Add optimized _OneByteString.toLowerCase.

sdk/lib/io/http_parser.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 // Global constants.
 class _Const {
   // Bytes for "HTTP".
   static const HTTP = const [72, 84, 84, 80];
@@ skipping 529 matching lines @@
           }
           _state = _State.HEADER_START;
           break;
 
         case _State.HEADER_START:
           _headers = new _HttpHeaders(version);
           if (byte == _CharCode.CR) {
             _state = _State.HEADER_ENDING;
           } else {
             // Start of new header field.
-            _headerField.add(_toLowerCase(byte));
+            _headerField.add(_toLowerCaseByte(byte));
             _state = _State.HEADER_FIELD;
           }
           break;
 
         case _State.HEADER_FIELD:
           if (byte == _CharCode.COLON) {
             _state = _State.HEADER_VALUE_START;
           } else {
             if (!_isTokenChar(byte)) {
               throw new HttpException("Invalid header field name");
             }
-            _headerField.add(_toLowerCase(byte));
+            _headerField.add(_toLowerCaseByte(byte));
           }
           break;
 
         case _State.HEADER_VALUE_START:
           if (byte == _CharCode.CR) {
             _state = _State.HEADER_VALUE_FOLDING_OR_ENDING;
           } else if (byte != _CharCode.SP && byte != _CharCode.HT) {
             // Start of new header value.
             _headerValue.add(byte);
             _state = _State.HEADER_VALUE;
@@ skipping 35 matching lines @@
             } else {
               _headers._add(headerField, headerValue);
             }
             _headerField.clear();
             _headerValue.clear();
 
             if (byte == _CharCode.CR) {
               _state = _State.HEADER_ENDING;
             } else {
               // Start of new header field.
-              _headerField.add(_toLowerCase(byte));
+              _headerField.add(_toLowerCaseByte(byte));
               _state = _State.HEADER_FIELD;
             }
           }
           break;
 
         case _State.HEADER_ENDING:
           _expect(byte, _CharCode.LF);
           _headers._mutable = false;
 
           _transferLength = _headers.contentLength;
@@ skipping 297 matching lines @@
         start = index + 1;
       } else if (headerValue[index] == " " || headerValue[index] == "\t") {
         start++;
       }
       index++;
     }
     tokens.add(headerValue.substring(start, index));
     return tokens;
   }
 
-  int _toLowerCase(int byte) {
-    final int aCode = "A".codeUnitAt(0);
-    final int zCode = "Z".codeUnitAt(0);
-    final int delta = "a".codeUnitAt(0) - aCode;
-    return (aCode <= byte && byte <= zCode) ? byte + delta : byte;
+  static int _toLowerCaseByte(int x) {
+    // Optimized version:
+    //  -  0x41 is 'A'
+    //  -  0x7f is ASCII mask
+    //  -  26 is the number of alpha characters.
+    //  -  0x20 is the delta between lower and upper chars.
+    return (((x - 0x41) & 0x7f) < 26) ? (x | 0x20) : x;
   }
 
   // expected should already be lowercase.
   bool _caseInsensitiveCompare(List<int> expected, List<int> value) {
     if (expected.length != value.length) return false;
     for (int i = 0; i < expected.length; i++) {
-      if (expected[i] != _toLowerCase(value[i])) return false;
+      if (expected[i] != _toLowerCaseByte(value[i])) return false;
     }
     return true;
   }
 
   int _expect(int val1, int val2) {
     if (val1 != val2) {
       throw new HttpException("Failed to parse HTTP");
     }
   }
 
@@ skipping 74 matching lines @@
     }
   }
 
   void _reportError(error, [stackTrace]) {
     if (_socketSubscription != null) _socketSubscription.cancel();
     _state = _State.FAILURE;
     _controller.addError(error, stackTrace);
     _controller.close();
   }
 }