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33 * @(#)in_cksum.c 8.1 (Berkeley) 6/10/93
34 * $FreeBSD: src/sys/netinet/in_cksum.c,v 1.6 1999/08/28 00:49:16 peter Exp $
35 * $DragonFly: src/sys/netinet/in_cksum.c,v 1.3 2003/07/26 21:00:04 rob Exp $
38 #include <sys/param.h>
42 * Checksum routine for Internet Protocol family headers (Portable Version).
44 * This routine is very heavily used in the network
45 * code and should be modified for each CPU to be as fast as possible.
48 #define ADDCARRY(x) (x > 65535 ? x -= 65535 : x)
49 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
70 for (;m && len; m = m->m_next) {
73 w = mtod(m, u_short *);
76 * The first byte of this mbuf is the continuation
77 * of a word spanning between this mbuf and the
80 * s_util.c[0] is already saved when scanning previous
83 s_util.c[1] = *(char *)w;
85 w = (u_short *)((char *)w + 1);
94 * Force to even boundary.
96 if ((1 & (int) w) && (mlen > 0)) {
99 s_util.c[0] = *(u_char *)w;
100 w = (u_short *)((char *)w + 1);
105 * Unroll the loop to make overhead from
108 while ((mlen -= 32) >= 0) {
109 sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
110 sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
111 sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
112 sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
116 while ((mlen -= 8) >= 0) {
117 sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
121 if (mlen == 0 && byte_swapped == 0)
124 while ((mlen -= 2) >= 0) {
132 s_util.c[1] = *(char *)w;
137 } else if (mlen == -1)
138 s_util.c[0] = *(char *)w;
141 printf("cksum: out of data\n");
143 /* The last mbuf has odd # of bytes. Follow the
144 standard (the odd byte may be shifted left by 8 bits
145 or not as determined by endian-ness of the machine) */
150 return (~sum & 0xffff);