Speedup stringsearch for two byte strings

test/mjsunit/string-indexof-1.js

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 59 matching lines @@
 assertEquals(1, twoByteString.indexOf("\u0391\u03a3"), "Alpha Sigma");
 assertEquals(2, twoByteString.indexOf("\u03a3\u03a3"), "Sigma Sigma");
 assertEquals(3, twoByteString.indexOf("\u03a3\u0395"), "Sigma Epsilon");
 
 assertEquals(-1, twoByteString.indexOf("\u0391\u03a3\u0395"),
     "Not Alpha Sigma Epsilon");
 
 //single char pattern
 assertEquals(4, twoByteString.indexOf("\u0395"));
 
+// test string with alignment traps
+var alignmentString = "\u1122\u2211\u2222\uFF00\u00FF\u00FF";
+assertEquals(2, alignmentString.indexOf("\u2222"));
+assertEquals(4, alignmentString.indexOf("\u00FF\u00FF"));
+
+var longAlignmentString = "\uFF00" + "\u00FF".repeat(10);
+assertEquals(1,
+    longAlignmentString.indexOf("\u00FF".repeat(10)));
+
 // Test complex string indexOf algorithms. Only trigger for long strings.
 
 // Long string that isn't a simple repeat of a shorter string.
 var long = "A";
 for(var i = 66; i < 76; i++) {  // from 'B' to 'K'
   long =  long + String.fromCharCode(i) + long;
 }
 
 // pattern of 15 chars, repeated every 16 chars in long
 var pattern = "ABACABADABACABA";
@@ skipping 26 matching lines @@
 var lengths = [1, 4, 15];  // Single char, simple and complex.
 var indices = [0x5, 0x65, 0x85, 0x105, 0x205, 0x285, 0x2005, 0x2085, 0xfff0];
 for (var lengthIndex = 0; lengthIndex < lengths.length; lengthIndex++) {
   var length = lengths[lengthIndex];
   for (var i = 0; i < indices.length; i++) {
     var index = indices[i];
     var pattern = allCharsString.substring(index, index + length);
     assertEquals(index, allCharsString.indexOf(pattern));
   }
 }