Optimize algorithm for String.prototype.repeat(), fix value caching in others

src/harmony-string.js

Index: src/harmony-string.js
diff --git a/src/harmony-string.js b/src/harmony-string.js
index ae13745cdbf55989ad78b288843396ee5fab36e9..5aa1975340c2bf6ae97f930191e27a7677167336 100644
--- a/src/harmony-string.js
+++ b/src/harmony-string.js
@@ -21,12 +21,26 @@ function StringRepeat(count) {
     throw MakeRangeError("invalid_count_value", []);
   }
 
-  var elements = new InternalArray(n);
-  for (var i = 0; i < n; i++) {
-    elements[i] = s;
+  // O(log n) algorithm
+
+  if (n < 1) return "";
+
+  var res = "";
+
+  while (n > 1) {
+      if (n % 2) res += s;

[Yang, 2014/08/19 12:29:00]

two-character indent please.

+      n /= 2;
+      s += s;
   }
 
-  return %StringBuilderConcat(elements, n, "");
+  // unroll last iteration, no need to double the initial string again at the

[Yang, 2014/08/19 12:29:00]

Capitalize "unroll".

+  // final iteration.
+
+  // This flattens the string. It is a small overhead to significantly improve
+  // string handling
+  var array = new InternalArray(1);
+  array[0] = res + s;
+  return %StringBuilderConcat(array, 1, "");

[Yang, 2014/08/19 12:29:00]

Use %FlattenString

 }
 
 
@@ -81,8 +95,7 @@ function StringEndsWith(searchString /* position */) {  // length == 1
   }
 
   var end = MathMin(MathMax(pos, 0), s_len);
-  var ss_len = ss.length;
-  var start = end - ss_len;
+  var start = end - ss.length;
   if (start < 0) {
     return false;
   }
@@ -111,8 +124,7 @@ function StringContains(searchString /* position */) {  // length == 1
 
   var s_len = s.length;
   var start = MathMin(MathMax(pos, 0), s_len);
-  var ss_len = ss.length;
-  if (ss_len + start > s_len) {
+  if (ss.length + start > s_len) {
     return false;
   }