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