Logo Search packages:      
Sourcecode: linux-2.6 version File versions

checksum.c

/*
 * arch/alpha/lib/checksum.c
 *
 * This file contains network checksum routines that are better done
 * in an architecture-specific manner due to speed..
 * Comments in other versions indicate that the algorithms are from RFC1071
 *
 * accellerated versions (and 21264 assembly versions ) contributed by
 *    Rick Gorton <rick.gorton@alpha-processor.com>
 */
 
#include <linux/module.h>
#include <linux/string.h>

#include <asm/byteorder.h>

static inline unsigned short from64to16(unsigned long x)
{
      /* Using extract instructions is a bit more efficient
         than the original shift/bitmask version.  */

      union {
            unsigned long     ul;
            unsigned int      ui[2];
            unsigned short    us[4];
      } in_v, tmp_v, out_v;

      in_v.ul = x;
      tmp_v.ul = (unsigned long) in_v.ui[0] + (unsigned long) in_v.ui[1];

      /* Since the bits of tmp_v.sh[3] are going to always be zero,
         we don't have to bother to add that in.  */
      out_v.ul = (unsigned long) tmp_v.us[0] + (unsigned long) tmp_v.us[1]
                  + (unsigned long) tmp_v.us[2];

      /* Similarly, out_v.us[2] is always zero for the final add.  */
      return out_v.us[0] + out_v.us[1];
}

/*
 * computes the checksum of the TCP/UDP pseudo-header
 * returns a 16-bit checksum, already complemented.
 */
unsigned short int csum_tcpudp_magic(unsigned long saddr,
                           unsigned long daddr,
                           unsigned short len,
                           unsigned short proto,
                           unsigned int sum)
{
      return ~from64to16(saddr + daddr + sum +
            ((unsigned long) ntohs(len) << 16) +
            ((unsigned long) proto << 8));
}

unsigned int csum_tcpudp_nofold(unsigned long saddr,
                           unsigned long daddr,
                           unsigned short len,
                           unsigned short proto,
                           unsigned int sum)
{
      unsigned long result;

      result = (saddr + daddr + sum +
              ((unsigned long) ntohs(len) << 16) +
              ((unsigned long) proto << 8));

      /* Fold down to 32-bits so we don't lose in the typedef-less 
         network stack.  */
      /* 64 to 33 */
      result = (result & 0xffffffff) + (result >> 32);
      /* 33 to 32 */
      result = (result & 0xffffffff) + (result >> 32);
      return result;
}

/*
 * Do a 64-bit checksum on an arbitrary memory area..
 *
 * This isn't a great routine, but it's not _horrible_ either. The
 * inner loop could be unrolled a bit further, and there are better
 * ways to do the carry, but this is reasonable.
 */
static inline 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 << 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;
}

/*
 *    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 long result = do_csum(buff, len);

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

EXPORT_SYMBOL(csum_partial);

/*
 * this routine is used for miscellaneous IP-like checksums, mainly
 * in icmp.c
 */
unsigned short ip_compute_csum(unsigned char * buff, int len)
{
      return ~from64to16(do_csum(buff,len));
}

Generated by  Doxygen 1.6.0   Back to index