Section 2 - Commodore Computers

May. JIAov, 1982. 1Q82,lssue Issue 24 COMPUTEI COMPUTEt 141
310PRINTTAB(I0);"
TAB (10);"1"
320 PRINT TAB (10);"1"
330 PRINT TAB (10);"1"
340 PRINT TAB (10);"1"
350 PRINT TAB (10);" 1"
360 PRINT TAB (10);" 1"
370 PRINT TAB (10);"1"
380 PRINT TAB (10);"1"
390 PRINT TAB (10);"1"
400 PRINT TAB (10);"1"
or alternatively you could code:
300 FOR X = 1TO11 I II
310 PRINT TAB (10);"!"
1"
320 NEXT X
Again, the same results are achieved, butthe the
FOR/NEXT loop yields s a savings of 118 li S bytes!
Overlaying
You can n sometimes es conserve memory by overlays.
If your program runs in two separate and distinct
phases (that is, one portion of your program completes
all its work and then is never executed again)
it should be possible to LO split your program into inLO two
sections. Have the last t statement in the first section
issue the statement "LOAD PHASEII" (assuming
your second phase is named "PHASEII"). "PHASEIl"). When
the first section completes its job. job, the last instruction
would load the next phase for execution.
This assumes that you have.written PHASEII PHASEIl
ontoo nLO the cassette tape immediately after PHASEI.
\.
This is called overlaying; it lends itself well to LO a diskoriented
system, but there is no reason not to use it
with tape also. You should be aware that any vari­
disk-
ables used in the first phase will not be available in
the second phase. (However, even though this
should work, the author has not yet been able LO to do
this successfully.
If you still need memory, you may be able to LO
put some of the data used in your program on a
casselle cassette tape and read the data in during program
execution. This technique will involve your writing a
special program to create the data tape, but, in
some instances this cann yield substantial memory
savings. The premier issue of Home e a.nd and Educational
Edu.ca.tiona.l
COJII/PUTINC' COMPUTING! contained an excellent article by
David Malmberg entitled "Custom Characters for
the VIC." A program shown in that article lends
the VIC." A program shown in that article lends
itself very well to illustrating this memory-saving
technique.
technique.
That program contained a number of DATA
statements and is shown below:
170 READX:IFX X:IFX> ) o 0 THEN 190
180 FOR X = X XTOX TOX+7 + 7
182 READ) READJ
184 POKE IJ
186 NEXT
190 GOTO 170
190 GOTO 170
340 DATA 7168,24,24,36,60,102,66,66,0
350 DATA 7176,124,34,34,60,34,34,124,0
360 DATA 7184,126,34,34,32,32,32,112,0
600 DATA 7376,0,0,0,0,0,0,0,0
610DATA-1
You would have to write a program to write
the data to cassette tape (and ideally you would
the data LO casselle tape (and ideally you would
write the data immediately after the program you
write the data immediately after the program you
saved that will be using g that data). The original
program can be easily modified to create the data
program can be easily modifiedLO create the data
tape and an example could be:
tape and an example could be:
100 OPEN 1,1,2,"DATATAPE"
170 READ X:PRINT#1,X:IFX X:PRINT#I,X:IF X > ) 0 THEN 190
180 FORX X = XTOX+7 + 7
182 t82 READJ: READ): PRINT#1J PRINT#IJ
186 NEXT
190 CLOSE! 1
200 PRINT "DATA " TAPE CREATED"
210 END
340 DATA 7168,24,24,36,60,102,66,66,0
350 DATA 7176,124,34,34,60,34,34,124,0
360 DATA 7184,126,34,34,32,32,32,112,0
600 DATA 7376,0,0,0,0,0,0,0,0
610 DATA-1 DATA-I
You would then substitute substillite INPUT#1 INPUT#I statements
for READ statements in the original program,
but the results would be the same. If you
u
wanted LO to use the concept in Mr. Malmberg's berg'S article
in your ownn program, but needed additional
memory, this technique will provide you with a
significant amount of memory.
TheT modified program would be:
significant amount of memory.
165 OPEN l,l,0,"DATATAPE"
I,I,O,"DATATAPE"
170 INPUT#I, INPUT#1,X:IFX ) > OTHEN 0 190
180 FORX X = TOX+7
+ 7
182INPUT#IJ
INPUT#1J
184 POKE I,) IJ
186 NEXT
190 GOTO 170
340 REM -NO DATA STATEMENTS-RESULTS IN
350 REM -A SIGNIFICANT REDUCTION IN
MEMORY
Let's assume that you have exercised all the
memory-saving procedures outlined and your
program still requires additional memory. The last
thing to do is carefully investigate the logic of your
program. Are there statements that are never
executed (perhaps left over from an initial idea
that was abandoned)? Naturally, you should remove
them. Are there better ways LO to implement a procedure
that might reduce the number of instructions