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Path: utzoo!watmath!watdaisy!ndiamond
From: ndiamond@watdaisy.UUCP (Norman Diamond)
Newsgroups: net.lang.c
Subject: Re: Un-alignment in structures
Message-ID: <7108@watdaisy.UUCP>
Date: Thu, 21-Mar-85 19:41:29 EST
Article-I.D.: watdaisy.7108
Posted: Thu Mar 21 19:41:29 1985
Date-Received: Fri, 22-Mar-85 01:25:16 EST
References: <9239@brl-tgr.ARPA>, <120@mit-athena.UUCP> <2821@ncsu.UUCP>
Organization: U of Waterloo, Ontario
Lines: 43

> When asking for unaligned structures in C, don't forget to ask that
> they be unaligned at the BIT level, because you might want to read
> tapes containing 36 or 60 bit words.

A 36-bit or 60-bit machine already has to make adjustments, regardless of
programming language or compiler or options.  9-track tapes, with 1 parity
bit, have 8-bit bytes written on them.  Similarly, networks are generally
specified to have 7-bit or 8-bit data, or 7-bit padded with a zero bit or
with parity.  The machine already must do some conversion.  Why make it
so much harder for a C programmer to complete the conversion?

> Also make sure that the compiler
> supports viewing numbers as having their bytes interchanged, because you
> might want to go from the VAX to something sane, occasionally.

If a machine's ports reverse the bytes from the protocol specified by the
network, then that machine's programs must make adjustments.  Again, why
should C make it harder?

Or if it's on tape, it is already known that data other than character
strings cannot really be regarded as portable.

> So we'll have to go
> with the next-best thing: a library of good, generic data-conversion routines.
> Fortunately, C provides lots of support for writing generic procedures.

But to overcome the padding, they will have to be in assembly or will have to
convert bytes (out of a char array) into ints.  For that matter, even the
char array doesn't work well on some machines; it may have to be assembly.

Yes I understand the earlier suggestion about a smiley face -- though the
submission wasn't just a joke, it was rhetoric with a certain message
intended.  I replied to the message.

-- 

   Norman Diamond

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"Opinions are those of the keyboard, and do not reflect on me or higher-ups."