Avoid unnecessary copying when parsing doubles.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 3893ccb6ef22ee4ca4c9cae0313d870536245a70..bfb2bee526da27b765743d34ee1e8aa6277bf191 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -16907,6 +16907,35 @@ RawString* String::ToLowerCase(const String& str, Heap::Space space) {
   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.