Section 2 - Commodore Computers

tvk:rv. 1Q82.lssue 24 COMPUTEI 153
Moy. 1982. Issue 24 COMPUTE! 153
"Garbage collection" reJers 10 the Long deLa.ys which can
"Garbage collection" refers to the long delays which can
occur while whiLe the computer cOllllmler rearranges strings. slrings. This is article (".tieLe
shows how to 10 avoid these lhesf delays dela)'.' when you are a.re working
riling
with significant numbers of strings. The Th.e technique "~clmiq/l (J here h(lre
is most lIIosllIseJll1 useful for J01' PET/CBM owners who have alder older
machines. lIIachines. Newer machines with wilh BASIC 4.0 avoid these Ih ese
problems. Inob/ellls.
Screen Input
Screen Input
On The PET
On The PET
Elizabeth Deal
Elizabeth Dea
Malvern, PA
Usin g the information placed on the screen as a
Using the information placed on the screen as a
source ofo f input inpul seems like a contradiction contradicLion in terms.
Why should one bother inputting something when
' Nh y should one bothe r inputtin g somethi ng when
one alread y knows what it is' I stumbled upon one
one already knows what it is? I stumbled upon one
good reason and worked with it to a happy py ending:
no garbage collecti on delays.
no garbage collection delays.
ThisT article runs through a series ofo f small
experimments. Both BOlh tests and conclusions are based
on work in the Upgrade PET. Users of ori gi nal
on work in the Upgrade PET. Users of original
ROMs and pre-Fat40 BASIC 4, 40 and 80 column
systems are invited to try the tests. I suspect that
the results will be the same. However, simple as it
is, I just don't know how the whole thing will behave
in anotherr PET. The concept of null input might
be handled differently Ffe and, together with POKEing
two system locations, it might crash the PET. This
two system locations, it mi ght cras h the PET. T hi s
mi ght mean it will need to be reset. There is no
might mean it will need to be reset. There is no
way of telling until you join the fun.
Screen input, as described in thiss article, is
most valuable in thee systems prior to 4.0 BASIC as
it shows yet anotherr way of minimizingg characterr
string handlingg in our questt towards a garbageless
PET. My method is limited , however, to onl y certain
PET. My method is limited, however, to only certain
applications. The entire problem was explained
ed
a nd a more gene ral proced u re was proposed by
and a more general procedure was proposed by
Jim Butterfield in COMPUTE!, September, 1981, 1,
##10. I O. BASICC 4 users, ooff course, don't sufferr fromm
these problems.
T he reason I became inte rested in screen
The reason I became interested in screen
input is twofold. . First. First, the suggestion aappears in
the POWERW E R T~
manual, aand it made me curious
about the method's mutility. [POWER is a chil) chip which
add, several commands 10 BASIC. It is sold b), ProJessional
adds several commands to BASIC. It is sold by Professional
SoJlware.] Software.] Secondly, I have a very nice ddisk utility
which displays all the sorts of data about the con­
tents ooff the noppy. floppy. TThe program carefullyy displays
that information by use of ordinary PRIXT NT state tements
(no reverse fi eld , no cursor controls, nothing,
ments (no reverse field, no cursor controls, nothing.
just plain letters). I needed to lift this data, put it
just plain letters). I needed to lift this data, put it
into va riabl es, a nd use it for other things, not ex­
into variables, and use it for other things, not ex
cluding a sorted n listing. It seemed like a simple
task, until a seven minute long garbage collection
tas k, until a seven minute lo ng garbage colleclion
za pped me duri ng testing.
zapped me during testing.
The T garbage collection
occurred because,
although the program originally concatenated
although the program ori ginall y concatenated
(added) ) pieces of strings by use ofo f PRINT I statements
in a loop, as in
ments in a loop, as in
PRINT#4,CHR$(X + +48);
I had to change the code to
I had to change the code to
V$