BSD 4_4 release

[unix-history] / usr / src / sys / i386 / i386 / in_cksum.c

/*-
* Copyright (c) 1990, 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.
*
* from tahoe:  in_cksum.c      1.2     86/01/05
*      @(#)in_cksum.c  8.1 (Berkeley) 6/11/93
*/

#include <sys/param.h>
#include <sys/mbuf.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>

/*
* Checksum routine for Internet Protocol family headers.
*
* This routine is very heavily used in the network
* code and should be modified for each CPU to be as fast as possible.
* 
* This implementation is 386 version.
*/

#undef  ADDCARRY
#define ADDCARRY(sum)  {                                \
                       if (sum & 0xffff0000) {         \
                               sum &= 0xffff;          \
                               sum++;                  \
                       }                               \
               }
in_cksum(m, len)
       register struct mbuf *m;
       register int len;
{
       union word {
               char    c[2];
               u_short s;
       } u;
       register u_short *w;
       register int sum = 0;
       register int mlen = 0;

       for (;m && len; m = m->m_next) {
               if (m->m_len == 0)
                       continue;
               w = mtod(m, u_short *);
               if (mlen == -1) {
                       /*
                        * The first byte of this mbuf is the continuation
                        * of a word spanning between this mbuf and the
                        * last mbuf.
                        */

                       /* u.c[0] is already saved when scanning previous 
                        * mbuf.
                        */
                       u.c[1] = *(u_char *)w;
                       sum += u.s;
                       ADDCARRY(sum);
                       w = (u_short *)((char *)w + 1);
                       mlen = m->m_len - 1;
                       len--;
               } else
                       mlen = m->m_len;

               if (len < mlen)
                       mlen = len;
               len -= mlen;

               /*
                * add by words.
                */
               while ((mlen -= 2) >= 0) {
                       if ((int)w & 0x1) {
                               /* word is not aligned */
                               u.c[0] = *(char *)w;
                               u.c[1] = *((char *)w+1);
                               sum += u.s;
                               w++;
                       } else
                               sum += *w++;
                       ADDCARRY(sum);
               }
               if (mlen == -1)
                       /*
                        * This mbuf has odd number of bytes. 
                        * There could be a word split betwen
                        * this mbuf and the next mbuf.
                        * Save the last byte (to prepend to next mbuf).
                        */
                       u.c[0] = *(u_char *)w;
       }
       if (len)
               printf("cksum: out of data\n");
       if (mlen == -1) {
               /* The last mbuf has odd # of bytes. Follow the
                  standard (the odd byte is shifted left by 8 bits) */
               u.c[1] = 0;
               sum += u.s;
               ADDCARRY(sum);
       }
       return (~sum & 0xffff);
}