/*
 * Copyright (c) 1988, 1992, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)in_cksum.c  8.1 (Berkeley) 6/10/93
 * $Id: NetIPChecksum.c 2922 2007-03-19 16:48:52Z baderma $
 */

/* Modified for TOPSY by David Schweikert */

#include "NetBuf.h"
#include "NetDebug.h"

/*
 * Checksum routine for Internet Protocol family headers (Portable Version).
 *
 * This routine is very heavily used in the network
 * code and should be modified for each CPU to be as fast as possible.
 */

#define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}

int netipChecksum(NetBuf buf, int len)
{
  unsigned short *w;
  int sum = 0;
  int buflen = 0;
  int byte_swapped = 0;

  union {
    char    c[2];
    unsigned short s;
  } s_util;
  union {
    unsigned short s[2];
    long    l;
  } l_util;

  for (;buf && len; buf = buf->next)
  {
    if (buf->start == buf->end)
      continue;

    w = (unsigned short *) NETBUF_DATA(buf);

    if (buflen == -1)
    {
      /*
       * The first byte of this netbuf is the continuation
       * of a word spanning between this netbuf and the
       * last netbuf.
       *
       * s_util.c[0] is already saved when scanning previous
       * netbuf.
       */
      s_util.c[1] = *(char *)w;
      sum += s_util.s;
      w = (unsigned short *)((char *)w + 1);
      buflen = NETBUF_LEN(buf) - 1;
      len--;
    }
    else
    {
      buflen = NETBUF_LEN(buf);
    }

    if (len < buflen)
      buflen = len;
    len -= buflen;
    /*
     * Force to even boundary.
     */
    if ((1 & (int) w) && (buflen > 0))
    {
      REDUCE;
      sum <<= 8;
      s_util.c[0] = *(unsigned char *)w;
      w = (unsigned short *)((char *)w + 1);
      buflen--;
      byte_swapped = 1;
    }
    /*
     * Unroll the loop to make overhead from
     * branches &c small.
     */
    while ((buflen -= 32) >= 0)
    {
      sum += w[0];
      sum += w[1];
      sum += w[2];
      sum += w[3];
      sum += w[4];
      sum += w[5];
      sum += w[6];
      sum += w[7];
      sum += w[8];
      sum += w[9];
      sum += w[10];
      sum += w[11];
      sum += w[12];
      sum += w[13];
      sum += w[14];
      sum += w[15];
      w += 16;
    }
    buflen += 32;
    while ((buflen -= 8) >= 0)
    {
      sum += w[0];
      sum += w[1];
      sum += w[2];
      sum += w[3];
      w += 4;
    }
    buflen += 8;
    if (buflen == 0 && byte_swapped == 0)
      continue;
    REDUCE;
    while ((buflen -= 2) >= 0)
    {
      sum += *w++;
    }
    if (byte_swapped)
    {
      REDUCE;
      sum <<= 8;
      byte_swapped = 0;
      if (buflen == -1)
      {
        s_util.c[1] = *(char *)w;
        sum += s_util.s;
        buflen = 0;
      }
      else
      {
        buflen = -1;
      }
    }
    else if (buflen == -1)
    {
      s_util.c[0] = *(char *)w;
    }
  }
  if (len)
    netdbgDisplay(NETDEBUG_GENERIC, "netip : cksum: out of data.\n");
  if (buflen == -1)
  {
    /* The last netbuf has odd # of bytes. Follow the
       standard (the odd byte may be shifted left by 8 bits
       or not as determined by endian-ness of the machine) */
    s_util.c[1] = 0;
    sum += s_util.s;
  }
  REDUCE;
  return (~sum & 0xffff);
}
