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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 1.3 1997/12/01 17:57:34 ralf Exp $
 */
#include <linux/module.h>
#include <linux/types.h>

#include <net/checksum.h>
#include <asm/byteorder.h>
#include <asm/string.h>
#include <asm/uaccess.h>

#define addc(_t,_r)                     \
      __asm__ __volatile__ (          \
"       add             %0, %1, %0\n"   \
"       addc            %0, %%r0, %0\n" \
      : "=r"(_t)                      \
      : "r"(_r), "0"(_t));

static inline unsigned short from32to16(unsigned int x)
{
      /* 32 bits --> 16 bits + carry */
      x = (x & 0xffff) + (x >> 16);
      /* 16 bits + carry --> 16 bits including carry */
      x = (x & 0xffff) + (x >> 16);
      return (unsigned short)x;
}

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) {
                  while (count >= 4) {
                        unsigned int r1, r2, r3, r4;
                        r1 = *(unsigned int *)(buff + 0);
                        r2 = *(unsigned int *)(buff + 4);
                        r3 = *(unsigned int *)(buff + 8);
                        r4 = *(unsigned int *)(buff + 12);
                        addc(result, r1);
                        addc(result, r2);
                        addc(result, r3);
                        addc(result, r4);
                        count -= 4;
                        buff += 16;
                  }
                  while (count) {
                        unsigned int w = *(unsigned int *) buff;
                        count--;
                        buff += 4;
                        addc(result, w);
                  }
                  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 = swab16(result);
out:
      return result;
}

/*
 * computes a partial checksum, e.g. for TCP/UDP fragments
 */
/*
 * why bother folding?
 */
__wsum csum_partial(const void *buff, int len, __wsum sum)
{
      unsigned int result = do_csum(buff, len);
      addc(result, sum);
      return (__force __wsum)from32to16(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;
}
EXPORT_SYMBOL(csum_partial_copy_nocheck);

/*
 * 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 __user *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);
}
EXPORT_SYMBOL(csum_partial_copy_from_user);

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