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29 * @(#)in_cksum.c 8.1 (Berkeley) 6/10/93
30 * in_cksum.c,v 1.2 1994/08/02 07:48:16 davidg Exp
36 * Checksum routine for Internet Protocol family headers (Portable Version).
38 * This routine is very heavily used in the network
39 * code and should be modified for each CPU to be as fast as possible.
41 * XXX Since we will never span more than 1 mbuf, we can optimise this
44 #define ADDCARRY(x) (x > 65535 ? x -= 65535 : x)
45 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; \
48 int cksum(struct mbuf *m, int len)
52 register int mlen = 0;
66 w = mtod(m, uint16_t *);
76 * Force to even boundary.
78 if ((1 & (uintptr_t)w) && (mlen > 0)) {
81 s_util.c[0] = *(uint8_t *)w;
82 w = (uint16_t *)((int8_t *)w + 1);
87 * Unroll the loop to make overhead from
90 while ((mlen -= 32) >= 0) {
91 sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
92 sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
93 sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
94 sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
98 while ((mlen -= 8) >= 0) {
99 sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
103 if (mlen == 0 && byte_swapped == 0)
106 while ((mlen -= 2) >= 0) {
114 s_util.c[1] = *(uint8_t *)w;
120 } else if (mlen == -1)
121 s_util.c[0] = *(uint8_t *)w;
126 DEBUG_ERROR((dfd, "cksum: out of data\n"));
127 DEBUG_ERROR((dfd, " len = %d\n", len));
131 /* The last mbuf has odd # of bytes. Follow the
132 standard (the odd byte may be shifted left by 8 bits
133 or not as determined by endian-ness of the machine) */
138 return (~sum & 0xffff);