Merge pull request #2 from MindfulMinun/next

Add rng.ts

rng.ts

@@ -0,0 +1,94 @@
+import { swap } from './iterable.ts'
+
+/**
+ * The base class for creating a (potentially seeded) random number generator.
+ * Provides a plethora of methods for manipulating objects with randomness.
+ * (I predicted you might need them, you are not random)
+ * 
+ * Take a look at [this list of JavaScript PRNGs](https://github.com/bryc/code/blob/master/jshash/PRNGs.md)
+ * for guidance on implementation.
+ * @author MindfulMinun
+ * @since 2022-07-08
+ */
+export abstract class BaseRNG implements Iterable<number> {
+    /**
+     * This is the main number generation function.
+     * It should return a number between 0 (inclusive) and 1 (exclusive) as well as update its internal state.
+     */
+    abstract nextValue(): number
+
+    /** nyanyanya */
+    *[Symbol.iterator]() {
+        while (true) yield this.nextValue()
+    }
+
+    /** Returns a floating point number between 0 (inclusive) and 1 (exclusive) */
+    float() {
+        return this.nextValue()
+    }
+
+    /** Returns an integer between the provided bounds. This returns integers *up to* `upper`, without including it. */
+    int(upper: number): number
+    int(lower: number, upper: number): number
+    int(a: number, b?: number): number {
+        const rand = this.float()
+        const [min, max] = typeof b === "undefined" ? [0, a] : [a, b]
+        return Math.floor(rand * (max - min + 1) + min)
+    }
+
+    /** Chooses a random element from a provided array */
+    choose<T>(arr: T[]) {
+        return arr[Math.floor(this.float() * arr.length)]
+    }
+
+    /** Shuffles an array */
+    shuffle<T>(arr: T[]) {
+        let i, j
+        for (i = arr.length - 1; i > 0; i--) {
+            j = Math.floor(Math.random() * (i + 1))
+            swap(arr, i, j)
+        }
+        return arr
+    }
+}
+
+/**
+ * A simple RNG which returns numbers generated by {@link https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Math/random Math.random}
+ * @author MindfulMinun
+ * @since 2022-07-08
+ */
+export class Random extends BaseRNG {
+    nextValue() { return Math.random() }
+}
+
+/**
+ * A seeded RNG which implements Mulberry32
+ * @author MindfulMinun
+ * @since 2022-07-08
+ */
+export class Mulberry32 extends BaseRNG {
+    #seed!: number
+    originalSeed!: number
+
+    constructor(seed = Date.now()) {
+        super()
+        this.resetSeed(seed)
+    }
+
+    /** Resets the seed */
+    resetSeed(seed = this.#seed) {
+        this.originalSeed = seed
+        this.#seed = seed
+    }
+
+    nextValue() {
+        // Mulberry32
+        let a = this.#seed
+        a |= 0
+        a = a + 0x6D2B79F5 | 0
+        let t = Math.imul(a ^ a >>> 15, 1 | a)
+        t = t + Math.imul(t ^ t >>> 7, 61 | t) ^ t
+        this.#seed = a
+        return ((t ^ t >>> 14) >>> 0) / 4294967296
+    }
+}