ram_simulator_rust is a simple Register Machine simulator written in Rust. It supports hardcoded programs and executing files via its cli. By default, it outputs all registers (up to the highest that was used) after executing every instruction.

The instruction set is the one described in lib/ram_simulator/src/instruction/mod.rs. (Basically the one from my Computability and Complexity course with one minor addition.)

For the instruction set, see lib/ram_simulator/src/instruction/mod.rs.

Here's an example program that computes floor(ld(c(1))) (the floor of the log_2 of the value that is in the 1st register):

INIT 256 ; Initialize the 1st register with 256 CLOAD 0 ; this is line 1 (not 2, the initialisation is **not** counted) STORE 2 CLOAD 1 STORE 3 LOAD 3 SUB 1 IF c(0) > 0 THEN GOTO 15 LOAD 2 CADD 1 STORE 2 LOAD 3 CMULT 2 STORE 3 GOTO 4 LOAD 2 ; even though this is technically line 16, GOTO 15 jumps here CSUB 1 STORE 1 END

The INIT instruction is my own addition. It initializes the first n registers with the given values. For example, to set c(1)=5, c(2)=3, c(3)=2, you can use INIT 5 3 2. Every program must start with this, even if it's not used/empty.

Note: For hardcoded programs, look at src/examples/example{1,2}.rs.

• Empty lines between instructions are currently not supported.
• Comments are supported on any line via any delimiter (e.g. #, //, ;, --, /* */, --[[ ]]--, etc.), except on INIT, as long as there's at least one space between the comment and the instruction.
• IF's syntax is matched using a regex and is intentionally not very strict. The number of whitespaces doesn't matter either. The following get parsed as the exact same instruction:

  IF c(0)>0 THEN GOTO 15 IF c(0) > 0 THEN GOTO 15 ; if you write code like this, IF c(0)> 0 THEN GOTO 15 ; you're a menace to society though IF c(0) >0 THEN GOTO 15 IF c(0) > 0 THEN GOTO 15

• The maximum number of registers is 1024 by default.
  • You can change this in lib/ram_simulator/src/state.rs.
  • It still can't be more than usize::MAX though.
• The values of the registers are unsigned 128-bit integers (u128).
  • You can change this in lib/ram_simulator/src/state.rs.

• If you have an endless loop in your code, the simulation may crash your browser tab, or make it appear unresponsive, if you set max depth too high.
• Specific errors on which the parser panics cannot be shown on the page via javascript. There is currently only one generic error. Done. All parser errors now get propagated to rswasm, which then shows them on the page.

1. Get the rscli binary
   • Build the project with cargo build --release. The binary will be in target/release/rscli, or
   • Grab the latest release
2. (optional) Install the binary
   • Linux: sudo install -m 755 target/release/rscli /usr/local/bin/rscli
   • Windows: i don't know, figure it out
   • MacOS: ¯\_(ツ)_/¯
3. Execute a program
   • Continuous mode: rscli c /path/to/program.s
   • Step-by-step mode: rscli s /path/to/program.s

• See georgar.de/projects/rswasm

Note: The WASM interface is not fully-featured yet, see Limitations.

The project consists of the ram_simulator library, the rscli command line interface, and the ram_webassembly WebAssembly Interface (as a library).

• rscli is licensed under GNU GPL v3
• ram_simulator is licensed under GNU LGPL v3
• ram_webassembly is licensed under GNU LGPL v3