in_cksum.c - platform/external/tcpdump - Git at Google

 /* 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 shouldbe;
 }
	/* 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 shouldbe;
	}