Avoid unnecessary copying when parsing doubles.

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 16889 matching lines @@
   // TODO(cshapiro): create a fast-path for OneByteString instances.
   return Transform(CaseMapping::ToUpper, str, space);
 }
 
 
 RawString* String::ToLowerCase(const String& str, Heap::Space space) {
   // TODO(cshapiro): create a fast-path for OneByteString instances.
   return Transform(CaseMapping::ToLower, str, space);
 }
 
+bool String::ParseDouble(const String& str,
+                         intptr_t start, intptr_t end,
+                         double* result) {
+  ASSERT(0 <= start);
+  ASSERT(start <= end);
+  ASSERT(end <= str.Length());
+  int length = end - start;

[Ivan Posva, 2014/07/03 19:44:14]

Please always use intptr_t.

[Lasse Reichstein Nielsen, 2014/07/04 06:46:01]

Ack, yes. Will do.

+  NoGCScope no_gc;
+  const uint8_t* startChar;
+  if (str.IsOneByteString()) {
+    startChar = OneByteString::CharAddr(str, start);
+  } else if (str.IsExternalOneByteString()) {
+    startChar = ExternalOneByteString::CharAddr(str, start);
+  } else {
+    uint8_t* chars = Isolate::Current()->current_zone()->Alloc<uint8_t>(length);
+    for (int i = 0; i < length; i++) {

[Ivan Posva, 2014/07/03 19:44:14]

intptr_t

+      int ch = str.CharAt(start + i);

[Ivan Posva, 2014/07/03 19:44:14]

The return type of CharAt is int32_t.

Also it would be better to get the CharAt function using CharAtFunc once outside
the loop to avoid the repeated virtual dispatch.

[Lasse Reichstein Nielsen, 2014/07/04 06:46:01]

Will do.
Didn't know about the CharAtFunc - nice!

+      if (ch < 128) {
+        chars[i] = ch;
+      } else {
+        return false;  // Not ASCII, so definitely not valid double numeral.
+      }
+    }
+    startChar = chars;
+  }
+  return CStringToDouble(reinterpret_cast<const char*>(startChar),
+                         length, result);
+}
+
 
 // Check to see if 'str1' matches 'str2' as is or
 // once the private key separator is stripped from str2.
 //
 // Things are made more complicated by the fact that constructors are
 // added *after* the private suffix, so "foo@123.named" should match
 // "foo.named".
 //
 // Also, the private suffix can occur more than once in the name, as in:
 //
@@ skipping 2072 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart