Port and integrate the irregexp engine from V8

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,
                                            [int start = 0, int end]) {
     return _StringBase.createFromCharCodes(charCodes, start, end);
   }
 
@@ skipping 721 matching lines @@
       native "OneByteString_splitWithCharCode";
 
   List<String> split(Pattern pattern) {
     if ((ClassID.getID(pattern) == ClassID.cidOneByteString) &&
         (pattern.length == 1)) {
       return _splitWithCharCode(pattern.codeUnitAt(0));
     }
     return super.split(pattern);
   }
 
+  // The codeUnitsAt family of functions is inlined to an unchecked
+  // LoadCodeUnitsInstr, therefore `this` must be a valid string, and `index`
+  // must be in bounds.
+  int _oneCodeUnitAt(int index) => _codeUnitsAt(index, 1);
+  int _twoCodeUnitsAt(int index) => _codeUnitsAt(index, 2);
+  int _fourCodeUnitsAt(int index) => _codeUnitsAt(index, 4);
+
+  // Loads up to 4 code units into a single integer.
+  int _codeUnitsAt(int index, int count) {
+    assert(index >= 0);
+    assert(index + count - 1 < this.length);
+    assert(0 < count && count <= 4);
+
+    int codeUnits = 0;
+    for (int i = 0; i < count; i++) {
+      codeUnits |= this.codeUnitAt(index + i) << (i * 8);
+    }
+
+    return codeUnits;
+  }
+
   // All element of 'strings' must be OneByteStrings.
   static _concatAll(List<String> strings, int totalLength) {
     // TODO(srdjan): Improve code below and raise or eliminate the limit.
     if (totalLength > 128) {
       // Native is quicker.
       return _StringBase._concatRangeNative(strings, 0, strings.length);
     }
     final res = _OneByteString._allocate(totalLength);
     final stringsLength = strings.length;
     int rIx = 0;
@@ skipping 244 matching lines @@
         "_TwoByteString can only be allocated by the VM");
   }
 
   bool _isWhitespace(int codeUnit) {
     return _StringBase._isTwoByteWhitespace(codeUnit);
   }
 
   bool operator ==(Object other) {
     return super == other;
   }
+
+  int _oneCodeUnitAt(int index) => _codeUnitsAt(index, 1);
+  int _twoCodeUnitsAt(int index) => _codeUnitsAt(index, 2);
+
+  // Loads up to 2 code units into a single integer.
+  int _codeUnitsAt(int index, int count) {
+    assert(index >= 0);
+    assert(index + count - 1 < this.length);
+    assert(0 < count && count <= 2);
+
+    int codeUnits = 0;
+    for (int i = 0; i < count; i++) {
+      codeUnits |= this.codeUnitAt(index + i) << (i * 16);
+    }
+
+    return codeUnits;
+  }
 }
 
 
 class _ExternalOneByteString extends _StringBase implements String {
   factory _ExternalOneByteString._uninstantiable() {
     throw new UnsupportedError(
         "_ExternalOneByteString can only be allocated by the VM");
   }
 
   bool _isWhitespace(int codeUnit) {
@@ skipping 59 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);
 }