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checksum.c

/*
 * INET           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.
 *
 *          MIPS specific IP/TCP/UDP checksumming routines
 *
 * Authors: Ralf Baechle, <ralf@waldorf-gmbh.de>
 *          Lots of code moved from tcp.c and ip.c; see those files
 *          for more names.
 *
 *          This program 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 of the License, or (at your option) any later version.
 *
 * $Id: checksum.c,v 1.1 2002/09/28 14:58:40 gerg Exp $
 */
#include <net/checksum.h>
#include <linux/module.h>
#include <linux/types.h>
#include <asm/byteorder.h>
#include <asm/string.h>
#include <asm/uaccess.h>

static inline unsigned short from32to16 (unsigned long sum)
{
      unsigned int result;
      /*
                          %0        %1
            hsw %1, %0  H     L           L     H
            add %1, %0  H     L           H+L+C H+L
      */
      asm ("hsw %1, %0; add %1, %0" : "=&r" (result) : "r" (sum));
      return result >> 16;
}

static inline unsigned int do_csum(const unsigned char * buff, int len)
{
      int odd, count;
      unsigned int result = 0;

      if (len <= 0)
            goto out;
      odd = 1 & (unsigned long) buff;
      if (odd) {
            result = be16_to_cpu(*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) {
                  unsigned int carry = 0;
                  do {
                        unsigned int w = *(unsigned int *) buff;
                        count--;
                        buff += 4;
                        result += carry;
                        result += w;
                        carry = (w > result);
                  } while (count);
                  result += carry;
                  result = (result & 0xffff) + (result >> 16);
            }
            if (len & 2) {
                  result += *(unsigned short *) buff;
                  buff += 2;
            }
      }
      if (len & 1)
            result += le16_to_cpu(*buff);
      result = from32to16(result);
      if (odd)
            result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
out:
      return result;
}

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

/*
 * 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);
}

/*
 * computes a partial checksum, e.g. for TCP/UDP fragments
 */
__wsum csum_partial(const void *buff, int len, __wsum sum)
{
      unsigned int result = do_csum(buff, len);

      /* add in old sum, and carry.. */
      result += (__force u32)sum;
      if ((__force u32)sum > result)
            result += 1;
      return (__force __wsum)result;
}

EXPORT_SYMBOL(csum_partial);

/*
 * copy while checksumming, otherwise like csum_partial
 */
__wsum csum_partial_copy_nocheck(const void *src, void *dst,
                               int len, __wsum sum)
{
      /*
       * It's 2:30 am and I don't feel like doing it real ...
       * This is lots slower than the real thing (tm)
       */
      sum = csum_partial(src, len, sum);
      memcpy(dst, src, len);

      return sum;
}

/*
 * Copy from userspace and compute checksum.  If we catch an exception
 * then zero the rest of the buffer.
 */
__wsum csum_partial_copy_from_user (const void *src,
                                void *dst,
                                          int len, __wsum sum,
                                          int *err_ptr)
{
      int missing;

      missing = copy_from_user(dst, src, len);
      if (missing) {
            memset(dst + len - missing, 0, missing);
            *err_ptr = -EFAULT;
      }
            
      return csum_partial(dst, len, sum);
}

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