2 * Copyright (c) 2003,2004 The DragonFly Project. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
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34 * $DragonFly: src/sys/netinet/in_cksum.c,v 1.9 2005/01/06 09:14:13 hsu Exp $
37 #include <sys/param.h>
38 #include <sys/systm.h>
40 #include <sys/in_cksum.h>
42 #include <netinet/in.h>
43 #include <netinet/in_systm.h>
44 #include <netinet/ip.h>
45 #include <netinet/ip_var.h>
47 #include <machine/endian.h>
50 * Return the 16 bit 1's complement checksum in network byte order. Devolve
51 * the mbuf into 32 bit aligned segments that we can pass to assembly and
52 * do the rest manually. Even though we return a 16 bit unsigned value,
53 * we declare it as a 32 bit unsigned value to reduce unnecessary assembly
56 * Byte ordering issues. Note two things. First, no secondary carry occurs,
57 * and second, a one's complement checksum is endian-independant. If we are
58 * given a data buffer in network byte order, our checksum will be in network
61 * 0xffff + 0xffff = 0xfffe + C = 0xffff (so no second carry occurs).
63 * 0x8142 + 0x8243 = 0x0385 + C = 0x0386 (checksum is in same byte order
64 * 0x4281 + 0x4382 = 0x8603 as the data regardless of arch)
66 * This works with 16, 32, 64, etc... bits as long as we deal with the
67 * carry when collapsing it back down to 16 bits.
71 in_cksum_range(struct mbuf *m, int nxt, int offset, int bytes)
88 if (offset < sizeof(struct ipovly))
89 panic("in_cksum_range: offset too short");
90 if (m->m_len < sizeof(struct ip))
91 panic("in_cksum_range: bad mbuf chain");
92 bzero(&ipov, sizeof ipov);
93 ipov.ih_len = htons(bytes);
95 ipov.ih_src = mtod(m, struct ip *)->ip_src;
96 ipov.ih_dst = mtod(m, struct ip *)->ip_dst;
97 ptr = (uint8_t *)&ipov;
99 sum32 = asm_ones32(ptr, sizeof(ipov) / 4);
100 sum32 = (sum32 >> 16) + (sum32 & 0xffff);
108 * Skip fully engulfed mbufs. Branch predict optimal.
110 while (m && offset >= m->m_len) {
116 * Process the checksum for each segment. Note that the code below is
117 * branch-predict optimal, so it's faster then you might otherwise
118 * believe. When we are buffer-aligned but also odd-byte-aligned from
119 * the point of view of the IP packet, we accumulate to sum1 instead of
122 * Initial offsets do not pre-set flip (assert that offset is even?)
124 while (bytes > 0 && m) {
126 * Calculate pointer base and number of bytes to snarf, account
129 ptr = mtod(m, __uint8_t *) + offset;
130 if ((n = m->m_len - offset) > bytes)
135 * First 16-bit-align our buffer by eating a byte if necessary,
136 * then 32-bit-align our buffer by eating a word if necessary.
138 * We are endian-sensitive when chomping a byte. WARNING! Be
139 * careful optimizing this! 16 ane 32 bit words must be aligned
140 * for this to be generic code.
142 if (((intptr_t)ptr & 1) && n) {
143 #if BYTE_ORDER == LITTLE_ENDIAN
158 if (((intptr_t)ptr & 2) && n > 1) {
160 sum1 += *(__uint16_t *)ptr;
162 sum0 += *(__uint16_t *)ptr;
168 * Process a 32-bit aligned data buffer and accumulate the result
169 * in sum0 or sum1. Allow only one 16 bit overflow carry.
174 sum32 = asm_ones32((void *)ptr, n >> 2);
175 sum32 = (sum32 >> 16) + (sum32 & 0xffff);
181 /* n &= 3; dontcare */
185 * Handle oddly-sized buffers. Handle word issues first while
186 * ptr is still aligned.
190 sum1 += *(__uint16_t *)ptr;
192 sum0 += *(__uint16_t *)ptr;
194 /* n -= 2; dontcare */
197 #if BYTE_ORDER == LITTLE_ENDIAN
208 /* ++ptr; dontcare */
217 * Due to byte aligned or oddly-sized buffers we may have a checksum
218 * in sum1 which needs to be shifted and added to our main sum. There
219 * is a presumption here that no more then 255 overflows occured which
220 * is 255/3 byte aligned mbufs in the worst case.
223 sum0 = (sum0 >> 16) + (sum0 & 0xffff);
226 return(~sum0 & 0xffff);