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csum_partial_copy.c

/*
 * Network Checksum & Copy routine
 *
 * Copyright (C) 1999, 2003-2004 Hewlett-Packard Co
 *    Stephane Eranian <eranian@hpl.hp.com>
 *
 * Most of the code has been imported from Linux/Alpha
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/string.h>

#include <asm/uaccess.h>

/*
 * XXX Fixme: those 2 inlines are meant for debugging and will go away
 */
static inline unsigned
short from64to16(unsigned long x)
{
      /* add up 32-bit words for 33 bits */
      x = (x & 0xffffffff) + (x >> 32);
      /* add up 16-bit and 17-bit words for 17+c bits */
      x = (x & 0xffff) + (x >> 16);
      /* add up 16-bit and 2-bit for 16+c bit */
      x = (x & 0xffff) + (x >> 16);
      /* add up carry.. */
      x = (x & 0xffff) + (x >> 16);
      return x;
}

static inline
unsigned long do_csum_c(const unsigned char * buff, int len, unsigned int psum)
{
      int odd, count;
      unsigned long result = (unsigned long)psum;

      if (len <= 0)
            goto out;
      odd = 1 & (unsigned long) buff;
      if (odd) {
            result = *buff << 8;
            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 (4 & (unsigned long) buff) {
                        result += *(unsigned int *) buff;
                        count--;
                        len -= 4;
                        buff += 4;
                  }
                  count >>= 1;      /* nr of 64-bit words.. */
                  if (count) {
                        unsigned long carry = 0;
                        do {
                              unsigned long w = *(unsigned long *) buff;
                              count--;
                              buff += 8;
                              result += carry;
                              result += w;
                              carry = (w > result);
                        } while (count);
                        result += carry;
                        result = (result & 0xffffffff) + (result >> 32);
                  }
                  if (len & 4) {
                        result += *(unsigned int *) buff;
                        buff += 4;
                  }
            }
            if (len & 2) {
                  result += *(unsigned short *) buff;
                  buff += 2;
            }
      }
      if (len & 1)
            result += *buff;

      result = from64to16(result);

      if (odd)
            result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);

out:
      return result;
}

/*
 * XXX Fixme
 *
 * This is very ugly but temporary. THIS NEEDS SERIOUS ENHANCEMENTS.
 * But it's very tricky to get right even in C.
 */
extern unsigned long do_csum(const unsigned char *, long);

__wsum
csum_partial_copy_from_user(const void __user *src, void *dst,
                        int len, __wsum psum, int *errp)
{
      unsigned long result;

      /* XXX Fixme
       * for now we separate the copy from checksum for obvious
       * alignment difficulties. Look at the Alpha code and you'll be
       * scared.
       */

      if (__copy_from_user(dst, src, len) != 0 && errp)
            *errp = -EFAULT;

      result = do_csum(dst, len);

      /* add in old sum, and carry.. */
      result += (__force u32)psum;
      /* 32+c bits -> 32 bits */
      result = (result & 0xffffffff) + (result >> 32);
      return (__force __wsum)result;
}

EXPORT_SYMBOL(csum_partial_copy_from_user);

__wsum
csum_partial_copy_nocheck(const void *src, void *dst, int len, __wsum sum)
{
      return csum_partial_copy_from_user((__force const void __user *)src,
                                 dst, len, sum, NULL);
}

EXPORT_SYMBOL(csum_partial_copy_nocheck);

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