Yet another virtual machine
Hey. It's been a month since my last journal. That's long. Lots of us seem to be posting like this these days.
Work continues well. It has been a big shift from being a solo hobbyist developer to working on a real project as part of a (admittedly small) team but I was kind of prepared for the differences through listening to guys on here over the years and seem to be adjusting okay.
Since I'm working on something real now, I decided that I wanted a home project that was just purely for fun and had no real purpose. I've always been interested in compilers and virtual machines and have written a plethora of scripting languages, but never written a VM that supported dynamic allocation in a heap and a language that took advantage of it.
So that's what I'm doing. The following assembler script calculates the length required to concatenate two strings, allocates it, copies the data in the outputs the result plus the size of the new buffer, then frees it. The contents of the memory location labelled 'name' dictates which second string to use.
setax string0 strlen push setax name get movra strlen push add pop incrx alloc movar movad setax store put setax string0 strlen copy push setax store get push add pop movrd setax name get movra strlen incrx copy setax store get movra outs strlen outn setax end outs setax store get movra free exit store: 0 name: string2 string0: "hello world from " 0b string1: "paul" 10b 0b string2: "eric" 10b 0b end: 10b 0b
Horrible, isn't it? But it isn't really designed to be human written, this is just testing the VM works properly. It's really more designed to target a compiler at. I've decided though that this compiler is going to compile via text assembly like the above so I can check the output more easily, plus it looks cool.
It's basically a three register VM - a value register and two address registers. Memory is just a contiguous block of chars that contains the program, then the stack, then the heap. Heap management is currently just a case of storing free blocks in a vector and merging adjacent free blocks together but more than ample for what I need.
So all good fun, largely because it is pointless and complicated.