Update getNAF

lib/util.js

@@ -27,14 +27,33 @@ exports.getNAF = function (num, w) {
   var naf = []
   var ws = 1 << w
   var ws2m1 = (ws << 1) - 1
-  for (var k = num.clone(); k.cmpn(0) === 1; k.iushrn(1)) {
-    var z = 0
-    if (k.isOdd()) {
-      var mod = k.andln(ws2m1)
-      z = (mod >= ws) ? (ws - mod) : mod
-      k.isubn(z)
+
+  var k = num.clone()
+  while (!k.isZero()) {
+    var i = 0
+    for (var d = 1; (k.words[0] & d) === 0 && i < 26; ++i, d <<= 1) {
+      naf.push(0)
+    }
+
+    if (i !== 0) {
+      k.iushrn(i)
+    } else {
+      var mod = k.words[0] & ws2m1
+      if (mod >= ws) {
+        naf.push(ws - mod)
+        k.isubn(ws - mod).iushrn(1)
+      } else {
+        k.words[0] -= mod
+        naf.push(mod)
+        if (!k.isZero()) {
+          for (i = w - 1; i > 0; --i) {
+            naf.push(0)
+          }
+
+          k.iushrn(w)
+        }
+      }
     }
-    naf.push(z)
   }
 
   return naf