Make smi.toString() do its work faster using native string helpers.

runtime/lib/integers.dart

Index: runtime/lib/integers.dart
diff --git a/runtime/lib/integers.dart b/runtime/lib/integers.dart
index 7c242ef95659a9872e9810492060f0d695f8dc13..aa2267efc0a9be8ad733fc28ff7e569242e77d53 100644
--- a/runtime/lib/integers.dart
+++ b/runtime/lib/integers.dart
@@ -233,31 +233,38 @@ class _Smi extends _IntegerImplementation implements int {
 
   String toString() {
     if (this == 0) return "0";
-    var reversed = new List();
-    var val = this < 0 ? -this : this;
+    var reversed = _toStringBuffer;
+    var negative = false;
+    var val = this;
+    int index = 0;
+
+    if (this < 0) {

[kasperl, 2013/09/24 11:22:09]

Use val < 0?

[Lasse Reichstein Nielsen, 2013/09/24 19:48:49]

good point.

+      negative = true;
+      // Handle the first digit as negative to avoid negating the minimum
+      // smi, for which the negation is not a smi.
+      int digit = -(val.remainder(10));
+      reversed[index++] = digit + 0x30;
+      val = -(val ~/ 10);
+    }
+
     while (val > 0) {
-      reversed.add((val % 10) + 0x30);
+      int digit = val % 10;
+      reversed[index++] = (digit + 0x30);
       val = val ~/ 10;
     }
-    final int numDigits = reversed.length;
-    List digits;
-    int i;
-    if (this < 0) {
-      digits = new List(numDigits + 1);
-      digits[0] = 0x2D;  // '-'.
-      i = 1;
-    } else {
-      digits = new List(numDigits);
-      i = 0;
-    }
-    int ri = reversed.length - 1;
-    for (; i < digits.length; i++, ri--) {
-      digits[i] = reversed[ri];
+    if (negative) reversed[index++] = 0x2D;  // '-'.
+
+    _OneByteString string = _OneByteString._allocate(index);
+    for (int i = 0, j = index; i < index; i++) {
+      string._setAt(i, reversed[--j]);
     }
-    return _StringBase.createFromCharCodes(digits);
+    return string;
   }
 }
 
+// Reusable buffer used by smi.toString.
+List _toStringBuffer = new Uint8List(20);
+
 // Represents integers that cannot be represented by Smi but fit into 64bits.
 class _Mint extends _IntegerImplementation implements int {
   factory _Mint._uninstantiable() {