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
     * $FreeBSD$
     */
    
    #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;
    
    /* __volatile is necessary here because the condition codes are used. */
    #define ADD(n)  __asm __volatile ("addl %1, %0" : "+r" (sum) : \
        "g" (((const u_int32_t *)ip)[n / 4]))
    #define ADDC(n) __asm __volatile ("adcl %1, %0" : "+r" (sum) : \
        "g" (((const u_int32_t *)ip)[n / 4]))
    #define MOP     __asm __volatile ("adcl $0, %0" : "+r" (sum))
    
            ADD(0);
            ADDC(4);
            ADDC(8);
            ADDC(12);
            ADDC(16);
            MOP;
    #undef ADD
    #undef ADDC
    #undef 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));
    }
    
    static __inline u_short
    in_addword(u_short sum, u_short b)
    {
            /* __volatile is necessary because the condition codes are used. */
            __asm __volatile ("addw %1, %0" : "+r" (sum) : "r" (b));
            __asm __volatile ("adcw $0, %0" : "+r" (sum));
    
            return (sum);
    }
    
    static __inline u_short
    in_pseudo(u_int sum, u_int b, u_int c)
    {
           /* __volatile is necessary because the condition codes are used. */
           __asm __volatile ("addl %1, %0" : "+r" (sum) : "g" (b));
           __asm __volatile ("adcl %1, %0" : "+r" (sum) : "g" (c));
           __asm __volatile ("adcl $0, %0" : "+r" (sum));
   
           sum = (sum & 0xffff) + (sum >> 16);
           if (sum > 0xffff)
                   sum -= 0xffff;
           return (sum);
   }
   
   #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
   
   typedef unsigned in_psum_t;
   #ifdef _KERNEL
   u_short in_cksum_skip(struct mbuf *m, int len, int skip); 
   in_psum_t in_cksum_partial(in_psum_t psum, const u_short *w, int len);
   int     in_cksum_finalize(in_psum_t psum);
   #endif /* _KERNEL */
   
   #endif /* _MACHINE_IN_CKSUM_H_ */

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