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From: wv12@my-deja.com
Subject: Re: First time Ada has let me down
Date: 2000/10/25
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References: <8FD7DEBEEsynoptikdamudderfuck@news>
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In article <8FD7DEBEEsynoptikdamudderfuck@news>,
  avlogue@home.com (Shifty) wrote:
> OK, here's the story:
>
> I had a problem at work where I needed to calculate the offset of a
> "magic number" within a buffer containing an IP datagram.
>
> The magic number is 3 protocol headers deep within the datagram, and
> all three headers are variable length.  I needed to find the HLEN
> fields of the IP and TCP headers in memory.  Turns out both of these
> are stored in 4 bits.  The data in the other 4 bits of the octet
> belong to another field in the header.
>
the IP header length occupies the 4 LSB. Assuming p pointing to the
byte offset,
the length is just len = (*p)&0xf;
the TCP header length occupies the 4 MSB. the length in this case
is then  ((*p)&0xf0)>>4;
Things just have to be easy in C, don't they. No wonder 99.99% of the
IP stacks in the world are in C and not Ada.


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