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/*

 * INET         An implementation of the TCP/IP protocol suite for the LINUX

 *              operating system.

 *

 *              IP/TCP/UDP checksumming routines

 *

 * Authors:     Keith Adams,    <kma@cse.ogi.edu>

 *              Jorge Cwik, <jorge@laser.satlink.net>

 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>

 *              Tom May, <ftom@netcom.com>

 *              Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>

 *              Lots of code moved from tcp.c and ip.c; see those files

 *              for more names.

 *

 */

#include <net/checksum.h>

#if 1

static unsigned long do_csum(const unsigned char * buff, int len)

{

        int odd, count;

        unsigned long result = 0;

        if (len <= 0)

                goto out;

        odd = 1 & (unsigned long) buff;

        if (odd) {

                result = *buff;

                len--;

                buff++;

        }

        count = len >> 1;               /* nr of 16-bit words.. */

        if (count) {

                if (2 & (unsigned long) buff) {

                        result += *(unsigned short *) buff;

                        count--;

                        len -= 2;

                        buff += 2;

                }

                count >>= 1;            /* nr of 32-bit words.. */

                if (count) {

#if 1

                        unsigned long carry = 0;

                        do {

                                unsigned long w = *(unsigned long *) buff;

                                count--;

                                buff += 4;

                                result += carry;

                                result += w;

                                carry = (w > result);

                        } while (count);

                        result += carry;

#else

                        asm("cmpo       0, 1");         /* clear carry */

                        do {

                                unsigned long w = *(unsigned long*) buff;

                                count--;

                                buff += 4;

                                asm("addc       0, %0, %0\n\t"  /* r += carry */

                                    "cmpo       0, 1\n\t"       /* reset c */

                                    "addc       %1, %0, %0"     /* r += w */

                                    : "=&r"(result)

                                    : "r"(w), "0"(result));

                        } while (count);

                        asm("addc       0, %0, %0"      /* result += carry */

                            : "=r"(result) : "0"(result));

#endif

                        result = (result & 0xffff) + (result >> 16);

                }

                if (len & 2) {

                        result += *(unsigned short *) buff;

                        buff += 2;

                }

        }

        if (len & 1)

                result += *buff;

        result = from32to16(result);

        if (odd)

                return ntohs(result);

out:

        return result;

}

#else

/*

 * Naive implementation stolen from Stevens

 */

static unsigned long do_csum(const unsigned char * buff, int len)

{

        long sum=0;

        while (len > 1) {

                sum += *((unsigned short*)buff)++;

                if (sum & (1<<31))

                        sum = (sum & 0xffff);

                len -= 2;

        }

        if (len)

                sum += (unsigned short) *buff;

        while (sum >> 16)

                sum = (sum & 0xffff) + (sum >> 16);

        return sum;

}

#endif

/*

 *      This is a version of ip_compute_csum() optimized for IP headers,

 *      which always checksum on 4 octet boundaries.

 */

unsigned short ip_fast_csum(unsigned char * iph, unsigned int ihl)

{

        return ~do_csum(iph,ihl*4);

}

/*

 * computes the checksum of a memory block at buff, length len,

 * and adds in "sum" (32-bit)

 *

 * returns a 32-bit number suitable for feeding into itself

 * or csum_tcpudp_magic

 *

 * this function must be called with even lengths, except

 * for the last fragment, which may be odd

 *

 * it's best to have buff aligned on a 32-bit boundary

 */

unsigned int csum_partial(const unsigned char * buff, int len, unsigned int sum)

{

        unsigned int result = do_csum(buff, len);

        /* add in old sum, and carry.. */

        result += sum;

        /* 16+c bits -> 16 bits */

        result = (result & 0xffff) + (result >> 16);

        return result;

}

/*

 * this routine is used for miscellaneous IP-like checksums, mainly

 * in icmp.c

 */

unsigned short ip_compute_csum(const unsigned char * buff, int len)

{

        return ~do_csum(buff,len);

}

/*

 * copy from fs while checksumming, otherwise like csum_partial

 */

unsigned int

csum_partial_copy_fromuser(const char *src, char *dst, int len, int sum)

{

        memcpy(dst, src, len);

        return csum_partial(dst, len, sum);

}

/*

 * copy from ds while checksumming, otherwise like csum_partial

 */

unsigned int

csum_partial_copy(const char *src, char *dst, int len, int sum)

{

        memcpy(dst, src, len);

        return csum_partial(dst, len, sum);

}