Bit syntax frustrations, again
Thu Oct 3 20:39:31 CEST 2002
Vance Shipley wrote:
>I am working heavily with the bit syntax right now and my two cents
>on this matter is that it is unfortunate that I can't do this:
> <<Header:32, Payload/binary, Trailer:16>> = Packet
>It would make my life a lot easier.
You need to give the emulator some hint on the length of Payload,
we had two different ways in the prototype.
1. The header contains the length of PayLoad
<<Len:16, Header:16, Payload:Len/binary, Trailer:16>> = Packet
In this case we used Variable bindings from left to right which was
a bit controversial... (I do not remember why :-) The first
Len can be used later on in the bit pattern.
2. The pattern search.
Assume that Trailer is bound then the pattern
<<Header:32, Payload/binary, Trailer:16>> = Packet
Would be interpreted as "first get the header" then start search
for a bit pattern "Trailer" when "Trailer" is found then bind the
Payload to the bits(bytes).
Something like that?
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