Re: Dangerous UDP Checksum code ?!?

[Skybuck Flying]

Well anyway...

I think the idea can still work.

Assuming the maximum value for each word is: 65535.

And assuming a packet is maximum of 65535 words then multiple these two
should give the number of carries in the high word
correctly... so no overflows will occur... I checked that yesterday ! ;)

So to be on the safe side the code could be altered a little bit like so:

Carries := Sum shr 16;
Sum := Sum and $FFFF;
while Carries 0 do
begin
Sum := Sum + Carries;
Carries := Sum shr 16;
Sum := Sum and $FFFF;
end;

Or alternatively (probably shorter, less intuitive though):

Carries := 0;
repeat
Sum := Sum + Carries;
Carries := Sum shr 16;
Sum := Sum and $FFFF;
until Carries = 0;

Bye,
Skybuck.

[Skybuck Flying]

Re: Dangerous UDP Checksum code ?!?

Actually the maximum number of words in a packet is probably more close to
65535 div 2...

So that's about 32767 carries or so...in the maximum case...

So 32 bits more than enough to catch any possible carries ;)

Bye,
Skybuck.