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Annotation of researchv9/sys/inet/vecadd.c, revision 1.1.1.1

1.1       root        1: #include "../h/param.h"
                      2: 
                      3: /*
                      4:  * Compute a 16 bit checksum for the internet.
                      5:  * This routine will only work on a 68020 as it assumes
                      6:  * a short pointer can be used to access odd addresses.
                      7:  * If odd is set, reverse the bytes in the sum.
                      8:  */
                      9: vecadd(w, len, sum, odd)
                     10: register u_short *w;
                     11: register int len;
                     12: register u_long sum;
                     13: int odd;
                     14: {
                     15:        register u_char *c;
                     16:        int extra;
                     17: 
                     18:        if (odd) {
                     19:                c = (u_char *)w;
                     20:                sum += *c++;
                     21:                w = (u_short *)c;
                     22:                len--;
                     23:        }
                     24:        extra = (int)len & 1;
                     25:        len >>= 1;
                     26:        while (len--)
                     27:                sum += *w++;
                     28:        if (extra) {
                     29:                c = (u_char *)w;
                     30:                sum += *c << 8;
                     31:        }
                     32:        sum = (sum >> 16) + (sum & 0xffff);
                     33:        /* Check for a carry */
                     34:        if (sum & 0x10000)
                     35:                sum = (sum & ~0x10000) + 1;
                     36:        return (sum);
                     37: }

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