Data commit

Task/Elliptic-curve-arithmetic/Java/elliptic-curve-arithmetic.java

@@ -0,0 +1,87 @@
+import static java.lang.Math.*;
+import java.util.Locale;
+
+public class Test {
+
+    public static void main(String[] args) {
+        Pt a = Pt.fromY(1);
+        Pt b = Pt.fromY(2);
+        System.out.printf("a = %s%n", a);
+        System.out.printf("b = %s%n", b);
+        Pt c = a.plus(b);
+        System.out.printf("c = a + b = %s%n", c);
+        Pt d = c.neg();
+        System.out.printf("d = -c = %s%n", d);
+        System.out.printf("c + d = %s%n", c.plus(d));
+        System.out.printf("a + b + d = %s%n", a.plus(b).plus(d));
+        System.out.printf("a * 12345 = %s%n", a.mult(12345));
+    }
+}
+
+class Pt {
+    final static int bCoeff = 7;
+
+    double x, y;
+
+    Pt(double x, double y) {
+        this.x = x;
+        this.y = y;
+    }
+
+    static Pt zero() {
+        return new Pt(Double.POSITIVE_INFINITY, Double.POSITIVE_INFINITY);
+    }
+
+    boolean isZero() {
+        return this.x > 1e20 || this.x < -1e20;
+    }
+
+    static Pt fromY(double y) {
+        return new Pt(cbrt(pow(y, 2) - bCoeff), y);
+    }
+
+    Pt dbl() {
+        if (isZero())
+            return this;
+        double L = (3 * this.x * this.x) / (2 * this.y);
+        double x2 = pow(L, 2) - 2 * this.x;
+        return new Pt(x2, L * (this.x - x2) - this.y);
+    }
+
+    Pt neg() {
+        return new Pt(this.x, -this.y);
+    }
+
+    Pt plus(Pt q) {
+        if (this.x == q.x && this.y == q.y)
+            return dbl();
+
+        if (isZero())
+            return q;
+
+        if (q.isZero())
+            return this;
+
+        double L = (q.y - this.y) / (q.x - this.x);
+        double xx = pow(L, 2) - this.x - q.x;
+        return new Pt(xx, L * (this.x - xx) - this.y);
+    }
+
+    Pt mult(int n) {
+        Pt r = Pt.zero();
+        Pt p = this;
+        for (int i = 1; i <= n; i <<= 1) {
+            if ((i & n) != 0)
+                r = r.plus(p);
+            p = p.dbl();
+        }
+        return r;
+    }
+
+    @Override
+    public String toString() {
+        if (isZero())
+            return "Zero";
+        return String.format(Locale.US, "(%.3f,%.3f)", this.x, this.y);
+    }
+}