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.
   *
   *		Checksumming functions for IP, TCP, UDP and so on
   *
   * Authors:	Jorge Cwik, <jorge@laser.satlink.net>
   *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
   *		Borrows very liberally from tcp.c and ip.c, see those
   *		files for more names.
   *
   *		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.
   */
  
  #ifndef _CHECKSUM_H
  #define _CHECKSUM_H
  
  #include <linux/errno.h>
  #include <asm/types.h>
  #include <asm/byteorder.h>
  #include <linux/uaccess.h>
  #include <asm/checksum.h>
  
  #ifndef _HAVE_ARCH_COPY_AND_CSUM_FROM_USER
  static inline
  __wsum csum_and_copy_from_user (const void __user *src, void *dst,
  				      int len, __wsum sum, int *err_ptr)
  {
  	if (access_ok(src, len))
  		return csum_partial_copy_from_user(src, dst, len, sum, err_ptr);
  
  	if (len)
  		*err_ptr = -EFAULT;
  
  	return sum;
  }
  #endif
  
  #ifndef HAVE_CSUM_COPY_USER
  static __inline__ __wsum csum_and_copy_to_user
  (const void *src, void __user *dst, int len, __wsum sum, int *err_ptr)
  {
  	sum = csum_partial(src, len, sum);
  
  	if (access_ok(dst, len)) {
  		if (copy_to_user(dst, src, len) == 0)
  			return sum;
  	}
  	if (len)
  		*err_ptr = -EFAULT;
  
  	return (__force __wsum)-1; /* invalid checksum */
  }
  #endif
  
  #ifndef HAVE_ARCH_CSUM_ADD
  static inline __wsum csum_add(__wsum csum, __wsum addend)
  {
  	u32 res = (__force u32)csum;
  	res += (__force u32)addend;
  	return (__force __wsum)(res + (res < (__force u32)addend));
  }
  #endif
  
  static inline __wsum csum_sub(__wsum csum, __wsum addend)
  {
  	return csum_add(csum, ~addend);
  }
  
  static inline __sum16 csum16_add(__sum16 csum, __be16 addend)
  {
  	u16 res = (__force u16)csum;
  
  	res += (__force u16)addend;
  	return (__force __sum16)(res + (res < (__force u16)addend));
  }
  
  static inline __sum16 csum16_sub(__sum16 csum, __be16 addend)
  {
  	return csum16_add(csum, ~addend);
  }
  
  static inline __wsum
  csum_block_add(__wsum csum, __wsum csum2, int offset)
  {
  	u32 sum = (__force u32)csum2;
  
  	/* rotate sum to align it with a 16b boundary */
  	if (offset & 1)
  		sum = ror32(sum, 8);
  
  	return csum_add(csum, (__force __wsum)sum);
  }
  
  static inline __wsum
  csum_block_add_ext(__wsum csum, __wsum csum2, int offset, int len)
  {
  	return csum_block_add(csum, csum2, offset);
  }
  
  static inline __wsum
  csum_block_sub(__wsum csum, __wsum csum2, int offset)
  {
  	return csum_block_add(csum, ~csum2, offset);
  }
  
  static inline __wsum csum_unfold(__sum16 n)
  {
  	return (__force __wsum)n;
  }
  
  static inline __wsum csum_partial_ext(const void *buff, int len, __wsum sum)
  {
  	return csum_partial(buff, len, sum);
  }
  
  #define CSUM_MANGLED_0 ((__force __sum16)0xffff)
  
  static inline void csum_replace_by_diff(__sum16 *sum, __wsum diff)
  {
  	*sum = csum_fold(csum_add(diff, ~csum_unfold(*sum)));
  }
  
  static inline void csum_replace4(__sum16 *sum, __be32 from, __be32 to)
  {
  	__wsum tmp = csum_sub(~csum_unfold(*sum), (__force __wsum)from);
  
  	*sum = csum_fold(csum_add(tmp, (__force __wsum)to));
  }
  
  /* Implements RFC 1624 (Incremental Internet Checksum)
   * 3. Discussion states :
   *     HC' = ~(~HC + ~m + m')
   *  m : old value of a 16bit field
   *  m' : new value of a 16bit field
   */
  static inline void csum_replace2(__sum16 *sum, __be16 old, __be16 new)
  {
  	*sum = ~csum16_add(csum16_sub(~(*sum), old), new);
  }
  
  struct sk_buff;
  void inet_proto_csum_replace4(__sum16 *sum, struct sk_buff *skb,
  			      __be32 from, __be32 to, bool pseudohdr);
  void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb,
  			       const __be32 *from, const __be32 *to,
  			       bool pseudohdr);
  void inet_proto_csum_replace_by_diff(__sum16 *sum, struct sk_buff *skb,
  				     __wsum diff, bool pseudohdr);
  
  static inline void inet_proto_csum_replace2(__sum16 *sum, struct sk_buff *skb,
  					    __be16 from, __be16 to,
  					    bool pseudohdr)
  {
  	inet_proto_csum_replace4(sum, skb, (__force __be32)from,
  				 (__force __be32)to, pseudohdr);
  }
  
  static inline __wsum remcsum_adjust(void *ptr, __wsum csum,
  				    int start, int offset)
  {
  	__sum16 *psum = (__sum16 *)(ptr + offset);
  	__wsum delta;
  
  	/* Subtract out checksum up to start */
  	csum = csum_sub(csum, csum_partial(ptr, start, 0));
  
  	/* Set derived checksum in packet */
  	delta = csum_sub((__force __wsum)csum_fold(csum),
  			 (__force __wsum)*psum);
  	*psum = csum_fold(csum);
  
  	return delta;
  }
  
  static inline void remcsum_unadjust(__sum16 *psum, __wsum delta)
  {
  	*psum = csum_fold(csum_sub(delta, (__force __wsum)*psum));
  }
  
  #endif
  