curves: optimize Maxwell's trick

indutny · indutny · commit e102a69665ae · 2016-06-14T00:44:33.000-04:00
diff --git a/lib/elliptic/curve/edwards.js b/lib/elliptic/curve/edwards.js
@@ -414,8 +414,13 @@ Point.prototype.eqXToP = function eqXToP(x) {
   if (this.x.cmp(rx) === 0)
     return true;
 
+  var xc = x.clone();
   var t = this.curve.redN.redMul(this.z);
   for (var i = 1; i <= this.curve._maxwellAdjust; i++) {
+    xc.iadd(this.curve.n);
+    if (xc.cmp(this.curve.p) >= 0)
+      return false;
+
     rx.redIAdd(t);
     if (this.x.cmp(rx) === 0)
       return true;
diff --git a/lib/elliptic/curve/short.js b/lib/elliptic/curve/short.js
@@ -910,8 +910,13 @@ JPoint.prototype.eqXToP = function eqXToP(x) {
   if (this.x.cmp(rx) === 0)
     return true;
 
+  var xc = x.clone();
   var t = this.curve.redN.redMul(zs);
   for (var i = 1; i <= this.curve._maxwellAdjust; i++) {
+    xc.iadd(this.curve.n);
+    if (xc.cmp(this.curve.p) >= 0)
+      return false;
+
     rx.redIAdd(t);
     if (this.x.cmp(rx) === 0)
       return true;
