Narrow String::CharAt from int32_t to uint16_t.

runtime/vm/object.cc

 // 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.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 17055 matching lines @@
   }
   return hasher.Finalize(String::kHashBits);
 }
 
 
 intptr_t String::Hash(const int32_t* characters, intptr_t len) {
   return HashImpl(characters, len);
 }
 
 
-int32_t String::CharAt(intptr_t index) const {
+uint16_t String::CharAt(intptr_t index) const {
   intptr_t class_id = raw()->GetClassId();
   ASSERT(RawObject::IsStringClassId(class_id));
   NoGCScope no_gc;
   if (class_id == kOneByteStringCid) {
     return *OneByteString::CharAddr(*this, index);
   }
   if (class_id == kTwoByteStringCid) {
     return *TwoByteString::CharAddr(*this, index);
   }
   if (class_id == kExternalOneByteStringCid) {
@@ skipping 136 matching lines @@
     str1.Equals(*this, 0, str1.Length()) &&
     str2.Equals(*this, str1.Length(), str2.Length());
 }
 
 
 intptr_t String::CompareTo(const String& other) const {
   const intptr_t this_len = this->Length();
   const intptr_t other_len = other.IsNull() ? 0 : other.Length();
   const intptr_t len = (this_len < other_len) ? this_len : other_len;
   for (intptr_t i = 0; i < len; i++) {
-    int32_t this_code_point = this->CharAt(i);
-    int32_t other_code_point = other.CharAt(i);
-    if (this_code_point < other_code_point) {
+    uint16_t this_code_unit = this->CharAt(i);
+    uint16_t other_code_unit = other.CharAt(i);
+    if (this_code_unit < other_code_unit) {
       return -1;
     }
-    if (this_code_point > other_code_point) {
+    if (this_code_unit > other_code_unit) {
       return 1;
     }
   }
   if (this_len < other_len) return -1;
   if (this_len > other_len) return 1;
   return 0;
 }
 
 
 bool String::StartsWith(const String& other) const {
@@ skipping 3103 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart