text: /* SPDX-License-Identifier: GPL-2.0 */
  #ifndef __ASM_GENERIC_CHECKSUM_H
  #define __ASM_GENERIC_CHECKSUM_H
  
  /*
   * 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
   */
  extern __wsum csum_partial(const void *buff, int len, __wsum sum);
  
  /*
   * the same as csum_partial, but copies from src while it
   * checksums
   *
   * here even more important to align src and dst on a 32-bit (or even
   * better 64-bit) boundary
   */
  #ifndef csum_partial_copy_nocheck
  __wsum csum_partial_copy_nocheck(const void *src, void *dst, int len,
  		__wsum sum);
  #endif
  
  #ifndef ip_fast_csum
  /*
   * This is a version of ip_compute_csum() optimized for IP headers,
   * which always checksum on 4 octet boundaries.
   */
  extern __sum16 ip_fast_csum(const void *iph, unsigned int ihl);
  #endif
  
  #ifndef csum_fold
  /*
   * Fold a partial checksum
   */
  static inline __sum16 csum_fold(__wsum csum)
  {
  	u32 sum = (__force u32)csum;
  	sum = (sum & 0xffff) + (sum >> 16);
  	sum = (sum & 0xffff) + (sum >> 16);
  	return (__force __sum16)~sum;
  }
  #endif
  
  #ifndef csum_tcpudp_nofold
  /*
   * computes the checksum of the TCP/UDP pseudo-header
   * returns a 16-bit checksum, already complemented
   */
  extern __wsum
  csum_tcpudp_nofold(__be32 saddr, __be32 daddr, __u32 len,
  		   __u8 proto, __wsum sum);
  #endif
  
  #ifndef csum_tcpudp_magic
  static inline __sum16
  csum_tcpudp_magic(__be32 saddr, __be32 daddr, __u32 len,
  		  __u8 proto, __wsum sum)
  {
  	return csum_fold(csum_tcpudp_nofold(saddr, daddr, len, proto, sum));
  }
  #endif
  
  /*
   * this routine is used for miscellaneous IP-like checksums, mainly
   * in icmp.c
   */
  extern __sum16 ip_compute_csum(const void *buff, int len);
  
  #endif /* __ASM_GENERIC_CHECKSUM_H */
  