thinstuff

server/utils/random.js

@@ -0,0 +1,80 @@
+/**
+ * Pseudo random number generator
+ * using the xorshift32 method.
+ */
+export class Xorshift32 {
+    /* @type {number} */
+    state;
+
+    /** @param {number} seed */
+    constructor(seed) {
+        this.state = seed | 0;
+    }
+
+    /** @protected Shuffle the internal state. */
+    shuffle() {
+        //
+        // Run the actual xorshift32 algorithm
+        let x = this.state;
+        x ^= x << 13;
+        x ^= x >>> 17;
+        x ^= x << 5;
+        x = (x >>> 0) / 4294967296;
+
+        this.state = x;
+    }
+
+    /**
+     * Get a random number and shuffle the internal state.
+     * @returns {number} a pseudo-random positive integer.
+     */
+    get() {
+        this.shuffle();
+        return this.state;
+    }
+
+    /** @param {number} x @returns {number} a positive integer lower than x */
+    lowerThan(x) {
+        return this.get() % x;
+    }
+
+    /** @param {number} x @reurns {number} a positive integer lower than or equal to x */
+    lowerThanOrEqual(x) {
+        return this.get() % (x + 1);
+    }
+
+    /**
+     * @param {<T>[]} arr
+     *
+     * @return {<T>}
+     */
+    randomElement(arr) {
+        const idx = this.lowerThan(arr.length);
+
+        return arr[idx];
+    }
+
+    /**
+     * @param {...<T>} args
+     * @returns {<T>}
+     */
+    oneOf(...args) {
+        const idx = this.lowerThan(args.length);
+
+        return args[idx];
+    }
+
+    /**
+     * @param {number} lowerThanOrEqual a positive integer
+     * @param {number} greaterThanOrEqual a positive integer greater than lowerThanOrEqual
+     * @returns {number} a pseudo-random integer
+     */
+    within(greaterThanOrEqual, lowerThanOrEqual) {
+        const range = lowerThanOrEqual - greaterThanOrEqual;
+
+        const num = this.lowerThanOrEqual(range);
+
+        return num + greaterThanOrEqual;
+    }
+}
+