Diff: main.cpp

Revision:

76:00e208cceb8b

Parent:

75:0d513869231f

Child:

77:abf92baebb42

--- a/main.cpp	Tue Jul 04 18:35:43 2017 +0000
+++ b/main.cpp	Wed Jul 05 20:05:42 2017 +0000
@@ -331,26 +331,28 @@
     }
 }
 
-unsigned int dataCheckSum(char * ptr, int len)
+unsigned int dataCheckSum(unsigned char * ptr, int len)
 {
+    
     unsigned int sum=0;
-    int placeHolder;
+    unsigned char placeHolder;
     if (len&1) {
-        placeHolder = ptr[len-1];    // when length is odd stuff in a zero byte
-        ptr[len-1]=0;
+        placeHolder = ptr[len];    // when length is odd stuff in a zero byte
+        ptr[len]=0;
     }
     for (int i=0; i<len/2; i++) {
-        int hi = *ptr;
+        unsigned int hi = *ptr;
         ptr++;
-        int lo = *ptr;
+        unsigned int lo = *ptr;
         ptr++;
-        int val = ( lo & 0xff ) | ( (hi<<8) & 0xff00 );
+        unsigned int val = ( (hi<<8) | lo );
         sum = sum + val;
     }
-    sum = sum + (sum>>16);
     if (len&1) {
-        ptr[len-1] = placeHolder;    // restore the last byte for odd lengths
+        ptr[len] = placeHolder;    // restore the last byte for odd lengths
     }
+    sum = (sum & 0xffff) + (sum>>16);
+    sum = (sum & 0xffff) + (sum>>16); // sum one more time to catch any carry from the carry
     return ~sum;
 }
 
@@ -409,9 +411,9 @@
         icmpSum[0]=0;
         icmpSum[1]=0; // zero the checksum for recalculation
         int icmpLength = packetLength - headerSizeIP; // length of ICMP data portion
-        int sum = dataCheckSum( icmpType, icmpLength); // this checksum on icmp data portion
-        icmpSum[0]=sum>>8;
-        icmpSum[1]=sum; // new checksum for ICMP data portion
+        unsigned int sum = dataCheckSum( (unsigned char *)icmpType, icmpLength); // this checksum on icmp data portion
+        icmpSum[0]=(sum>>8)&0xff;
+        icmpSum[1]=(sum   )&0xff; // new checksum for ICMP data portion
 
         int printSize = icmpLength-8; // exclude size of icmp header
         char * icmpData = icmpType+8; // the actual payload data is after the header
@@ -456,7 +458,7 @@
     char * flags =      ipPkt+6; // 2 bits
     char * ttl =        ipPkt+8; // 1 byte
     char * protocol =   ipPkt+9; // 1 byte
-    char * headercheck= ipPkt+10; // 2 bytes
+    unsigned char * headercheck= ipPkt+10; // 2 bytes
 #endif
     char * srcAdr =     ipPkt+12; // 4 bytes
     char * dstAdr =     ipPkt+16; // 4 bytes = total of 20 bytes
@@ -471,7 +473,7 @@
     int flagsIP = flags[0]>>14&3;
     int ttlIP = ttl[0];
     int protocolIP = protocol[0];
-    int checksumIP = (headercheck[0]<<8)|headercheck[1];
+    unsigned int checksumIP = (headercheck[0]<<8)|headercheck[1];
 #endif
 
     char srcIP [16];
@@ -697,7 +699,7 @@
 
     checksumtcp[0]=0;
     checksumtcp[1]=0;
-    unsigned int pseudoHeaderSum=dataCheckSum(pseudoHeader,tcpSize+12); // calculate the TCP checksum starting at the pseudo-header
+    unsigned int pseudoHeaderSum=dataCheckSum((unsigned char *)pseudoHeader,tcpSize+12); // calculate the TCP checksum starting at the pseudo-header
     checksumtcp[0]=pseudoHeaderSum>>8;
     checksumtcp[1]=pseudoHeaderSum;
     memcpy( s-12, tempHold, 12); // restore the 12 bytes that the pseudo-header overwrote