# zero length segments!

Chandrashekhar Mullaparthi Chandrashekhar.Mullaparthi@REDACTED
Tue Sep 24 16:35:14 CEST 2002

```I've had the same problem. You have to do

Var = 31 - Bit,
<<_:Var, Flag:1, _:(Bit)>> = <<1:32>>,

cheers
Chandru

-----Original Message-----
From: Vance Shipley [mailto:vances@REDACTED]
Sent: 24 September 2002 15:03
To: erlang-questions@REDACTED
Subject: Re: zero length segments!

Well didn't I speak too soon!  While this works wonderfully in the shell
it won't complile. :(

Eshell V5.1.2  (abort with ^G)
1> T = fun(Bit) -> <<_:(31 - Bit), Flag:1, _:(Bit)>> = <<1:32>>, Flag end.
#Fun<erl_eval.5.63972567>
2> T(0).
1
3> T(1).
0

-module(t).
-export([t/1]).

t(Bit) when integer(Bit) ->
<<_:(31 - Bit), Flag:1, _:(Bit)>> = <<1:32>>,
Flag.

1> c(t).
./t.erl:5: illegal bit size
error

The problem seems to be with the expression (31 - Bit).

Any idea how to get past this?

-Vance

Vance Shipley
Motivity Telecom Inc.
+1 519 579 5816
vances@REDACTED

On Tue, Sep 24, 2002 at 06:33:23AM -0400, Vance Shipley wrote:
>
> Was I ever happily suprised when I found that this was a valid expression:
>
> 	<<0:8, 1:24, 0:0>>
>
> It results in:
>
> 	<<0,0,0,1>>
>
> The reason this is so good is that it I don't have to handle a special
> case when X=0:
>
> 	Flag = <<_:(31-X), Flag:1, _:(X)>>
>
> Of course I'm sure that that is why it works, I'm just very happy about
it. :)
>
> 	-Vance

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