lib/libatm/ip_checksum.c

   1 /*
   2  *
   3  * ===================================
   4  * HARP  |  Host ATM Research Platform
   5  * ===================================
   6  *
   7  *
   8  * This Host ATM Research Platform ("HARP") file (the "Software") is
   9  * made available by Network Computing Services, Inc. ("NetworkCS")
  10  * "AS IS".  NetworkCS does not provide maintenance, improvements or
  11  * support of any kind.
  12  *
  13  * NETWORKCS MAKES NO WARRANTIES OR REPRESENTATIONS, EXPRESS OR IMPLIED,
  14  * INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF MERCHANTABILITY
  15  * AND FITNESS FOR A PARTICULAR PURPOSE, AS TO ANY ELEMENT OF THE
  16  * SOFTWARE OR ANY SUPPORT PROVIDED IN CONNECTION WITH THIS SOFTWARE.
  17  * In no event shall NetworkCS be responsible for any damages, including
  18  * but not limited to consequential damages, arising from or relating to
  19  * any use of the Software or related support.
  20  *
  21  * Copyright 1994-1998 Network Computing Services, Inc.
  22  *
  23  * Copies of this Software may be made, however, the above copyright
  24  * notice must be reproduced on all copies.
  25  *
  26  *      @(#) $FreeBSD: src/lib/libatm/ip_checksum.c,v 1.3.2.1 2001/09/28 16:52:10 dillon Exp $
  27  *      @(#) $DragonFly: src/lib/libatm/ip_checksum.c,v 1.4 2008/09/30 16:57:04 swildner Exp $
  28  *
  29  */
  30
  31 #include <sys/cdefs.h>
  32
  33 /*
  34  * User Space Library Functions
  35  * ----------------------------
  36  *
  37  * IP checksum computation
  38  *
  39  */
  40
  41 #include <sys/types.h>
  42 #include <sys/param.h>
  43 #include <sys/socket.h>
  44 #include <net/if.h>
  45 #include <netinet/in.h>
  46 #include <netatm/port.h>
  47 #include <netatm/atm.h>
  48 #include <netatm/atm_if.h>
  49 #include <netatm/atm_sap.h>
  50 #include <netatm/atm_sys.h>
  51 #include <netatm/atm_ioctl.h>
  52
  53 #include "libatm.h"
  54
  55 /*
  56  * Compute an IP checksum
  57  *
  58  * This code was taken from RFC 1071.
  59  *
  60  * "The following "C" code algorithm computes the checksum with an inner
  61  * loop that sums 16 bits at a time in a 32-bit accumulator."
  62  *
  63  * Arguments:
  64  *      addr    pointer to the buffer whose checksum is to be computed
  65  *      count   number of bytes to include in the checksum
  66  *
  67  * Returns:
  68  *      the computed checksum
  69  *
  70  */
  71 short
  72 ip_checksum(char *addr, int count)
  73 {
  74         /* Compute Internet Checksum for "count" bytes
  75          * beginning at location "addr".
  76          */
  77         long sum = 0;
  78
  79         while( count > 1 ) {
  80                 /* This is the inner loop */
  81                 sum += ntohs(* (unsigned short *) addr);
  82                 addr += sizeof(unsigned short);
  83                 count -= sizeof(unsigned short);
  84         }
  85
  86         /* Add left-over byte, if any */
  87         if( count > 0 )
  88                 sum += * (unsigned char *) addr;
  89
  90         /* Fold 32-bit sum to 16 bits */
  91         while (sum>>16)
  92                 sum = (sum & 0xffff) + (sum >> 16);
  93
  94         return((short)~sum);
  95 }