Data update

Task/Elliptic-curve-arithmetic/JavaScript/elliptic-curve-arithmetic.js

@@ -0,0 +1,90 @@
+class Pt {
+  static bCoeff = 7;
+
+  constructor(x, y) {
+    this.x = x;
+    this.y = y;
+  }
+
+  static zero() {
+    return new Pt(Number.POSITIVE_INFINITY, Number.POSITIVE_INFINITY);
+  }
+
+  isZero() {
+    // same threshold logic as Java version
+    return this.x > 1e20 || this.x < -1e20;
+  }
+
+  static fromY(y) {
+    // cbrt(pow(y,2) - bCoeff)
+    return new Pt(Math.cbrt(Math.pow(y, 2) - Pt.bCoeff), y);
+  }
+
+  dbl() {
+    if (this.isZero()) {
+      return this;
+    }
+    const L = (3 * this.x * this.x) / (2 * this.y);
+    const x2 = Math.pow(L, 2) - 2 * this.x;
+    const y2 = L * (this.x - x2) - this.y;
+    return new Pt(x2, y2);
+  }
+
+  neg() {
+    return new Pt(this.x, -this.y);
+  }
+
+  plus(q) {
+    // point doubling?
+    if (this.x === q.x && this.y === q.y) {
+      return this.dbl();
+    }
+    // handle "point at infinity"
+    if (this.isZero()) {
+      return q;
+    }
+    if (q.isZero()) {
+      return this;
+    }
+    const L = (q.y - this.y) / (q.x - this.x);
+    const xx = Math.pow(L, 2) - this.x - q.x;
+    const yy = L * (this.x - xx) - this.y;
+    return new Pt(xx, yy);
+  }
+
+  mult(n) {
+    let r = Pt.zero();
+    let p = this;
+    // binary double-and-add
+    for (let i = 1; i <= n; i <<= 1) {
+      if (i & n) {
+        r = r.plus(p);
+      }
+      p = p.dbl();
+    }
+    return r;
+  }
+
+  toString() {
+    if (this.isZero()) {
+      return "Zero";
+    }
+    // format with 3 decimal places, dot as decimal separator
+    return `(${this.x.toFixed(3)},${this.y.toFixed(3)})`;
+  }
+}
+
+// Equivalent of the Java `main` method
+(function main() {
+  const a = Pt.fromY(1);
+  const b = Pt.fromY(2);
+  console.log(`a = ${a}`);
+  console.log(`b = ${b}`);
+  const c = a.plus(b);
+  console.log(`c = a + b = ${c}`);
+  const d = c.neg();
+  console.log(`d = -c = ${d}`);
+  console.log(`c + d = ${c.plus(d)}`);
+  console.log(`a + b + d = ${a.plus(b).plus(d)}`);
+  console.log(`a * 12345 = ${a.mult(12345)}`);
+})();