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Annotation of 43BSD/etc/timed/m68000/cksum.c, revision 1.1.1.1

1.1       root        1: /*
                      2:  * Copyright (c) 1983 Regents of the University of California.
                      3:  * All rights reserved.  The Berkeley software License Agreement
                      4:  * specifies the terms and conditions for redistribution.
                      5:  */
                      6: 
                      7: #ifndef lint
                      8: static char sccsid[] = "@(#)cksum.c    2.1 (Berkeley) 6/6/86";
                      9: #endif not lint
                     10: 
                     11: #include "../globals.h"
                     12: #include <protocols/timed.h>
                     13: 
                     14: /* computes the checksum for ip packets for a Motorola 68000 base computer */
                     15: 
                     16: in_cksum(w, mlen)
                     17:        register u_short *w;
                     18:        register int mlen;
                     19: {
                     20:        register int sum = 0;
                     21: 
                     22:        if (mlen > 0) {
                     23:                if (((int)w & 1) == 0) {
                     24:                        sum = ocsum(w, mlen>>1);
                     25:                        w += mlen>>1;
                     26:                        if (mlen & 1) {
                     27:                                sum += *(u_char *)w << 8;
                     28:                                mlen = -1;
                     29:                        }
                     30:                } else {
                     31:                        u_short swsum;
                     32: 
                     33:                        sum = *(u_char *)w << 8;
                     34:                        mlen--;
                     35:                        w = (u_short *)(1 + (int)w);
                     36:                        swsum = ocsum(w, mlen>>1);
                     37:                        swab((char *)&swsum, (char *)&swsum, sizeof swsum);
                     38:                        sum += swsum;
                     39:                        w += mlen>>1;
                     40:                        if (mlen & 1)
                     41:                                sum += *(u_char *)w;
                     42:                }
                     43:        }
                     44:        sum = (sum & 0xFFFF) + (sum >> 16);
                     45:        sum = (sum & 0xFFFF) + (sum >> 16);
                     46:        sum = (~sum) & 0xFFFF;
                     47:        return (sum);
                     48: }

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