melsloop.com
>The author, who was asked to find a bug in Mel's code, encountered a peculiar loop (a section of code that repeats itself). This loop didn't seem to have a condition that would stop it, which is unusual because without such a condition, a loop would run indefinitely, making the program stuck.
>Now, a feature of the RPC-4000 computer they were using was something called an index register. In layman's terms, it's like a helper that allows you to easily go through a series of data one piece at a time. But Mel never used it. Instead, he had a complicated way of going through the data himself.
>The author noticed something strange about how Mel was handling the data: he was putting it near the "top" of the computer's memory. When he was done with the last piece of data, he would increment the address, but because it was already at the top, it couldn't go higher. This caused something called an overflow, which is a bit like trying to put more water into a full glass, causing it to spill over.
>This overflow didn't cause an error, though. Instead, it added one to the operation code of the instruction, effectively changing it to a "jump" instruction. A "jump" instruction in programming is like a command to skip to another place in the code. In this case, it made the program skip to the beginning of the code, letting it escape the loop and continue running smoothly.
>In short, Mel created a loop that appeared endless, but he ingeniously designed it to escape itself by using a memory overflow. This trick was hidden deep in the machine code, making it hard for others to understand, but effectively doing what Mel wanted.