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29 * @(#)in_cksum.c 8.1 (Berkeley) 6/10/93
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
35 #include <sys/param.h>
39 * Checksum routine for Internet Protocol family headers (Portable Version).
41 * This routine is very heavily used in the network
42 * code and should be modified for each CPU to be as fast as possible.
45 #define ADDCARRY(x) (x > 65535 ? x -= 65535 : x)
46 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
49 in_cksum(struct mbuf *m, int len)
53 register int mlen = 0;
65 for (;m && len; m = m->m_next) {
68 w = mtod(m, u_short *);
71 * The first byte of this mbuf is the continuation
72 * of a word spanning between this mbuf and the
75 * s_util.c[0] is already saved when scanning previous
78 s_util.c[1] = *(char *)w;
80 w = (u_short *)((char *)w + 1);
89 * Force to even boundary.
91 if ((1 & (uintptr_t) w) && (mlen > 0)) {
94 s_util.c[0] = *(u_char *)w;
95 w = (u_short *)((char *)w + 1);
100 * Unroll the loop to make overhead from
103 while ((mlen -= 32) >= 0) {
104 sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
105 sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
106 sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
107 sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
111 while ((mlen -= 8) >= 0) {
112 sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
116 if (mlen == 0 && byte_swapped == 0)
119 while ((mlen -= 2) >= 0) {
127 s_util.c[1] = *(char *)w;
132 } else if (mlen == -1)
133 s_util.c[0] = *(char *)w;
136 printf("cksum: out of data\n");
138 /* The last mbuf has odd # of bytes. Follow the
139 standard (the odd byte may be shifted left by 8 bits
140 or not as determined by endian-ness of the machine) */
145 return (~sum & 0xffff);