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Annotation of embedaddon/quagga/isisd/iso_checksum.c, revision 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: }