internetchecksum port problem

[cyclone atom]

Hello,

I'm porting the ping example from the winsock2 book to powerbasic. The problem I'm running in to is the InternetChecksum function. I know C++ a little, but I find this function difficult to convert to the powerbasic language. Maybe I could do it but I want to make sure that the function is correct, clean and fast .

The definition of the function is "the one's complement of the one's complement sum of all 16 bit words"

So if somebody could help me with this I will be very thankfull.

Ok this is the C function. I'm only intrested in the code that's inside the function. The parameters are : 1. A type 2. len of type (sizeof).

USHORT InternetChecksum(PUSHORT pBuf, int nLen)
{
int nSum = 0;

While(nlen > 0)
{
nSum += (*pBuf++);
nLen -= 2;
}

nSum = (nSum > 16) + (nSum & 0xffff);
nSum += (nsum > 16);
return(~nSum);
}

The checksum is a standard from RFC 791 IP.

Any help is appreciated even if it is a little.

Thanks



[This message has been edited by cyclone atom (edited March 05, 2000).]

[Scott Turchin]

Can't help you there, and I'm not sure how that works exactly, I had believed that was at a TCP/IP layer not an application layer, but I could be wrong..


However, I've already ported icmp_echo over, you can take my work and continue on if you like, it works but has some bugs in it....


Scott


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Scott
mailto:[email protected][email protected]</A>

[Erwin van de Wiel]

Hello,

I'm the same one who posted the first message and this is what I got. If somebody with C knowledge could verify it I would be very thankfull.

'USHORT InternetChecksum(PUSHORT pBuf, int nLen)
function InternetChecksum(header as word ptr, headerlen as long)as word
'{
'int nSum = 0;
dim nSum as long
nsum = 0

dim I as integer

while headerlen > 0
nsum = nsum + @header[i]
i = i + 1
headerlen = headerlen - 2
wend

'While(nlen > 0)
'{
'nSum += (*pBuf++);
'nLen -= 2;
'}

dim tempvar1 as long
dim tempvar2 as long
tempvar1 = nsum
shift right tempvar1,16
nsum = tempvar AND &hffff
tempvar2 = nsum
shift right tempvar2,16
nsum = nsum + tempvar2
InternetChecksum = NOT nsum
'nSum = (nSum > 16) + (nSum & 0xffff);
'nSum += (nsum > 16);
'return(~nSum);
'}

If someone could verify the conversion please.

Thanks

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[Raymond Penn]

This is code that I have working in my ping port which uses the low-level Winsock API.

I have it bolted into a program and it would take some time to pull it out into a usable example.

FUNCTION cksum(BYVAL buf AS DWORD, BYVAL blen AS LONG) AS WORD

DIM lsum AS DWORD
DIM bufp AS WORD PTR
DIM Intr???

bufp=buf

WHILE blen>0
[email protected]
INCR bufp
blen=blen-2
LOOP

intr???=lsum
SHIFT RIGHT intr???,16

lsum=(lsum + intr???)
SHIFT RIGHT intr???,16

lsum=(lsum + intr???) AND &h0FFFF

lsum=NOT lsum

FUNCTION=BITS??(lsum)
END FUNCTION


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[cyclone atom]

Well thank you both for the info.
I'm currently working some things out with the examples.

Raymond, I'm a little new at pbdll but why do you use the indicator for intr variable(???) and not a declaration as Dword ?

Another thing that I ran into is that in wsock32.inc the cksum from the icmp header is of type integer, while the cksum of an ip header type is a word (wich is the right one with the return value of the function)

I already send an email to support but I haven't got a reply yet.

Greetz
Erwin

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