See also: part 1, part 2, part 3, part 4 and part 5.

The prolific Jim Gerrie recently posted a video of an MC-10 bouncing ball demo he wrote in BASIC:

Thanks to Jim, the MC-10 joins a long list of 80’s home computers that thought bouncing a ball around the screen was a good demo.

Seeing his demo inspired me to revisit my Benchmarking BASIC series and see if we can expand on this.

I begin with the excellent (and free) Xroar Emulator. For those that want to play along, there is now a web browser version you can try without installing anything, or you can try the original JS Mocha emulator. Both should be more than enough for this experiment.

First, I load up my BENCH.BAS framework so I can do some speed tests. It looks like this:

0 REM BENCH.BAS
5 DIM TE,TM,B,A,TT
10 FORA=0TO3:TIMER=0:TM=TIMER
20 FORB=0TO1000
70 NEXT
80 TE=TIMER-TM:PRINTA,TE
90 TT=TT+TE:NEXT:PRINTTT/A:END

The above sample code will run four tests (0 to 3) and each time it will do “something” 1001 times (0 to 1000) and report the results in CoCo TIMER values (where each number represents 1/60th of a second, give or take). The benchmark code would go between lines 20 and 70.

Let’s see how big of an object we want to display. Using Jim’s video as a reference (where he shows some of the BASIC source code), it looks like 8 characters wide by 9 characters tall:

Based on him using substrings going up to 6, it looks like he may have 7 frames of animation (0-6). Impressive. But let’s just start with displaying 8×9 characters in various ways to see how fast we can do it.

The fastest way in BASIC is to use a PRINT@ statement, so my first test is to see how long it takes to print these characters 1001 times. I will hard-code the location for each line starting with 0 (the top left of the screen). It looks like this:

30 PRINT@0,"12345678";:
   PRINT@32,"12345678";:
   PRINT@64,"12345678";:
   PRINT@96,"12345678";:
   PRINT@128,"12345678";:
   PRINT@160,"12345678";:
   PRINT@192,"12345678";:
   PRINT@224,"12345678";:
   PRINT@256,"12345678";

Running that in the benchmark program results in 3986.

Using decimal values is slow, so next I changed them to hex:

30 PRINT@&H0,"12345678";:
   PRINT@&H20,"12345678";:
   PRINT@&H40,"12345678";:
   PRINT@&H60,"12345678";:
   PRINT@&H80,"12345678";:
   PRINT@&HA0,"12345678";:
   PRINT@&HC0,"12345678";:
   PRINT@&HE0,"12345678";:
   PRINT@&H100,"12345678";

Parsing a hex value is much faster, so this results in 3018. That’s about 25% faster.

And, using variables is even faster, since no parsing is required. A quick test that sets variables I-Q to each value, then does a PRINT@I through PRINT@Q produces 2940. Not a huge gain, but every little bit helps. That’s probably the fastest one can print something like this in BASIC.

The problem with using multiple variables is you have to update each one every time the object moves. If you just use one variable, and do math for all the other lines, you are doing the same math for each line that would have been done for the variable.

At this point, we need to see which way of doing math is faster. Or, perhaps, maybe we can do it without using math. . .

To be continued…

Over in the CoCo Facebook group, Diego Barzio just posted a note about discovering some BASIC program line comments that had left out the REM keyword at the start. Because those lines were never the target of a GOTO, there was no error. This had the side effect of saving a byte (or two, since most do “REM ” at the start) for comment lines.

This made me think about what was going on. BASIC will allow you to type in anything, and will try to parse it (to tokenize the line) and produce an error (?SN ERROR, etc.) if there is a problem. But, when you are typing in a line, this BASIC doesn’t check anything until that line is actually ran in the program. (Other versions of BASIC will check when you hit enter. Didn’t the Apple 2 do that?)

REM

In an earlier article, I mentioned that “REM” tokenized into one byte, and the apostrophe (‘) turned into two bytes because it was “:REM(space)” allowing you do do something like this:

10 REM This is a comment.
20 'This is a comment

Since most folks type “REM(space)”, using the apostrophe without a space after it takes the same room. But if you include the space:

10 REM This is a comment
20 ' This is a comment

…that would make line 10 take one byte less (REM + space is two bytes, versus ‘ + space which is three bytes).

Now, if you do not include REM or apostrophe, you can save a byte or two for each comment. If you program has 50 lines of comments, that’s 50-100 bytes.

BASIC Keywords

However, this made me realize that leaving out the REM would cause it to try to tokenize the line, and turn any BASIC keyword into a token, saving even more memory. If your comment included words like PRINT, OR, ELSE, etc., you’d save even more room!

As you can see, because this comment uses the word PRINT (five characters), the version without the REM appears to save six bytes — it saves the apostrophe (two bytes, or would save “REM(space)” for two bytes) plus tokenizes the PRINT keyword down from five bytes to one (saving four more bytes).

Interesting BASIC interpreter abuse, isn’t it? As long as you never run this line, you might save memory by leaving our REM (depending on if you use any keywords). I could imaging comments saying “SHOW THE USER NAME” changed to “PRINT THE USR NAME” to tokenize two words (PRINT and USR).

You would still need REM at the start of the code for any initial comments, and during the code, but for subroutines you could do this:

10 REM THIS IS MY PROGRAM
20 A$="HELLO, WORLD!":GOSUB 1010
999 END
1000 PRINT THE MESSAGE
1010 PRINT A$:RETURN

The GOSUB jumps to 1010 and can find it, and since the program would END before reaching 1000, that would work.

With great power comes great responsibility. Use this wisely :) and thanks, Diego, for noticing this.

Until next time…