Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!ames!umd5!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.arch
Subject: Re: using assembler (vs HLL, etc)
Message-ID: <12729@mimsy.UUCP>
Date: 29 Jul 88 02:26:11 GMT
References: <1086@garth.UUCP> <76700041@p.cs.uiuc.edu>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 49

In article <76700041@p.cs.uiuc.edu> gillies@p.cs.uiuc.edu writes:
>I have a hard time believing people who claim that assembly is more
>modifiable than a high level language.

I think they mean that the assemblER (the thing that reads the program
source and generates the program object) is more flexible/modifiable
than a higher-level language compiler.  This I find easy to believe.

Before I had decent HLL compilers available to me (when I was
programming on a TRS-80 model I with bits of homebrew hardware and
software: now *that* is primitive :-) ) I did some fairly extensive
Z80 assembly programming.  The only way I could keep track of what I
was doing was to stick to a particular discipline.  Within that, I
was at least as restricted as by a compiler.

Given that (voluntary) set of restrictions, none of the following
were particularly difficult:

>(c) Extensively revising a struct {} data type to add and remove
>fields, then recompiling.

(Done by using various label conventions.  It would have been nice had
I had something to do this for me.)

>(d) increasing the local storage of a subroutine from 5 words (smaller
>than the register set) to 50 words (probably larger than the register
>set).

(Use the stack.  Painful; stack-relative references are *hard* on a Z80.
The typical trick is to use IX or IY; this is slow.)

>(e) Changing a subroutine interface specification (adding & removing
>arguments) & making sure all the calls are updated appropriately.

(A matter of checking all the calls.  Typically pointers were in HL and
integers in BC, or [if small] in B, C, or A.  If many arguments, some
went on the stack, or in a `structure' with a descriptor in HL.)

>With a high level language (C/Modula-II), these changes are instant
>and trivial.

Not all of them, perhaps, but the point is that the HLL helps me to do
this: it makes it much easier, and that is why I use(d) it.  (The
TRS-80 has been off for years, now; it has a bad 4116 somewhere in the
expansion interface, and I have not the inclination to hunt it down,
nor do I have any idea where, or even whether, these 16K chips are
still available.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris