text: /*
   *
   * 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 <linux/module.h>
  #include <net/checksum.h>
  
  #include <asm/byteorder.h>
  
  static inline unsigned short from32to16(unsigned int 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 int do_csum(const unsigned char *buff, int len)
  {
  	int odd;
  	unsigned int result = 0;
  
  	if (len <= 0)
  		goto out;
  	odd = 1 & (unsigned long) buff;
  	if (odd) {
  #ifdef __LITTLE_ENDIAN
  		result += (*buff << 8);
  #else
  		result = *buff;
  #endif
  		len--;
  		buff++;
  	}
  	if (len >= 2) {
  		if (2 & (unsigned long) buff) {
  			result += *(unsigned short *) buff;
  			len -= 2;
  			buff += 2;
  		}
  		if (len >= 4) {
  			const unsigned char *end = buff + ((unsigned)len & ~3);
  			unsigned int carry = 0;
  			do {
  				unsigned int w = *(unsigned int *) buff;
  				buff += 4;
  				result += carry;
  				result += w;
  				carry = (w > result);
  			} while (buff < end);
  			result += carry;
  			result = (result & 0xffff) + (result >> 16);
  		}
  		if (len & 2) {
  			result += *(unsigned short *) buff;
  			buff += 2;
  		}
  	}
  	if (len & 1)
  #ifdef __LITTLE_ENDIAN
  		result += *buff;
  #else
  		result += (*buff << 8);
  #endif
  	result = from32to16(result);
  	if (odd)
  		result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
  out:
  	return result;
  }
  EXPORT_SYMBOL(ip_fast_csum);
  
  /*
   * 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
   */
  __wsum csum_partial(const void *buff, int len, __wsum wsum)
  {
  	unsigned int sum = (__force unsigned int)wsum;
  	unsigned int result = do_csum(buff, len);
  
  	/* add in old sum, and carry.. */
  	result += sum;
  	if (sum > result)
  		result += 1;
  	return (__force __wsum)result;
  }
  EXPORT_SYMBOL(csum_partial);
  
  /*
   * this routine is used for miscellaneous IP-like checksums, mainly
   * in icmp.c
   */
  __sum16 ip_compute_csum(const void *buff, int len)
  {
  	return (__force __sum16)~do_csum(buff, len);
  }
  EXPORT_SYMBOL(ip_compute_csum);
  
  /*
   * copy from fs while checksumming, otherwise like csum_partial
   */
  __wsum
  csum_partial_copy_from_user(const void __user *src, void *dst, int len,
  						__wsum sum, int *csum_err)
  {
  	int missing;
  
  	missing = __copy_from_user(dst, src, len);
  	if (missing) {
  		memset(dst + len - missing, 0, missing);
  		*csum_err = -EFAULT;
  	} else
  		*csum_err = 0;
  
  	return csum_partial(dst, len, sum);
  }
  EXPORT_SYMBOL(csum_partial_copy_from_user);
  
  /*
   * copy from ds while checksumming, otherwise like csum_partial
   */
  __wsum
  csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
  {
  	memcpy(dst, src, len);
  	return csum_partial(dst, len, sum);
  }
  EXPORT_SYMBOL(csum_partial_copy);
  