Writing a register based VM in less than 125 lines of C code

• gigatron-rom

  1 219 6.9 C

  System, apps and tooling for the Gigatron TTL microcomputer

• lc3-vm

  3 310 0.0 C

  A LC3 virtual machine implementation in a few lines of C code

I haven't read the whole article yet, I just want to report what seems to be a small error:

> The code is written in C11, and it will probably compile on most operating systems. The repo can be found here, and the exact source code is vm.c:

The link on "here" is broken, it's https://github.com/,nomemory/lc3-vm (with a comma before your github username) instead of (I think) https://github.com/nomemory/lc3-vm.

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• Puts Debuggerer

  3,154 91 5.5 Ruby

  Ruby library for improved puts debugging, automatically displaying bonus useful information such as source line number and source code.

I haven't read the whole article yet, I just want to report what seems to be a small error:

> The code is written in C11, and it will probably compile on most operating systems. The repo can be found here, and the exact source code is vm.c:

The link on "here" is broken, it's https://github.com/,nomemory/lc3-vm (with a comma before your github username) instead of (I think) https://github.com/nomemory/lc3-vm.

• lc3as.py

  1 18 10.0 Python

  An assembler for the LC-3 fictitious computer.

  

Ah the LC-3! I wrote an assembler for it a little while ago: https://github.com/pepaslabs/lc3as.py

I’ll definitely be digging into this article!

• Papers

  2 4 1.8

Further to this: this kind of thing is something the Forth community takes seriously. They call these threaded code techniques. [0] (The Gforth interpreter, for instance, gives you the choice of various different techniques.)

Anton Ertl of Gforth fame published a microbenchmark performance comparison of toy interpreters, written in C, run on various CPUs. [1] As you say, the approach using function pointers (call threading) scores poorly.

Interestingly, direct threading and indirect threading are extremely close, with the winner seeming to depend on the specific CPU. [1] Branch-prediction differences seem to be the main reason. There was a 2001 paper on this. [2]

[0] https://www.complang.tuwien.ac.at/forth/threaded-code.html

[1] https://www.complang.tuwien.ac.at/forth/threading/

[2] https://github.com/ForthPapersMirror/Papers/blob/master/Conv...

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