## Predictable Random Number Generation in TypeScript

### Lehmer

I got the idea for using this type of RNG from the javidx9 video Procedural Generation: Programming The Universe. It's a really good video as are most of the videos he produces so I recommend you give it a watch. The algorithm he talks about in the video is the Lehmer random number generator.

I'm implementing a simple match the blocks game in TypeScript and I wanted to implement the algorithm mentioned there in TypeScript.

Here's the code:

```
export class RNG {
private static readonly a = 16807;
private static readonly m = 2147483647;
private static readonly q = 127773;
private static readonly r = 2836;
constructor(private _seed: number) {
if (this._seed <= 0 || this._seed === Number.MAX_VALUE) {
throw new Error("Seed out of range.");
}
}
public nextDouble(): number {
const hi = this._seed / RNG.q;
const lo = this._seed % RNG.q;
this._seed = (RNG.a * lo) - (RNG.r * hi);
if (this._seed <= 0) {
this._seed = this._seed + RNG.m;
}
return (this._seed * 1.0) / RNG.m;
}
public nextInt(min: number, max: number): number {
const range = Math.round(max) - Math.round(min);
return min + Math.round(range * this.nextDouble());
}
}
```

You can simply new up an instance and call `rng.nextInt()`

to get a random integer based on the provided seed.