Avoid UTF-8 decoding in num.toString.

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 15940 matching lines @@
 
 RawDouble* Double::NewCanonical(const String& str) {
   double double_value;
   if (!CStringToDouble(str.ToCString(), str.Length(), &double_value)) {
     return Double::Handle().raw();
   }
   return NewCanonical(double_value);
 }
 
 
+RawString* Number::ToString(Heap::Space space) const {
+  // Refactoring can avoid Zone::Alloc and strlen, but gains are insignificant.
+  const char* cstr = ToCString();
+  intptr_t len = strlen(cstr);
+  // Resulting string is ASCII ...
+#ifdef DEBUG
+  for (intptr_t i = 0; i < len; ++i) {
+    ASSERT(static_cast<uint8_t>(cstr[i]) < 128);
+  }
+#endif  // DEBUG
+  // ... which is a subset of Latin-1.
+  return String::FromLatin1(reinterpret_cast<const uint8_t*>(cstr), len, space);
+}
+
+
 const char* Double::ToCString() const {
   if (isnan(value())) {
     return "NaN";
   }
   if (isinf(value())) {
     return value() < 0 ? "-Infinity" : "Infinity";
   }
   const int kBufferSize = 128;
   char* buffer = Isolate::Current()->current_zone()->Alloc<char>(kBufferSize);
   buffer[kBufferSize - 1] = '\0';
@@ skipping 3512 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart