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Annotation of 43BSDTahoe/etc/timed/cksum.m68000.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1983 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution and use in source and binary forms are permitted
        !             6:  * provided that the above copyright notice and this paragraph are
        !             7:  * duplicated in all such forms and that any documentation,
        !             8:  * advertising materials, and other materials related to such
        !             9:  * distribution and use acknowledge that the software was developed
        !            10:  * by the University of California, Berkeley.  The name of the
        !            11:  * University may not be used to endorse or promote products derived
        !            12:  * from this software without specific prior written permission.
        !            13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            15:  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            16:  */
        !            17: 
        !            18: #ifndef lint
        !            19: static char sccsid[] = "@(#)cksum.m68000.c     2.3 (Berkeley) 6/18/88";
        !            20: #endif /* not lint */
        !            21: 
        !            22: #include "../globals.h"
        !            23: #include <protocols/timed.h>
        !            24: 
        !            25: /* computes the checksum for ip packets for a Motorola 68000 base computer */
        !            26: 
        !            27: in_cksum(w, mlen)
        !            28:        register u_short *w;
        !            29:        register int mlen;
        !            30: {
        !            31:        register int sum = 0;
        !            32: 
        !            33:        if (mlen > 0) {
        !            34:                if (((int)w & 1) == 0) {
        !            35:                        sum = ocsum(w, mlen>>1);
        !            36:                        w += mlen>>1;
        !            37:                        if (mlen & 1) {
        !            38:                                sum += *(u_char *)w << 8;
        !            39:                                mlen = -1;
        !            40:                        }
        !            41:                } else {
        !            42:                        u_short swsum;
        !            43: 
        !            44:                        sum = *(u_char *)w << 8;
        !            45:                        mlen--;
        !            46:                        w = (u_short *)(1 + (int)w);
        !            47:                        swsum = ocsum(w, mlen>>1);
        !            48:                        swab((char *)&swsum, (char *)&swsum, sizeof swsum);
        !            49:                        sum += swsum;
        !            50:                        w += mlen>>1;
        !            51:                        if (mlen & 1)
        !            52:                                sum += *(u_char *)w;
        !            53:                }
        !            54:        }
        !            55:        sum = (sum & 0xFFFF) + (sum >> 16);
        !            56:        sum = (sum & 0xFFFF) + (sum >> 16);
        !            57:        sum = (~sum) & 0xFFFF;
        !            58:        return (sum);
        !            59: }

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