Data commit

Task/Elliptic-curve-arithmetic/Go/elliptic-curve-arithmetic.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+    "fmt"
+    "math"
+)
+
+const bCoeff = 7
+
+type pt struct{ x, y float64 }
+
+func zero() pt {
+    return pt{math.Inf(1), math.Inf(1)}
+}
+
+func is_zero(p pt) bool {
+    return p.x > 1e20 || p.x < -1e20
+}
+
+func neg(p pt) pt {
+    return pt{p.x, -p.y}
+}
+
+func dbl(p pt) pt {
+    if is_zero(p) {
+        return p
+    }
+    L := (3 * p.x * p.x) / (2 * p.y)
+    x := L*L - 2*p.x
+    return pt{
+        x: x,
+        y: L*(p.x-x) - p.y,
+    }
+}
+
+func add(p, q pt) pt {
+    if p.x == q.x && p.y == q.y {
+        return dbl(p)
+    }
+    if is_zero(p) {
+        return q
+    }
+    if is_zero(q) {
+        return p
+    }
+    L := (q.y - p.y) / (q.x - p.x)
+    x := L*L - p.x - q.x
+    return pt{
+        x: x,
+        y: L*(p.x-x) - p.y,
+    }
+}
+
+func mul(p pt, n int) pt {
+    r := zero()
+    for i := 1; i <= n; i <<= 1 {
+        if i&n != 0 {
+            r = add(r, p)
+        }
+        p = dbl(p)
+    }
+    return r
+}
+
+func show(s string, p pt) {
+    fmt.Printf("%s", s)
+    if is_zero(p) {
+        fmt.Println("Zero")
+    } else {
+        fmt.Printf("(%.3f, %.3f)\n", p.x, p.y)
+    }
+}
+
+func from_y(y float64) pt {
+    return pt{
+        x: math.Cbrt(y*y - bCoeff),
+        y: y,
+    }
+}
+
+func main() {
+    a := from_y(1)
+    b := from_y(2)
+    show("a = ", a)
+    show("b = ", b)
+    c := add(a, b)
+    show("c = a + b = ", c)
+    d := neg(c)
+    show("d = -c = ", d)
+    show("c + d = ", add(c, d))
+    show("a + b + d = ", add(a, add(b, d)))
+    show("a * 12345 = ", mul(a, 12345))
+}