[builtins] Migrate String.prototype.trim/trimLeft/trimRight to C++.

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 9964 matching lines @@
   if (IsEmpty()) return other->IsEmpty();
   if (other->IsEmpty()) return false;
   if (length() != other->length()) return false;
   for (int i = 0; i < length(); ++i) {
     if (get(i) != other->get(i)) return false;
   }
   return true;
 }
 #endif
 
+// static
+Handle<String> String::Trim(Handle<String> string, TrimMode mode) {
+  Isolate* const isolate = string->GetIsolate();
+
+  // Flatten the input {string}.

[Franzi, 2016/05/27 14:20:08]

Do we need this comment?

[Benedikt Meurer, 2016/05/27 17:20:58]

Done.

+  string = String::Flatten(string);
+  int const length = string->length();
+
+  // Perform left trimming if requested.
+  int left = 0;
+  UnicodeCache* unicode_cache = isolate->unicode_cache();
+  if (mode & kTrimLeft) {

[Franzi, 2016/05/27 14:20:08]

For readability, I would prefer

if (mode == kTrimLeft || mode == kTrim) {...}

Expecting a certain relationship between the values seems unnecessary to me.
Then we don't need the initializers in the enum declaration. 
enum TrimMode {
  kTrimLeft,
  kTrimRight,
  kTrim
};

[Benedikt Meurer, 2016/05/27 17:20:58]

Good suggestion, thanks. Did that.

+    while (left < length &&
+           unicode_cache->IsWhiteSpaceOrLineTerminator(string->Get(left))) {
+      left++;
+    }
+  }
+
+  // Perform right trimming if requested.
+  int right = length;
+  if (mode & kTrimRight) {
+    while (
+        right > left &&
+        unicode_cache->IsWhiteSpaceOrLineTerminator(string->Get(right - 1))) {
+      right--;
+    }
+  }
+
+  return isolate->factory()->NewSubString(string, left, right);
+}
 
 bool String::LooksValid() {
   if (!GetIsolate()->heap()->Contains(this)) return false;
   return true;
 }
 
 
 // static
 MaybeHandle<String> Name::ToFunctionName(Handle<Name> name) {
   if (name->IsString()) return Handle<String>::cast(name);
@@ skipping 8530 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8