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checksum.c

/*
 * Copyright 2004-2009 Analog Devices Inc.
 *
 * Licensed under the GPL-2 or later.
 *
 * An implementation of the TCP/IP protocol suite for the LINUX operating
 * system. INET is implemented using the BSD Socket interface as the
 * means of communication with the user level.
 *
 */

#include <linux/module.h>
#include <net/checksum.h>
#include <asm/checksum.h>

#ifdef CONFIG_IP_CHECKSUM_L1
static unsigned short do_csum(const unsigned char *buff, int len)__attribute__((l1_text));
#endif

static unsigned short do_csum(const unsigned char *buff, int len)
{
      register unsigned long sum = 0;
      int swappem = 0;

      if (1 & (unsigned long)buff) {
            sum = *buff << 8;
            buff++;
            len--;
            ++swappem;
      }

      while (len > 1) {
            sum += *(unsigned short *)buff;
            buff += 2;
            len -= 2;
      }

      if (len > 0)
            sum += *buff;

      /*  Fold 32-bit sum to 16 bits */
      while (sum >> 16)
            sum = (sum & 0xffff) + (sum >> 16);

      if (swappem)
            sum = ((sum & 0xff00) >> 8) + ((sum & 0x00ff) << 8);

      return sum;

}

/*
 *    This is a version of ip_compute_csum() optimized for IP headers,
 *    which always checksum on 4 octet boundaries.
 */
__sum16 ip_fast_csum(unsigned char *iph, unsigned int ihl)
{
      return (__force __sum16)~do_csum(iph, ihl * 4);
}
EXPORT_SYMBOL(ip_fast_csum);

/*
 * 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
 */
__wsum csum_partial(const void *buff, int len, __wsum sum)
{
      /*
       * Just in case we get nasty checksum data...
       * Like 0xffff6ec3 in the case of our IPv6 multicast header.
       * We fold to begin with, as well as at the end.
       */
      sum = (sum & 0xffff) + (sum >> 16);

      sum += do_csum(buff, len);

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

      return sum;
}
EXPORT_SYMBOL(csum_partial);

/*
 * this routine is used for miscellaneous IP-like checksums, mainly
 * in icmp.c
 */
__sum16 ip_compute_csum(const void *buff, int len)
{
      return (__force __sum16)~do_csum(buff, len);
}
EXPORT_SYMBOL(ip_compute_csum);

/*
 * copy from fs while checksumming, otherwise like csum_partial
 */

__wsum
csum_partial_copy_from_user(const void __user *src, void *dst,
                      int len, __wsum sum, int *csum_err)
{
      if (csum_err)
            *csum_err = 0;
      memcpy(dst, (__force void *)src, len);
      return csum_partial(dst, len, sum);
}
EXPORT_SYMBOL(csum_partial_copy_from_user);

/*
 * copy from ds while checksumming, otherwise like csum_partial
 */

__wsum csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
{
      memcpy(dst, src, len);
      return csum_partial(dst, len, sum);
}
EXPORT_SYMBOL(csum_partial_copy);

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