// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   *
   * 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.

   */
  
  /* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access
   kills, so most of the assembly has to go. */

  #include <linux/export.h>

  #include <net/checksum.h>
  
  #include <asm/byteorder.h>

  #ifndef do_csum

  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;
  }

  #endif

  #ifndef ip_fast_csum

  /*
   *	This is a version of ip_compute_csum() optimized for IP headers,
   *	which always checksum on 4 octet boundaries.
   */
  __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
  {
  	return (__force __sum16)~do_csum(iph, ihl*4);
  }
  EXPORT_SYMBOL(ip_fast_csum);

  #endif

  
  /*
   * 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);

  #ifndef csum_tcpudp_nofold

  static inline u32 from64to32(u64 x)
  {
  	/* add up 32-bit and 32-bit for 32+c bit */
  	x = (x & 0xffffffff) + (x >> 32);
  	/* add up carry.. */
  	x = (x & 0xffffffff) + (x >> 32);
  	return (u32)x;
  }

  __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,

  			  __u32 len, __u8 proto, __wsum sum)

  {
  	unsigned long long s = (__force u32)sum;
  
  	s += (__force u32)saddr;
  	s += (__force u32)daddr;
  #ifdef __BIG_ENDIAN
  	s += proto + len;
  #else
  	s += (proto + len) << 8;
  #endif

  	return (__force __wsum)from64to32(s);

  }
  EXPORT_SYMBOL(csum_tcpudp_nofold);
  #endif