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From: nick@sw.stratus.com (Nicolas Tamburri)
Newsgroups: comp.lang.forth
Subject: Re: Align
Message-ID: <6253@lectroid.sw.stratus.com>
Date: 21 Jun 91 17:36:22 GMT
References: <9106190432.AA02430@ucbvax.Berkeley.EDU> <6217@lectroid.sw.stratus.com> <1991Jun20.155046.4273@innovus.uucp>
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> rob@innovus.uucp (Rob Sciuk) writes:
>	The problem lies not with processors like the MC68000 family, 
>	which allow byte aligment (as do Intel) but the MC88000 and other 
>	RISC processors which REQUIRE word alignment (HP-PA, SPARC etc).

As far as I know, the 68000/6801x processors will fault if you try to execute a word mode instruction with a byte address.  However this "feature" was
corrected in the 68020 and after processor although with a penalty in access time, (which is probably what you were thinking of.)  I think my statement
stands: Necessary alignment is nothing new.

In any case:  I guess I see how your method works,  but I have a dissagreement
with it philosophically.  I don't mind CREATE aligning things behind my back,
if it is clearly documented that way.  I do mind ALLOT doing it however, since
this is a more general purpose word.  With your method, how do I create a
structure that looks like this:

[1 byte ( length )][15 bytes ( name )]

0 C, 15 ALLOT

without alloting an extra byte before the name?  What's the benefit of using C,
instead of , in this case?

I guess I would prefer to put the implict alignment inside words like "," "W,"
"L," etc, where it is obvious that if I use these to define a data structure, then
I will know enough to use the correct mode to access the data.  If I use ALLOT
however, I am implying that I want to access the data in unspecified, possibly
multiple ways.  If I do want the 15 bytes aligned,  I will align them manually,
which ensures my awareness that the bytes are not packed tightly.

In any case, the semantics are a matter of option.  We all do things our way.
My only problem with your method is if it restricts my ability to pack bytes.

							/nt

nick@kyron.sw.stratus.com