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Annotation of sys/lib/libsa/in_cksum.c, Revision 1.1

1.1     ! nbrk        1: /*     $OpenBSD: in_cksum.c,v 1.3 2003/08/11 06:23:09 deraadt Exp $    */
        !             2: /*     $NetBSD: in_cksum.c,v 1.3 1995/04/22 13:53:48 cgd Exp $ */
        !             3:
        !             4: /*
        !             5:  * Copyright (c) 1992 Regents of the University of California.
        !             6:  * All rights reserved.
        !             7:  *
        !             8:  * This software was developed by the Computer Systems Engineering group
        !             9:  * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
        !            10:  * contributed to Berkeley.
        !            11:  *
        !            12:  * Redistribution and use in source and binary forms, with or without
        !            13:  * modification, are permitted provided that the following conditions
        !            14:  * are met:
        !            15:  * 1. Redistributions of source code must retain the above copyright
        !            16:  *    notice, this list of conditions and the following disclaimer.
        !            17:  * 2. Redistributions in binary form must reproduce the above copyright
        !            18:  *    notice, this list of conditions and the following disclaimer in the
        !            19:  *    documentation and/or other materials provided with the distribution.
        !            20:  * 3. All advertising materials mentioning features or use of this software
        !            21:  *    must display the following acknowledgement:
        !            22:  *     This product includes software developed by the University of
        !            23:  *     California, Lawrence Berkeley Laboratory and its contributors.
        !            24:  * 4. Neither the name of the University nor the names of its contributors
        !            25:  *    may be used to endorse or promote products derived from this software
        !            26:  *    without specific prior written permission.
        !            27:  *
        !            28:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            29:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            30:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            31:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            32:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            33:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            34:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            35:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            36:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            37:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            38:  * SUCH DAMAGE.
        !            39:  *
        !            40:  * @(#) Header: in_cksum.c,v 1.1 92/09/11 01:15:55 leres Exp  (LBL)
        !            41:  */
        !            42:
        !            43: #include <sys/types.h>
        !            44: #include <sys/socket.h>
        !            45: #include <net/if.h>
        !            46: #include <netinet/in.h>
        !            47:
        !            48: #include <netinet/if_ether.h>
        !            49: #include <netinet/in_systm.h>
        !            50:
        !            51: #include "stand.h"
        !            52: #include "net.h"
        !            53:
        !            54: /*
        !            55:  * Checksum routine for Internet Protocol family headers.
        !            56:  * This routine is very heavily used in the network
        !            57:  * code and should be modified for each CPU to be as fast as possible.
        !            58:  * In particular, it should not be this one.
        !            59:  */
        !            60: int
        !            61: in_cksum(void *p, int len)
        !            62: {
        !            63:        int sum = 0, oddbyte = 0, v = 0;
        !            64:        u_char *cp = p;
        !            65:
        !            66:        /* we assume < 2^16 bytes being summed */
        !            67:        while (len > 0) {
        !            68:                if (oddbyte) {
        !            69:                        sum += v + *cp++;
        !            70:                        len--;
        !            71:                }
        !            72:                if (((long)cp & 1) == 0) {
        !            73:                        while ((len -= 2) >= 0) {
        !            74:                                sum += *(u_short *)cp;
        !            75:                                cp += 2;
        !            76:                        }
        !            77:                } else {
        !            78:                        while ((len -= 2) >= 0) {
        !            79:                                sum += *cp++ << 8;
        !            80:                                sum += *cp++;
        !            81:                        }
        !            82:                }
        !            83:                if ((oddbyte = len & 1) != 0)
        !            84:                        v = *cp << 8;
        !            85:        }
        !            86:        if (oddbyte)
        !            87:                sum += v;
        !            88:        sum = (sum >> 16) + (sum & 0xffff); /* add in accumulated carries */
        !            89:        sum += sum >> 16;               /* add potential last carry */
        !            90:        return (0xffff & ~sum);
        !            91: }