Speed up toLowerCase, by manually inlining the upper-case part.

runtime/lib/string_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 patch class String {
   /* patch */ factory String.fromCharCodes(Iterable<int> charCodes) {
     return _StringBase.createFromCharCodes(charCodes);
   }
 
   /* patch */ const factory String.fromEnvironment(String name,
@@ skipping 796 matching lines @@
     0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
     0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
     0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xd7,
     0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xdf,
     0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
     0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
     0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
     0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
   ];
 
-  String _toLowerCaseUpperCaseDetectedAt(int firstUpperCaseIndex) {
-    // String contains upper case characters. Create a new string.
-    final length = this.length;
-    final result = _allocate(length);
-    // First up to firstUpperIndex.
-    int i = 0;
-    for (; i < firstUpperCaseIndex; i++) {
-      result._setAt(i, this.codeUnitAt(i));
-    }
-    for (; i < length; i++) {
-      result._setAt(i, _LC_TABLE[this.codeUnitAt(i)]);
-    }
-    return result;
-  }
-
   String toLowerCase() {
     for (int i = 0; i < this.length; i++) {
       final c = this.codeUnitAt(i);
-      // Ranges: 0x41-0x5a ('A' - 'Z'), 0xc0-0xd6, 0xd8-0xde.
-      if (c != _LC_TABLE[c]) {
-        return _toLowerCaseUpperCaseDetectedAt(i);
+      if (c == _LC_TABLE[c]) continue;
+      // Upper-case character found.
+      final result = _allocate(this.length);
+      for (int j = 0; j < i; j++) {
+        result._setAt(j, this.codeUnitAt(j));
       }
+      for (int j = i; j < this.length; j++) {
+        // Ranges: 0x41-0x5a ('A' - 'Z'), 0xc0-0xd6, 0xd8-0xde.

[Lasse Reichstein Nielsen, 2014/03/26 11:37:51]

Maybe move this comment to the table?
// Upper-case ranges are: ....
// Conversion to lower case performed by adding 0x20.

[Anders Johnsen, 2014/03/26 11:39:12]

Done.

+        result._setAt(j, _LC_TABLE[this.codeUnitAt(j)]);
+      }
+      return result;
     }
     return this;
   }
 
   // Allocates a string of given length, expecting its content to be
   // set using _setAt.
   static _OneByteString _allocate(int length) native "OneByteString_allocate";
 
 
   static _OneByteString _allocateFromOneByteList(List<int> list)
@@ skipping 94 matching lines @@
 class _CodeUnits extends Object with ListMixin<int>,
                                      UnmodifiableListMixin<int> {
   /** The string that this is the code units of. */
   String _string;
 
   _CodeUnits(this._string);
 
   int get length => _string.length;
   int operator[](int i) => _string.codeUnitAt(i);
 }