www.pudn.com > ids_snort.zip > checksum.c

/* $Id: checksum.c,v 1.2 2001/01/02 08:06:00 roesch Exp $ */ 
/* 
** Copyright (C) 1998,1999,2000,2001 Martin Roesch  
** 
** 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. 
** 
** This program is distributed in the hope that it will be useful, 
** but WITHOUT ANY WARRANTY; without even the implied warranty of 
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
** GNU General Public License for more details. 
** 
** You should have received a copy of the GNU General Public License 
** along with this program; if not, write to the Free Software 
** Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. 
*/ 
 
#include "checksum.h" 
 
/* 
 * Function: checksum(u_int16_t *, u_int32_t, u_int16_t *, u_int32_t) 
 * 
 * Purpose: Huh huh, math.... 
 * 
 * Arguments: b1   => pointer to data set one 
 *            len1 => length of data set one 
 *            b2   => pointer to data set two 
 *            len2 => length of data set two 
 * 
 * Returns: csum => the calculated checksum for the given data 
 */ 
u_int16_t checksum(u_int16_t *b1, u_int32_t len1, u_int16_t *b2, u_int32_t len2) 
{ 
    u_int32_t sum = 0; 
 
    if(b1 != (u_int16_t *)NULL)  
    { 
        while(len1 > 1)  
        { 
            sum += *((u_int16_t *)b1 ++); 
 
            if(sum & 0x80000000) 
            { 
                sum = (sum & 0xffff) + (sum >> 16); 
            } 
 
            len1 -= 2; 
        } 
     
        /* we'll have problems if b2 exists and len1 is odd */ 
        if(len1) 
        { 
           sum += (u_int16_t) * (u_int8_t*) b1; 
        } 
    } 
 
    if(b2 != (u_int16_t*)NULL)  
    { 
        while(len2 > 1)  
        { 
            sum += *((u_int16_t*)b2 ++); 
 
            if(sum & 0x80000000) 
            { 
                sum = (sum & 0xffff) + (sum >> 16); 
            } 
 
            len2 -= 2; 
        } 
 
        if(len2) 
        { 
            sum += (u_int16_t) * (u_int8_t*) b2; 
        } 
    } 
 
    while(sum >> 16) 
        sum = (sum & 0xffff) + (sum >> 16); 
 
    return ~sum; 
}