/*
   * This file was originally taken from the FreeBSD project.
   *
   * Copyright (c) 2001 Charles Mott <cm@linktel.net>
   * Copyright (c) 2008 coresystems GmbH
   * All rights reserved.
   *
   * SPDX-License-Identifier:	BSD-2-Clause
   */
  
  #include <common.h>
  #include <net.h>
  
  unsigned compute_ip_checksum(const void *vptr, unsigned nbytes)
  {
  	int sum, oddbyte;
  	const unsigned short *ptr = vptr;
  
  	sum = 0;
  	while (nbytes > 1) {
  		sum += *ptr++;
  		nbytes -= 2;
  	}
  	if (nbytes == 1) {
  		oddbyte = 0;
  		((u8 *)&oddbyte)[0] = *(u8 *)ptr;
  		((u8 *)&oddbyte)[1] = 0;
  		sum += oddbyte;
  	}
  	sum = (sum >> 16) + (sum & 0xffff);
  	sum += (sum >> 16);
  	sum = ~sum & 0xffff;
  
  	return sum;
  }
  
  unsigned add_ip_checksums(unsigned offset, unsigned sum, unsigned new)
  {
  	unsigned long checksum;
  
  	sum = ~sum & 0xffff;
  	new = ~new & 0xffff;
  	if (offset & 1) {
  		/*
  		 * byte-swap the sum if it came from an odd offset; since the
  		 * computation is endian independant this works.
  		 */
  		new = ((new >> 8) & 0xff) | ((new << 8) & 0xff00);
  	}
  	checksum = sum + new;
  	if (checksum > 0xffff)
  		checksum -= 0xffff;
  
  	return (~checksum) & 0xffff;
  }
  
  int ip_checksum_ok(const void *addr, unsigned nbytes)
  {
  	return !(compute_ip_checksum(addr, nbytes) & 0xfffe);
  }