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74 lines
1.8 KiB
C
74 lines
1.8 KiB
C
/*
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* IS-IS Rout(e)ing protocol - iso_checksum.c
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* ISO checksum related routines
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*
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* Copyright (C) 2001,2002 Sampo Saaristo
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* Tampere University of Technology
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* Institute of Communications Engineering
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public Licenseas published by the Free
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* Software Foundation; either version 2 of the License, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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* more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; see the file COPYING; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <zebra.h>
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#include "iso_checksum.h"
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#include "checksum.h"
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/*
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* Calculations of the OSI checksum.
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* ISO/IEC 8473 defines the sum as
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*
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* L
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* sum a (mod 255) = 0
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* 1 i
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*
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* L
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* sum (L-i+1)a (mod 255) = 0
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* 1 i
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*
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*/
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/*
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* Verifies that the checksum is correct.
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* Return 0 on correct and 1 on invalid checksum.
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* Based on Annex C.4 of ISO/IEC 8473
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*/
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int iso_csum_verify(u_char *buffer, int len, uint16_t csum, int offset)
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{
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u_int16_t checksum;
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u_int32_t c0;
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u_int32_t c1;
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c0 = csum & 0xff00;
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c1 = csum & 0x00ff;
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/*
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* If both are zero return correct
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*/
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if (c0 == 0 && c1 == 0)
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return 0;
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/*
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* If either, but not both are zero return incorrect
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*/
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if (c0 == 0 || c1 == 0)
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return 1;
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checksum = fletcher_checksum(buffer, len, offset);
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if (checksum == htons(csum))
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return 0;
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return 1;
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}
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