Rollover Issue

[raj]

Hi,

I am dealing with the sequence number rollover issue.
I need to compare the incoming packet sequence number w/ the one in the
table. There is good possibility that the incoming packet sequence number
has rolledover. I am using Unsigned data type to store the sequence number.
I read somewhere that I 've to do Signed arithmetic to deal with it.

I would appreciate if you can help me out. (Pseudo code would be helpful)

Thanks.

 

[Nick Austin]

Hi,

I am dealing with the sequence number rollover issue.
I need to compare the incoming packet sequence number w/ the one in the
table. There is good possibility that the incoming packet sequence number
has rolledover. I am using Unsigned data type to store the sequence number.
I read somewhere that I 've to do Signed arithmetic to deal with it.

You mean something like this:

#define N 64

unsigned long difference( unsigned long seq1, unsigned long seq2 )
{
return ( seq2 + N - seq1 ) % N;
}

Nick.