diff options
Diffstat (limited to '')
| -rw-r--r-- | in_cksum.c | 200 |
1 files changed, 200 insertions, 0 deletions
diff --git a/in_cksum.c b/in_cksum.c new file mode 100644 index 0000000..eb7c634 --- /dev/null +++ b/in_cksum.c @@ -0,0 +1,200 @@ +/* in_cksum.c + * 4.4-Lite-2 Internet checksum routine, modified to take a vector of + * pointers/lengths giving the pieces to be checksummed. Also using + * Tahoe/CGI version of ADDCARRY(x) macro instead of from portable version. + */ + +/* + * Copyright (c) 1988, 1992, 1993 + * The Regents of the University of California. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. Neither the name of the University nor the names of its contributors + * may be used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + * + * @(#)in_cksum.c 8.1 (Berkeley) 6/10/93 + */ + +#ifdef HAVE_CONFIG_H +# include <config.h> +#endif + +#include "netdissect-stdinc.h" + +#include "netdissect.h" + +/* + * Checksum routine for Internet Protocol family headers (Portable Version). + * + * This routine is very heavily used in the network + * code and should be modified for each CPU to be as fast as possible. + */ + +#define ADDCARRY(x) {if ((x) > 65535) (x) -= 65535;} +#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);} + +uint16_t +in_cksum(const struct cksum_vec *vec, int veclen) +{ + const uint16_t *w; + int sum = 0; + int mlen = 0; + int byte_swapped = 0; + + union { + uint8_t c[2]; + uint16_t s; + } s_util; + union { + uint16_t s[2]; + uint32_t l; + } l_util; + + for (; veclen != 0; vec++, veclen--) { + if (vec->len == 0) + continue; + w = (const uint16_t *)(const void *)vec->ptr; + if (mlen == -1) { + /* + * The first byte of this chunk is the continuation + * of a word spanning between this chunk and the + * last chunk. + * + * s_util.c[0] is already saved when scanning previous + * chunk. + */ + s_util.c[1] = *(const uint8_t *)w; + sum += s_util.s; + w = (const uint16_t *)(const void *)((const uint8_t *)w + 1); + mlen = vec->len - 1; + } else + mlen = vec->len; + /* + * Force to even boundary. + */ + if ((1 & (uintptr_t) w) && (mlen > 0)) { + REDUCE; + sum <<= 8; + s_util.c[0] = *(const uint8_t *)w; + w = (const uint16_t *)(const void *)((const uint8_t *)w + 1); + mlen--; + byte_swapped = 1; + } + /* + * Unroll the loop to make overhead from + * branches &c small. + */ + while ((mlen -= 32) >= 0) { + sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; + sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7]; + sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11]; + sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15]; + w += 16; + } + mlen += 32; + while ((mlen -= 8) >= 0) { + sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; + w += 4; + } + mlen += 8; + if (mlen == 0 && byte_swapped == 0) + continue; + REDUCE; + while ((mlen -= 2) >= 0) { + sum += *w++; + } + if (byte_swapped) { + REDUCE; + sum <<= 8; + byte_swapped = 0; + if (mlen == -1) { + s_util.c[1] = *(const uint8_t *)w; + sum += s_util.s; + mlen = 0; + } else + mlen = -1; + } else if (mlen == -1) + s_util.c[0] = *(const uint8_t *)w; + } + if (mlen == -1) { + /* The last mbuf has odd # of bytes. Follow the + standard (the odd byte may be shifted left by 8 bits + or not as determined by endian-ness of the machine) */ + s_util.c[1] = 0; + sum += s_util.s; + } + REDUCE; + return (~sum & 0xffff); +} + +/* + * Given the host-byte-order value of the checksum field in a packet + * header, and the network-byte-order computed checksum of the data + * that the checksum covers (including the checksum itself), compute + * what the checksum field *should* have been. + */ +uint16_t +in_cksum_shouldbe(uint16_t sum, uint16_t computed_sum) +{ + uint32_t shouldbe; + + /* + * The value that should have gone into the checksum field + * is the negative of the value gotten by summing up everything + * *but* the checksum field. + * + * We can compute that by subtracting the value of the checksum + * field from the sum of all the data in the packet, and then + * computing the negative of that value. + * + * "sum" is the value of the checksum field, and "computed_sum" + * is the negative of the sum of all the data in the packets, + * so that's -(-computed_sum - sum), or (sum + computed_sum). + * + * All the arithmetic in question is one's complement, so the + * addition must include an end-around carry; we do this by + * doing the arithmetic in 32 bits (with no sign-extension), + * and then adding the upper 16 bits of the sum, which contain + * the carry, to the lower 16 bits of the sum, and then do it + * again in case *that* sum produced a carry. + * + * As RFC 1071 notes, the checksum can be computed without + * byte-swapping the 16-bit words; summing 16-bit words + * on a big-endian machine gives a big-endian checksum, which + * can be directly stuffed into the big-endian checksum fields + * in protocol headers, and summing words on a little-endian + * machine gives a little-endian checksum, which must be + * byte-swapped before being stuffed into a big-endian checksum + * field. + * + * "computed_sum" is a network-byte-order value, so we must put + * it in host byte order before subtracting it from the + * host-byte-order value from the header; the adjusted checksum + * will be in host byte order, which is what we'll return. + */ + shouldbe = sum; + shouldbe += ntohs(computed_sum); + shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16); + shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16); + return (uint16_t)shouldbe; +} |