From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: *
X-Spam-Status: No, score=1.5 required=5.0 tests=BAYES_00,FROMSPACE,
	FROM_ADDR_WS,INVALID_MSGID autolearn=no autolearn_force=no
	version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,a883dc07df0d6bb1,start
X-Google-Attributes: gid103376,public
From: " "@deneb.cygnus.argh.org (Florian Weimer)
Subject: Decoding an octet stream
Date: 1999/11/28
Message-ID: <877lj2q36g.fsf@deneb.cygnus.argh.org>#1/1
X-Deja-AN: 554045526
Mail-Copies-To: never
Content-Type: text/plain; charset=us-ascii
X-Complaints-To: abuse@cygnus.argh.org
X-Trace: deneb.cygnus.argh.org 943787623 8789 192.168.1.2 (28 Nov 1999
 11:13:43 GMT)
Organization: Penguin on board
Mime-Version: 1.0
User-Agent: Gnus/5.070099 (Pterodactyl Gnus v0.99) Emacs/20.4
NNTP-Posting-Date: 28 Nov 1999 11:13:43 GMT
Newsgroups: comp.lang.ada
Date: 1999-11-28T11:13:43+00:00
List-Id: <comp.lang.ada>

What is the best way to decode an octet stream (i.e. a sequence of
unsigned eight-bit values) with Ada?  The octet stream consists of
packet markes (single octets), two-octet integers (stored with the
most significant octet first), strings (sequences of octets of a given
length) and so on.  I don't want to use Ada.Sequential_IO, because it
would mean that only one octet can be read at a time, which seems to
be quite inefficient.

Streams seem to be nice, though.  If I specify the necessary
representation clauses, I think I'll only have to write a few 'Read
and 'Write operations, and composed types will be handled correctly
almost automatically.  But is this really portable?  Are there any
targets (except supercomputers, mainframes, and embedded systems)
where Stream_Element'Size isn't equal to 8?

BTW: I'm currently reading the two-octet integers using a construct like
`First_Octet * 2**8 + Second_Octet'.  Is it possible to denote the octet
ordering using a representation clause?  For a target with a matching
octet order, more efficient code could be generated.