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/* SCTP kernel reference Implementation

 * Copyright (c) 1999-2000 Cisco, Inc.

 * Copyright (c) 1999-2001 Motorola, Inc.

 * Copyright (c) 2003 International Business Machines, Corp.

 *

 * This file is part of the SCTP kernel reference Implementation

 *

 * This file has direct heritage from the SCTP user-level reference

 * implementation by R. Stewart, et al.  These functions implement the

 * Adler-32 algorithm as specified by RFC 2960.

 *

 * The SCTP reference implementation is free software;

 * you can redistribute it and/or modify it under the terms of

 * the GNU General Public License as published by

 * the Free Software Foundation; either version 2, or (at your option)

 * any later version.

 *

 * The SCTP reference implementation is distributed in the hope that it

 * will be useful, but WITHOUT ANY WARRANTY; without even the implied

 *                 ************************

 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

 * See the GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with GNU CC; see the file COPYING.  If not, write to

 * the Free Software Foundation, 59 Temple Place - Suite 330,

 * Boston, MA 02111-1307, USA.

 *

 * Please send any bug reports or fixes you make to the

 * email address(es):

 *    lksctp developers <lksctp-developers@lists.sourceforge.net>

 *

 * Or submit a bug report through the following website:

 *    http://www.sf.net/projects/lksctp

 *

 * Written or modified by:

 *    Randall Stewart <rstewar1@email.mot.com>

 *    Ken Morneau     <kmorneau@cisco.com>

 *    Qiaobing Xie    <qxie1@email.mot.com>

 *    Sridhar Samudrala <sri@us.ibm.com>

 *

 * Any bugs reported given to us we will try to fix... any fixes shared will

 * be incorporated into the next SCTP release.

 */

/* This is an entry point for external calls

 * Define this function in the header file. This is

 * direct from rfc1950, ...

 *

 * The following C code computes the Adler-32 checksum of a data buffer.

 * It is written for clarity, not for speed.  The sample code is in the

 * ANSI C programming language. Non C users may find it easier to read

 * with these hints:

 *

 *    &      Bitwise AND operator.

 *    >>     Bitwise right shift operator. When applied to an

 *           unsigned quantity, as here, right shift inserts zero bit(s)

 *           at the left.

 *    <<     Bitwise left shift operator. Left shift inserts zero

 *           bit(s) at the right.

 *    ++     "n++" increments the variable n.

 *    %      modulo operator: a % b is the remainder of a divided by b.

 *

 * Well, the above is a bit of a lie, I have optimized this a small

 * tad, but I have commented the original lines below

 */

#include <linux/types.h>

#include <net/sctp/sctp.h>

#define BASE 65521 /* largest prime smaller than 65536 */

/* Performance work as shown this pig to be the

 * worst CPU wise guy. I have done what I could think

 * of on my flight to Australia but I am sure some

 * clever assembly could speed this up, but of

 * course this would require the dreaded #ifdef's for

 * architecture. If you can speed this up more, pass

 * it back and we will incorporate it :-)

 */

unsigned long update_adler32(unsigned long adler,

                             unsigned char *buf, int len)

{

        __u32 s1 = adler & 0xffff;

        __u32 s2 = (adler >> 16) & 0xffff;

        int n;

        for (n = 0; n < len; n++,buf++) {

                /* s1 = (s1 + buf[n]) % BASE */

                /* first we add */

                s1 = (s1 + *buf);

                /* Now if we need to, we do a mod by

                 * subtracting. It seems a bit faster

                 * since I really will only ever do

                 * one subtract at the MOST, since buf[n]

                 * is a max of 255.

                 */

                if (s1 >= BASE)

                        s1 -= BASE;

                /* s2 = (s2 + s1) % BASE */

                /* first we add */

                s2 = (s2 + s1);

                /* again, it is more efficient (it seems) to

                 * subtract since the most s2 will ever be

                 * is (BASE-1 + BASE-1) in the worse case.

                 * This would then be (2 * BASE) - 2, which

                 * will still only do one subtract. On Intel

                 * this is much better to do this way and

                 * avoid the divide. Have not -pg'd on

                 * sparc.

                 */

                if (s2 >= BASE) {

                        /*      s2 %= BASE;*/

                        s2 -= BASE;

                }

        }

        /* Return the adler32 of the bytes buf[0..len-1] */

        return (s2 << 16) + s1;

}

__u32 sctp_start_cksum(__u8 *ptr, __u16 count)

{

        /*

         * Update a running Adler-32 checksum with the bytes

         * buf[0..len-1] and return the updated checksum. The Adler-32

         * checksum should be initialized to 1.

         */

        __u32 adler = 1L;

        __u32 zero = 0L;

        /* Calculate the CRC up to the checksum field. */

        adler = update_adler32(adler, ptr,

                               sizeof(struct sctphdr) - sizeof(__u32));

        /* Skip over the checksum field. */

        adler = update_adler32(adler, (unsigned char *) &zero,

                               sizeof(__u32));

        ptr += sizeof(struct sctphdr);

        count -= sizeof(struct sctphdr);

        /* Calculate the rest of the Adler-32. */

        adler = update_adler32(adler, ptr, count);

        return adler;

}

__u32 sctp_update_cksum(__u8 *ptr, __u16 count, __u32 adler)

{

        adler = update_adler32(adler, ptr, count);

        return adler;

}

__u32 sctp_update_copy_cksum(__u8 *to, __u8 *from, __u16 count, __u32 adler)

{

        /* Its not worth it to try harder.  Adler32 is obsolescent. */

        adler = update_adler32(adler, from, count);

        memcpy(to, from, count);

        return adler;

}

__u32 sctp_end_cksum(__u32 adler)

{

        return adler;

}