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33 * @(#)ns_cksum.c 8.1 (Berkeley) 6/10/93
37 #include <sys/param.h>
41 * Checksum routine for Network Systems Protocol Packets (Big-Endian).
43 * This routine is very heavily used in the network
44 * code and should be modified for each CPU to be as fast as possible.
47 #define ADDCARRY(x) { if ((x) > 65535) (x) -= 65535; }
48 #define FOLD(x) {l_util.l = (x); (x) = l_util.s[0] + l_util.s[1]; ADDCARRY(x);}
52 register struct mbuf *m;
57 register int mlen = 0;
65 for (;m && len; m = m->m_next) {
69 * Each trip around loop adds in
70 * word from one mbuf segment.
72 w = mtod(m, u_short *);
75 * There is a byte left from the last segment;
76 * ones-complement add it into the checksum.
78 #if BYTE_ORDER == BIG_ENDIAN
81 sum += *(u_char *)w << 8;
84 w = (u_short *)(1 + (char *)w);
94 * We can do a 16 bit ones complement sum using
95 * 32 bit arithmetic registers for adding,
96 * with carries from the low added
97 * into the high (by normal carry-chaining)
98 * so long as we fold back before 16 carries have occured.
103 /* -DTINY reduces the size from 1250 to 550, but slows it down by 22% */
104 while ((mlen -= 32) >= 0) {
105 sum += w[0]; sum += sum; sum += w[1]; sum += sum;
106 sum += w[2]; sum += sum; sum += w[3]; sum += sum;
107 sum += w[4]; sum += sum; sum += w[5]; sum += sum;
108 sum += w[6]; sum += sum; sum += w[7]; sum += sum;
110 sum += w[8]; sum += sum; sum += w[9]; sum += sum;
111 sum += w[10]; sum += sum; sum += w[11]; sum += sum;
112 sum += w[12]; sum += sum; sum += w[13]; sum += sum;
113 sum += w[14]; sum += sum; sum += w[15]; sum += sum;
119 while ((mlen -= 8) >= 0) {
120 sum += w[0]; sum += sum; sum += w[1]; sum += sum;
121 sum += w[2]; sum += sum; sum += w[3]; sum += sum;
126 while ((mlen -= 2) >= 0) {
127 sum += *w++; sum += sum;
131 #if BYTE_ORDER == BIG_ENDIAN
132 #define ww(n) (((u_char *)w)[n + n + 1])
133 #define vv(n) (((u_char *)w)[n + n])
135 #if BYTE_ORDER == LITTLE_ENDIAN
136 #define vv(n) (((u_char *)w)[n + n + 1])
137 #define ww(n) (((u_char *)w)[n + n])
142 while ((mlen -= 32) >= 0) {
143 sum += ww(0); sum += sum; sum += ww(1); sum += sum;
144 sum += ww(2); sum += sum; sum += ww(3); sum += sum;
145 sum += ww(4); sum += sum; sum += ww(5); sum += sum;
146 sum += ww(6); sum += sum; sum += ww(7); sum += sum;
148 sum += ww(8); sum += sum; sum += ww(9); sum += sum;
149 sum += ww(10); sum += sum; sum += ww(11); sum += sum;
150 sum += ww(12); sum += sum; sum += ww(13); sum += sum;
151 sum += ww(14); sum += sum; sum += ww(15); sum += sum;
153 sum2 += vv(0); sum2 += sum2; sum2 += vv(1); sum2 += sum2;
154 sum2 += vv(2); sum2 += sum2; sum2 += vv(3); sum2 += sum2;
155 sum2 += vv(4); sum2 += sum2; sum2 += vv(5); sum2 += sum2;
156 sum2 += vv(6); sum2 += sum2; sum2 += vv(7); sum2 += sum2;
158 sum2 += vv(8); sum2 += sum2; sum2 += vv(9); sum2 += sum2;
159 sum2 += vv(10); sum2 += sum2; sum2 += vv(11); sum2 += sum2;
160 sum2 += vv(12); sum2 += sum2; sum2 += vv(13); sum2 += sum2;
161 sum2 += vv(14); sum2 += sum2; sum2 += vv(15); sum2 += sum2;
167 while ((mlen -= 8) >= 0) {
168 sum += ww(0); sum += sum; sum += ww(1); sum += sum;
169 sum += ww(2); sum += sum; sum += ww(3); sum += sum;
171 sum2 += vv(0); sum2 += sum2; sum2 += vv(1); sum2 += sum2;
172 sum2 += vv(2); sum2 += sum2; sum2 += vv(3); sum2 += sum2;
177 while ((mlen -= 2) >= 0) {
178 sum += ww(0); sum += sum;
179 sum2 += vv(0); sum2 += sum2;
185 #if BYTE_ORDER == BIG_ENDIAN
186 sum += *(u_char *)w << 8;
194 /* We had an odd number of bytes to sum; assume a garbage
195 byte of zero and clean up */
200 * sum has already been kept to low sixteen bits.
201 * just examine result and exit.
203 if(sum==0xffff) sum = 0;