/* * INET		An implementation of the TCP/IP protocol suite for the LINUX *		operating system.  INET is implemented using the  BSD Socket *		interface as the means of communication with the user level. * *		IP/TCP/UDP checksumming routines * * Authors:	Jorge Cwik, <jorge@laser.satlink.net> *		Arnt Gulbrandsen, <agulbra@nvg.unit.no> *		Tom May, <ftom@netcom.com> *		Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de> *		Lots of code moved from tcp.c and ip.c; see those files *		for more names. * * 03/02/96	Jes Sorensen, Andreas Schwab, Roman Hodek: *		Fixed some nasty bugs, causing some horrible crashes. *		A: At some points, the sum (%0) was used as *		length-counter instead of the length counter *		(%1). Thanks to Roman Hodek for pointing this out. *		B: GCC seems to mess up if one uses too many *		data-registers to hold input values and one tries to *		specify d0 and d1 as scratch registers. Letting gcc choose these *      registers itself solves the problem. * *		This program is free software; you can redistribute it and/or *		modify it under the terms of the GNU General Public License *		as published by the Free Software Foundation; either version *		2 of the License, or (at your option) any later version. */ /* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access kills, so most   of the assembly has to go. */#include <net/checksum.h>static inline unsigned short from32to16(unsigned long x){	/* add up 16-bit and 16-bit for 16+c bit */	x = (x & 0xffff) + (x >> 16);	/* add up carry.. */	x = (x & 0xffff) + (x >> 16);	return x;}static unsigned long do_csum(const unsigned char * buff, int len){	int odd, count;	unsigned long result = 0;	if (len <= 0)		goto out;	odd = 1 & (unsigned long) buff;	if (odd) {		result = *buff;		len--;		buff++;	}	count = len >> 1;		/* nr of 16-bit words.. */	if (count) {		if (2 & (unsigned long) buff) {			result += *(unsigned short *) buff;			count--;			len -= 2;			buff += 2;		}		count >>= 1;		/* nr of 32-bit words.. */		if (count) {		        unsigned long carry = 0;			do {				unsigned long w = *(unsigned long *) buff;				count--;				buff += 4;				result += carry;				result += w;				carry = (w > result);			} while (count);			result += carry;			result = (result & 0xffff) + (result >> 16);		}		if (len & 2) {			result += *(unsigned short *) buff;			buff += 2;		}	}	if (len & 1)		result += (*buff << 8);	result = from32to16(result);	if (odd)		result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);out:	return result;}/* *	This is a version of ip_compute_csum() optimized for IP headers, *	which always checksum on 4 octet boundaries. */unsigned short ip_fast_csum(unsigned char * iph, unsigned int ihl){	return ~do_csum(iph,ihl*4);}/* * computes the checksum of a memory block at buff, length len, * and adds in "sum" (32-bit) * * returns a 32-bit number suitable for feeding into itself * or csum_tcpudp_magic * * this function must be called with even lengths, except * for the last fragment, which may be odd * * it's best to have buff aligned on a 32-bit boundary */unsigned int csum_partial(const unsigned char * buff, int len, unsigned int sum){	unsigned int result = do_csum(buff, len);	/* add in old sum, and carry.. */	result += sum;	/* 16+c bits -> 16 bits */	result = (result & 0xffff) + (result >> 16);	return result;}/* * this routine is used for miscellaneous IP-like checksums, mainly * in icmp.c */unsigned short ip_compute_csum(const unsigned char * buff, int len){	return ~do_csum(buff,len);}/* * copy from fs while checksumming, otherwise like csum_partial */unsigned intcsum_partial_copy_fromuser(const char *src, char *dst, int len, int sum){	memcpy(dst, src, len);	return csum_partial(dst, len, sum);}/* * copy from ds while checksumming, otherwise like csum_partial */unsigned intcsum_partial_copy(const char *src, char *dst, int len, int sum){	memcpy(dst, src, len);	return csum_partial(dst, len, sum);}