Zero Lines Maze: What the 8-Bit Guy's One-Liner Can Still Teach Us
Recorded: May 28, 2026, 4:03 a.m.
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Zero Lines Maze: What the 8-Bit Guy's One-Liner Can Still Teach Us - Retro Game Coders Skip to main content Skip to header right navigation Skip to site footerRetro Game CodersRetro computer/console game + dev communityMenuSearch...Search siteSubmit searchAboutRetro Computer CollectionContactBlogRetro ResourcesRetro Gaming TimelineOnline Retro IDERetro Pixel Art EditorDungeon Loom Map Editor6502 Programmer’s ReferenceEmulatorsAcorn ElectronAmstrad CPC EmulatorOnline BBC Micro EmulatorCommodore PET EmulatorBrowser C64 EmulatorDOSBox/DOS PC emulatorTandy CoCo/DragonBest Retro YouTube ChannelsNew Retro BooksRaspberry Pi Amiga EmulationMiSTer FPGA TutorialBMC64 C64 PiCommunitysearchSearch siteSubmit searchHome » Retro Game Coders Blog » ProgrammingZero Lines Maze: What the 8-Bit Guy’s One-Liner Can Still Teach UsWhat can we learn from 8bitguy’s version of the famous C64 BASIC random maze …?Say what you will about the 8-Bit Guy, but he just put out a fantastic take on the famous one-liner maze program. Even though I have typed that one-liner more times than I can remember, it still inspired me to write this post today, decades after I first learned it.Yep, the 8-Bit Guy, controversial as he is, sent me down a proper several day rabbit hole. There are at least four genuinely useful tricks hiding in his final program, but his video does not have a written version from what I can tell, so let me take you through them here. Join the Retro Game Coders CommunityHow the 10 PRINT Maze (Famous Version) WorksHere is the original: 10 PRINT CHR$(205.5+RND(1)); : GOTO 10Run that on a C64 and you get an endless, scrolling random maze. It looks like magic. It is actually one of the most elegant little hacks in 8-bit BASIC. Many people have “riffed” on it, which was probably best done by Robin.The whole thing is based on this guy CHR$(205.5+RND(1)).RND(1) hands you a float between 0 and 0.999, so the result lands somewhere between 205.5 and 206.499. CHR$ ignores the fraction, so you get character 205 or character 206, at roughly 50/50 odds. Those two codes are the diagonal PETSCII graphics, the / and \ lines.Print one or the other at random, let the screen scroll, and the diagonals join up into a maze. As 8 Bit Guy says, it looks a bit nicer on the Vic 20 font because it joins up better.There’s no logic so it fits on one line. It’s a bigger deal than you would think, even today it is worth eliminating IF statements. This code shows you can fold a random binary choice into a single expression with zero branches, and combined with the C64’s habit of truncating floats, and a coin-toss is done for you.It’s famous now but it was originally straight out of the manuals shipped with the C64 and the VIC-20 back in 1980s, which is where a lot of us grey beards first met it.You can now follow the tutorials and edit the code right in your web browser with the Online Retro IDE– No downloads, configuration, etc necessary, and it is free!Random Maze 8Bit Guy Version – *Zero* Lines!The 8-Bit Guy’s first nerd flex is making it shorter than one line. What??Two things go into making that work:You can run a FOR ... NEXT loop straight at the BASIC prompt (direct or REPL mode I guess in today’s speak), no line number needed. It will happily execute a whole loop.STEP 0 is legal, which means the counter never advances, so the loop never ends. I always assumed it would error so never tried it, d’oh! Put them together and you get an infinite maze with zero program lines: FOR A=0 TO 1 STEP 0:PRINT CHR$(205.5+RND(1));:NEXTI have to say STEP 0 as a deliberate infinite loop is one of those things that feels like cheating the first time you see it. It is the kind of trick worth keeping in your back pocket similar to WHILE (1) in C.Three Speed OptimisationsAs if that wasn’t enough knowledge to drop, the second half is a speed build, and this is where there are even more nuggets of wisdom:💬 Questions or comments? Head over to the community to discuss!Random from the SID, not from RND.RND is slow no matter how you call it. Voice 3 of the SID can be set to a noise waveform, and once it is running, the top oscillator register gives you a fresh pseudo-random byte every time you read it: POKE 54287,255 : POKE 54290,128 : REM voice 3 = noise PEEK(54299) ... : REM random 0-255, fast Reading a hardware register beats computing a float. Lovely example of using the chip you already have instead of the maths library.Precompute with Lookup TablesThis will be more familiar to RGC readers, and that is LUTs or Lookup Tables.Converting a number to its binary digits on the fly is expensive. So the program spends a moment at startup building a string that maps every value to its binary representation. After that, turning 42 into its bits is just an array lookup, with no calculations necessary. Precompute once, fetch quickly forever after. This pattern shows up everywhere from sine tables to colour ramps, and it is one of the go-to habits in optimising 8-bit work.Swap the Table, Not the Logic.Once you have a table that emits “0” and “1”, you can replace those two characters in the table with the two diagonal glyphs, or any character you like. Same approach, different output. Decouple the data from the loop and you can repurpose the whole thing by just editing a string.Full Listing Based on 8 Bit Guy Approach[Edit a copy of the code and see it in action over on my online retro IDE]The main differences here are I set the text colour and show a visible indication that the program is working because otherwise it takes so long it might seem to have frozen! |
The analysis of the 8-Bit Guy’s approach to the Zero Lines Maze reveals several sophisticated programming and optimization techniques derived from legacy systems. The original maze utilized an elegant hack based on the expression CHR$(205.5+RND(1)) to generate scrolling diagonal characters, which exploits the behavior of the Commodore 64 and VIC-20 systems. This technique leverages the fact that RND(1) produces a float between 0 and 0.999, and the system truncates the result, effectively yielding character codes 205 or 206, which correspond to the diagonal graphics lines used for scrolling. This method demonstrates how a seemingly simple random choice can be folded into a single expression, eliminating the need for conditional logic and fitting the design into a single line of BASIC code. The 8-Bit Guy further demonstrated brevity by employing a structure that allows for infinite looping without needing line numbers, specifically by using a FOR ... NEXT loop with a step value of zero, which results in an infinite loop and is presented as a mechanism for advanced control. This showcases a trick applicable to modern programming, suggesting the value of deliberately designed infinite loops, similar to the WHILE (1) construct in languages like C. Beyond the initial concept, the discussion pivots to advanced speed optimizations that provide deep insights into hardware interaction and data representation. One key optimization involves accessing pseudo-random data directly from hardware registers, such as the SID chip, rather than relying on floating-point mathematics, as reading a hardware register is significantly faster than performing complex calculations. Another crucial optimization strategy is the use of Lookup Tables (LUTs) to avoid expensive on-the-fly conversions of numbers to their binary representations. By precomputing character mappings or color ramps at startup, subsequent data retrieval becomes a simple array lookup, drastically improving performance. Furthermore, the principle of decoupling data from the operational logic is highlighted, suggesting that data structures can be repurposed. Instead of hardcoding logic for different outputs, the data itself can be manipulated—for instance, by replacing characters in a precomputed table with diagonal glyphs—to achieve diverse visual effects. The full listing demonstrated this by using arrays and POKE commands to populate a matrix based on the generated sequence, illustrating a highly optimized method for rendering the maze structures. Finally, the analysis concludes with a critical perspective on bottleneck identification. The 8-Bit Guy’s optimization process revealed that the limiting factor in achieving the fastest result was not the interpreter or the BASIC logic itself, but rather the inherent speed of the hardware screen-scroll operation. This underscores the fundamental principle in system optimization: accurately profiling the execution to identify the true performance bottleneck before attempting systemic changes, such as migrating to assembly language, ensuring that optimizations are targeted where they yield the greatest performance gain. |