collatz-wasm

1. pick a positive integer number
2. a) when odd: 3x + 1
3. b) when even: x/2
4. repeat until you find a number you had before

on positive integers this algorithm (the mathematical equivalent is called Collatz Conjecture) ends always at 1

it is an unsolved mathematical problem, but you could give it a try in the browser or another system which can run wasm with this module ;-)

it accepts any javascript number (internally i32) and gives back an Array of numbers

usage

By installing from npm

npm install collatz-wasm

and by using a bundler you should be able to import it in javascript like this:

import init, { collatz } from "collatz-wasm"

...

init()
   .then(() => {
      collatz(1337)
   })

plans for the future

I plan on adding support for i64 (javascript BigInt), but have not yet reached a proper understanding of Rust Traits to do so. An alternative would be to copy code and replace i32 with i64, but who would do such a thing??

uses

The Collatz Conjecture can be used to plot nice graphs and art, which was a motivation to create this module

building from rust to wasm

install dependencies

First install a rust environment (e.g. rustup) and then install wasm-pack like-a-so: $ cargo install wasm-pack

build wasm bundle

based on this howto: https://developer.mozilla.org/en-US/docs/WebAssembly/Rust_to_wasm

$ wasm-pack build --target web

This builds the rust lib.rs into a file bundle at pkg/ which is ready to be imported into a javascript environment that has wasm support.

using it locally from the git repository

 import init, { collatz } from "./pkg/collatz_wasm.js"
 init()
   .then(() => {
      const list = Array.from(collatz(10))
      console.log(JSON.stringify(list))
   })

test wasm bundle locally

Start a local webserver (e.g. python3 -m http.server) and navigate to index.html to see a test page importing the compiled wasm (open Developer Tools to see result logged in the Javascript console).