More efficient _OneByteString.toLowerCase().

runtime/lib/string_patch.dart

Index: runtime/lib/string_patch.dart
diff --git a/runtime/lib/string_patch.dart b/runtime/lib/string_patch.dart
index 667a08772516cf18f3c5b8f8886ceddcd538fa33..0918af86a6aac71f83376dd4092fca57f84b4391 100644
--- a/runtime/lib/string_patch.dart
+++ b/runtime/lib/string_patch.dart
@@ -778,6 +778,61 @@ class _OneByteString extends _StringBase implements String {
     return result;
   }
 
+  // Lower-case conversion table for Latin-1.
+  static const _LC_TABLE = const [
+    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+    0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+    0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+    0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
+    0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
+    0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
+    0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
+    0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
+    0x40, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
+    0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+    0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
+    0x78, 0x79, 0x7a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f,
+    0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
+    0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+    0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
+    0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
+    0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
+    0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
+    0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
+    0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
+    0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
+    0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
+    0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
+    0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
+    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, 0xff,

[Lasse Reichstein Nielsen, 2014/03/25 16:35:37]

ff -> df

+    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 toLowerCase() {
+    upperCaseDetected: {

[srdjan, 2014/03/25 17:33:16]

Using label and breaks here looks gross, IMO. Why not use a separate function
instead: 'isAllLowerCase' or similar.

[Lasse Reichstein Nielsen, 2014/03/25 19:04:27]

Just me microoptimizing. 
On the test I used, it gave another few procent of improvement to do it this way
instead of calling a "_toLowerCaseConvert()" function.

+      for (int i = 0; i < this.length; i++) {
+        int c = this.codeUnitAt(i);
+        // Ranges: 0x41-0x5a ('A' - 'Z'), 0xc0-0xd6, 0xd8-0xde.
+        if (c != _LC_TABLE[c]) {
+          break upperCaseDetected;
+        }
+      }
+      return this;
+    }
+    // String contains upper case characters. Create a new string.
+    var result = _allocate(this.length);
+    for (int i = 0; i < this.length; i++) {
+      result._setAt(i, _LC_TABLE[this.codeUnitAt(i)]);
+    }
+    return result;

[sra1, 2014/03/25 19:07:14]

Are single character strings canonicalized (like in V8)?
If so,
   if (this.length == 1) return result[0];

I can't tell if line 233 is for canonicalization or due to a belief that using
substring with length 1 is common.

+  }
+
   // Allocates a string of given length, expecting its content to be
   // set using _setAt.
   static _OneByteString _allocate(int length) native "OneByteString_allocate";