On 21 Oct 2006 05:54:37 -0700, in bit.listserv.ibm-main
(Message-ID:<[EMAIL PROTECTED]>)
[EMAIL PROTECTED] (john gilmore) wrote:
Steve Comstock<[EMAIL PROTECTED]> writes:
Well, when you are learning Assembler, the work to write
reentrant (I, too, prefer that term to the relatively
new-fangled "reenterable") can get in the way of focusing
on simply how the instructions work and how to string
together series of instructions to accomplish specific tasks.
I still remember learning DOS assembler language well
over 20
years ago. I was taught about base and displacement addressing,
and told how to code the BALR and USING at the beginning of my
programs. What I most remember was, a week or so later, suddenly
*really* understanding what the BALR and USING did.
My experience was not unique. All of the students were
taught, "Put these statements at the beginnings of your programs
and eventually you'll understand what they do." Of course,
Base &
Displacement was taught and reiterated, but it takes time to sink
in.
(OS Assembler doesn't have this built-in AHA moment because
we are taught to get our addressability from R15.)
Until base and displacement addressing is fully
internalized,
you can't understand or appreciate RENT coding. Trying to teach
it before that simpler understanding is, IMO, counterproductive.
On the practical (as opposed to pedagogical) side: When I
write a utility program that reads, manipulates, and writes data,
I see no good reason to make it RENT. It's designed to be a
single program running as a batch step. What is the advantage of
copying DCBs and other control blocks into getmained storage?
That adds unneeded complexity to the code, which therefore makes
the program easier to miscode and harder to
maintain. ("Why write
it in Assembler?", you ask. Because it's one of my two best
languages.)
--
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