Section 2 - Commodore Computers

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necessary to accomplish some objective? Sometimes necessary to accomplish some objective? Sometimes being able to buy back just five or ten bytes of memory will allow your program to run. One final poiI1l; point; there are instances when you have worked forr hours on a large, complicated program and you decide to save it on a cassette tape. You type in the command "SAVE MY- tape. Yo u type in the com ma nd "SAVE MY PROGRAM", press ENTER, and 10 and behold, PROGRAM". press ENTER, and lo and behold, instead of receiving the message to press the play and record bultons, buttons, youu instead get the message "OUT OFF MEMORY." This is one of the most frustrating events possible when writing a proggram because youu do not want to lose the hours of effort n alreadyy expended. . Try issuing the "SAVE" V command with a shorter filename; this usually ua y works. Instead of entering "SAVE MY MY- PROGRAM", use "SAVE A". PROGRAM ", use "SA VE A". It ta kes some effon, but using the techniq ues It takes some effort, but using the techniques outlined here couldd mean the difference between being able to do what you want with your VIG20 VIC20 or being cOlllinuously continuously confronted nted with an out of memory condition. n. With a lillie little patience you u might g be' able e to find that needle in the haystack. If all else fails, don't give up hope. Remember that your VIG20 VIC20 has the capability ity of being ex- panded to 32K! © panded to 32 K! © AATTENTION *VIC 2 0 OWNERS *VIC 2O OWNERS @ilJ.%.INI'jf'1\!l1i\ill iQ),%, 'jf'.%. OINl«:;;©IRlIll'©IRl.%. 'jf'~iQ) "THE PERIPHERAL PEO PLE" "THE PERIPHERAL PEOPLE'1 Makers of the following quality add-ons for the VIC 20' Makers of the following quality add-ons for the VIC 20* RAM Memory ExpanSion Expansion from OK to 64K 64 or 80 Cotumn Column Video Expansion PROM Simulator for saving programs in power-off mode 21-Key Numeric Pad for high speed data entry 3 Position ExpanSion Expansion Chassis PROM Programmers and PROM I ROM ExpanSion PROM Programmers and PROM/ROM Expansion AND MORE!!! Ask your local <strong>Commodore</strong> Oea~ Dealer aabout our products or phone orr write for Free Catalogue: a QUANTUM 3001 Redhlll RedhillAve Bldg 4. SUlle Suite 105 DATA. INC. Cosla Costa Mesa. CA 92626 (714) 754-1945 Dealel Dealer inQUiries inquiries welcomed LETTER QUALITY PRINTERS $99500 BELIEVE IT! AND CHECK THE FEATURES • WORKS WITH ANY WORD PRO. SOFTWARE • 132 COLUMN PLATEN • 45 CHARACTERS PER SECOND • USES STANDARD DAISY PRINT WHEELS FOR TYPE STYLE VARIETY • PROPORTIONAL SPACING • TRACTOR AVAILABLE • COMPLETELY RECONDITIONED •.90 DAY WARRANTY • WE PAY SHIPPING IN U.S. • WE PAY SHIPPING IN U.S. ADD M7500 ' 175" FOR APPLE OR TRS-80 INTERFACE tNTERFACE (PARALLEL) ADD *279°° ' 279" FOR PET/CBM PETI INTERFACE tNTERFACE (IEEE-488) (tEEE-488) ~ .. ORDERS ACCEPTED D BY PHONE NO COD'S (716) 625-8200 INTERNATIONAL DEPT. C-5 2521 NIAGARA NtAGARA FALLS BLVD. PO BOX 151, NO. TON., NY 14120
May, 1982. 1982, Issue l$Sue 7& 2.4 COMPUTE! COMPUTlI 143 Considering Considering SpaceAnd Time In The Atari Atari C Michael Levy and G rant Levy C. Michael Levy and Grant Levy Gainesville, FL Would you like to know how to speed up some of your programs, or make them use up less memory? As everyone comes to learn as they gam gain experience in m programming, programmmg, small and often very subtle changes cha.nges in even very simple programs can n have major consequences. Consider the following owing four programs. Each has exactly y 1000 lines. Each makes two references to variable B, 994 assignments to variable vanable A, contain six GOSUBs COSUBs and six RETURNs, one POKE, one PEEK, one PRINT and one STOP. They all achieve the same end: they determine that the value of variable A is zero and print the number of clock ticks (each lasting l/60th 1I60th sec.) required for execulIon of the program. They are equivalent, execution of the program. They are equivalent, right? n glll' Wrong! W1"Dllg! Programs 1I and 2 each require about 15000 bytes of memory, nearly 66% more than the ap bytes of memory, nearl y 66% more than the approximately 9100 bytes required for Programs 3 and 4. The reason for this is the way Atari BASIC handles constants and variables. Each and every reference to a constant (zero, in these programs) consumes seven bytes. This is true even if the statements using those constants are never executed in the program. (as are lines 2-994 in Program 1I and hnes lines 8-1000 I in In Program 2). Programs 3 and 4 involve v?lve the ~ssi.g assignment e nt of a constant to only one vanable variable (B 111 in llIle line I); 1); variable A assumes its values by reference to this value. Each such reference requires onlyy one byte. . So the first lesson is to use constants sparingly, If at all. Develop a schema for assigning variable if at all. Develop a schema for assigning variable names to constants so that youu will not confuse them with "real" variables. For example, consider them with "real" variables. For example, consider DO = 0, 0 I = I , or CO = 0, C I = I , etc. where the DO = 0, D1 = 1, or CO = 0, C1 = 1, etc. where the symbol "D" is a mneumonic for digit or "C" reminds symbol "0 " is a mneumonic for digit o r "C" reminds you that it is a consta:nt. constant. Any other combination of letters andlor and/or digits could then represent variables which V{I1),. vary. Speed DIfferences Differences While Programs I 1 and 2 are identical in memory requirements, and Programs 3 and 4 are also iden requirements, and Programs 3 and 4 are also iden tical to each other in terms of memory, these pairs of programs are vastly different in execution execUlion speed. Here we find that Programs 2 and 4 each require only y one clock tick for completion. In marked contrast are Programs 1 and 3 which are 42 times contrast are Programs I and 3 which are 42 times slower! slower! The reason for this enormous discrepancy is the way that Atari Atan BASIC seems to locate subroutines. BASIC is apparently incapable of immediately jumping Jumping to the desired line referenced in a GOSUB. COSUB. Rather, it appears to start from the first line of or the program, and sequentially search through the list pl:o,gram , and sequentially sea rch through the list of lines hnes until unlIllt it finds what it wants. Thus, in Programs 3 and 4, when it encounters in line 1000 a GOSUB COS U B 999, it must begin at line one and look at each of the 998 intervening lines until it reaches 999. There, it encounters a GOSUB COSUB 998. Back to the top of the list it goes, fruitlessly examining 997 lines. And so on. BASIC performs the same sequence of steps in Programs 2 and 4, but it obviously has to do fewer of them, since all of the subroutines are near the top of the list of line e numbers. Thus the second lesson, is to place subroutines as close as possible to the beginning of or each program. Some of your programs that heretofore seemed to drag on unmercifully could now have more zip. And, finally, we answer the question n that has been bothering you for some time. No, we are not masochists. We did no/ not type in 1000 lines of code in order to perform these benchmark tests. Instead, , a one-line program was written to create a 1000-line skeleton for Programs 1I and 2: 10 OPEN #2,8,0,"D:PROGRAM : FORJ= FOR] = 1 TO 1000 :?? #2J;" " A=O": A = 0" : NEXT]: J : CLOSE #2 . Then PROCRAM was ENTERed, the approp Then PROGRAM was ENTERed, the approp riate n minor mlllor changes made to only seven lines, and then RUN. The same procedure was followed for then RUN. The same procedure was fo llowed for Program 1. 1 POKE 20,0 : B=O B = 0 ,GOSUB : 1000, : B=PEEK(20) B = :?B:STOP: ? B : 2 A=O A = 0 3 A=O A = 0 4 A=O A=0 5 A A=O = 0 6 A=O A = 0 7 A=O A = 0 8 A=O A = 0 9 A=O 9 A = 0 ere. etc. 995 A=O: A = 0:RETURN 996 GOSUB 995 : RETURN 997 GOSUB 996 : RETURN 998 GOSUB 997 : RETURN 999 GOSUB 998 : RETURN GOSUB 995 : RETURN GOSUB 996 : RETURN GOSUB 997 : RETURN 999 GOSUB 998 : RETURN 1000 GOSUB 999: RETURN
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Section 2 - Commodore Computers

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