FreeBSD/Linux Kernel Cross Reference
sys/i386/include/in_cksum.h

     /*-
      * Copyright (c) 1990 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
     *      from:           @(#)in_cksum.c  1.3 (Berkeley) 1/19/91
     *      from: Id: in_cksum.c,v 1.8 1995/12/03 18:35:19 bde Exp
     * $FreeBSD: src/sys/i386/include/in_cksum.h,v 1.2.2.1 1999/09/05 08:11:50 peter Exp $
     */
    
    #ifndef _MACHINE_IN_CKSUM_H_
    #define _MACHINE_IN_CKSUM_H_    1
    
    #include <sys/cdefs.h>
    
    /*
     * It it useful to have an Internet checksum routine which is inlineable
     * and optimized specifically for the task of computing IP header checksums
     * in the normal case (where there are no options and the header length is
     * therefore always exactly five 32-bit words.
     */
    #ifdef __GNUC__
    static __inline u_int
    in_cksum_hdr(const struct ip *ip)
    {
            register u_int sum = 0;
                        
    #define ADD(n)  __asm("addl " #n "(%2), %0" : "=r" (sum) : "" (sum), "r" (ip))
    #define ADDC(n) __asm("adcl " #n "(%2), %0" : "=r" (sum) : "" (sum), "r" (ip))
    #define MOP     __asm("adcl         $0, %0" : "=r" (sum) : "" (sum))
    
            ADD(0);
            ADDC(4);
            ADDC(8);
            ADDC(12);
            ADDC(16);
            MOP;
            sum = (sum & 0xffff) + (sum >> 16);
            if (sum > 0xffff)
                    sum -= 0xffff;
    
            return ~sum & 0xffff;
    }
    
    static __inline void
    in_cksum_update(struct ip *ip)
    {
            int __tmpsum;
            __tmpsum = (int)ntohs(ip->ip_sum) + 256;
            ip->ip_sum = htons(__tmpsum + (__tmpsum >> 16));
    }
    
    #else
    u_int in_cksum_hdr __P((const struct ip *));
    #define in_cksum_update(ip) \
            do { \
                    int __tmpsum; \
                    __tmpsum = (int)ntohs(ip->ip_sum) + 256; \
                    ip->ip_sum = htons(__tmpsum + (__tmpsum >> 16)); \
            } while(0)
    
    #endif
    
    #endif /* _MACHINE_IN_CKSUM_H_ */

Cache object: a6092a0f3a2d3ae8cb523fa57c7e0641