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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8 * modification, are permitted provided that the following conditions
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34 * $DragonFly: src/sys/netinet/in_cksum.c,v 1.5 2004/07/16 05:51:19 dillon 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>
46 #include <machine/endian.h>
49 * Return the 16 bit 1's complement checksum in network byte order. Devolve
50 * the mbuf into 32 bit aligned segments that we can pass to assembly and
51 * do the rest manually. Even though we return a 16 bit unsigned value,
52 * we declare it as a 32 bit unsigned value to reduce unnecessary assembly
55 * Byte ordering issues. Note two things. First, no secondary carry occurs,
56 * and second, a one's complement checksum is endian-independant. If we are
57 * given a data buffer in network byte order, our checksum will be in network
60 * 0xffff + 0xffff = 0xfffe + C = 0xffff (so no second carry occurs).
62 * 0x8142 + 0x8243 = 0x0385 + C = 0x0386 (checksum is in same byte order
63 * 0x4281 + 0x4382 = 0x8603 as the data regardless of arch)
65 * This works with 16, 32, 64, etc... bits as long as we deal with the
66 * carry when collapsing it back down to 16 bits.
69 in_cksum_range(struct mbuf *m, int offset, int bytes)
78 * Skip fully engulfed mbufs. Branch predict optimal.
80 while (m && offset >= m->m_len) {
86 * Process the checksum for each segment. Note that the code below is
87 * branch-predict optimal, so it's faster then you might otherwise
88 * believe. When we are buffer-aligned but also odd-byte-aligned from
89 * the point of view of the IP packet, we accumulate to sum1 instead of
92 * Initial offsets do not pre-set flip (assert that offset is even?)
97 while (bytes > 0 && m) {
99 * Calculate pointer base and number of bytes to snarf, account
102 ptr = mtod(m, __uint8_t *) + offset;
103 if ((n = m->m_len - offset) > bytes)
108 * First 16-bit-align our buffer by eating a byte if necessary,
109 * then 32-bit-align our buffer by eating a word if necessary.
111 * We are endian-sensitive when chomping a byte. WARNING! Be
112 * careful optimizing this! 16 ane 32 bit words must be aligned
113 * for this to be generic code.
115 if (((intptr_t)ptr & 1) && n) {
116 #if BYTE_ORDER == LITTLE_ENDIAN
131 if (((intptr_t)ptr & 2) && n > 1) {
133 sum1 += *(__uint16_t *)ptr;
135 sum0 += *(__uint16_t *)ptr;
141 * Process a 32-bit aligned data buffer and accumulate the result
142 * in sum0 or sum1. Allow only one 16 bit overflow carry.
147 sum32 = asm_ones32((void *)ptr, n >> 2);
148 sum32 = (sum32 >> 16) + (sum32 & 0xffff);
154 /* n &= 3; dontcare */
158 * Handle oddly-sized buffers. Handle word issues first while
159 * ptr is still aligned.
163 sum1 += *(__uint16_t *)ptr;
165 sum0 += *(__uint16_t *)ptr;
167 /* n -= 2; dontcare */
170 #if BYTE_ORDER == LITTLE_ENDIAN
181 /* ++ptr; dontcare */
190 * Due to byte aligned or oddly-sized buffers we may have a checksum
191 * in sum1 which needs to be shifted and added to our main sum. There
192 * is a presumption here that no more then 255 overflows occured which
193 * is 255/3 byte aligned mbufs in the worst case.
196 sum0 = (sum0 >> 16) + (sum0 & 0xffff);
199 return(~sum0 & 0xffff);