksum.c, revision 1.1.1.1

1.1       misho       1: /*
                      2:  * IS-IS Rout(e)ing protocol - iso_checksum.c
                      3:  *                             ISO checksum related routines
                      4:  *
                      5:  * Copyright (C) 2001,2002   Sampo Saaristo
                      6:  *                           Tampere University of Technology      
                      7:  *                           Institute of Communications Engineering
                      8:  *
                      9:  * This program is free software; you can redistribute it and/or modify it 
                     10:  * under the terms of the GNU General Public Licenseas published by the Free 
                     11:  * Software Foundation; either version 2 of the License, or (at your option) 
                     12:  * any later version.
                     13:  *
                     14:  * This program is distributed in the hope that it will be useful,but WITHOUT 
                     15:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
                     16:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for 
                     17:  * more details.
                     18: 
                     19:  * You should have received a copy of the GNU General Public License along 
                     20:  * with this program; if not, write to the Free Software Foundation, Inc., 
                     21:  * 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
                     22:  */
                     23: 
                     24: #include <zebra.h>
                     25: #include "iso_checksum.h"
                     26: #include "checksum.h"
                     27: 
                     28: /*
                     29:  * Calculations of the OSI checksum.
                     30:  * ISO/IEC 8473 defines the sum as
                     31:  *
                     32:  *     L
                     33:  *  sum  a (mod 255) = 0
                     34:  *     1  i
                     35:  *
                     36:  *     L 
                     37:  *  sum (L-i+1)a (mod 255) = 0
                     38:  *     1        i
                     39:  *
                     40:  */
                     41: 
                     42: /*
                     43:  * Verifies that the checksum is correct.
                     44:  * Return 0 on correct and 1 on invalid checksum.
                     45:  * Based on Annex C.4 of ISO/IEC 8473
                     46:  */
                     47: 
                     48: int
                     49: iso_csum_verify (u_char * buffer, int len, uint16_t * csum)
                     50: {
                     51:   u_int16_t checksum;
                     52:   u_int32_t c0;
                     53:   u_int32_t c1;
                     54: 
                     55:   c0 = *csum & 0xff00;
                     56:   c1 = *csum & 0x00ff;
                     57: 
                     58:   /*
                     59:    * If both are zero return correct
                     60:    */
                     61:   if (c0 == 0 && c1 == 0)
                     62:     return 0;
                     63: 
                     64:   /*
                     65:    * If either, but not both are zero return incorrect
                     66:    */
                     67:   if (c0 == 0 || c1 == 0)
                     68:     return 1;
                     69: 
                     70:   /* Offset of checksum from the start of the buffer */
                     71:   int offset = (u_char *) csum - buffer;
                     72: 
                     73:   checksum = fletcher_checksum(buffer, len, offset);
                     74:   if (checksum == *csum)
                     75:     return 0;
                     76:   return 1;
                     77: }