Add basic LCRNG

tools/js/lcrng.js

@@ -0,0 +1,31 @@
+class LCRNG {
+  constructor(seed = 0, add = 0x6073, mult = 0x41c64e6d) {
+    this.seed = seed;
+    this.add = add;
+    this.mult = mult;
+  }
+
+  get high() {
+    return this.seed >>> 16;
+  }
+
+  get low() {
+    return this.seed & 0xffff;
+  }
+
+  next(adv = 1) {
+    for (let i = 0; i < adv; i++) {
+      this.advance(this.seed, this.add, this.mult);
+    }
+    return this.seed;
+  }
+
+  next16(adv = 1) {
+    return this.next(adv) >>> 16;
+  }
+
+  advance(seed = this.seed, add = this.add, mult = this.mult) {
+    this.seed = ((Math.imul(seed, mult) >>> 0) + add) >>> 0;
+    return this.seed;
+  }
+}