Improve performance of String::ToCString for OneByteString and parsing of doubles. Leads to signifi…

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/bigint_operations.h"
@@ skipping 10709 matching lines @@
 intptr_t String::Hash(const int32_t* characters, intptr_t len) {
   return HashImpl(characters, len);
 }
 
 
 int32_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);
+    return *OneByteString::CharAddr(*this, index);
   }
   if (class_id == kTwoByteStringCid) {
-      return *TwoByteString::CharAddr(*this, index);
+    return *TwoByteString::CharAddr(*this, index);
   }
   if (class_id == kExternalOneByteStringCid) {
-      return *ExternalOneByteString::CharAddr(*this, index);
+    return *ExternalOneByteString::CharAddr(*this, index);
   }
   ASSERT(class_id == kExternalTwoByteStringCid);
   return *ExternalTwoByteString::CharAddr(*this, index);
 }
 
 
 intptr_t String::CharSize() const {
   intptr_t class_id = raw()->GetClassId();
   if (class_id == kOneByteStringCid || class_id == kExternalOneByteStringCid) {
     return kOneByteChar;
@@ skipping 452 matching lines @@
     result = OneByteString::New(length, space);
   } else {
     result = TwoByteString::New(length, space);
   }
   String::Copy(result, 0, str, begin_index, length);
   return result.raw();
 }
 
 
 const char* String::ToCString() const {
-  intptr_t len = Utf8::Length(*this);
+  if (IsOneByteString()) {
+    // Quick conversion if OneByteString contains only ASCII characters.
+    intptr_t len = Length();
+    if (len == 0) {
+      return "";
+    }
+    Zone* zone = Isolate::Current()->current_zone();
+    uint8_t* result = zone->Alloc<uint8_t>(len + 1);
+    NoGCScope no_gc;
+    const uint8_t* original_str = OneByteString::CharAddr(*this, 0);
+    for (intptr_t i = 0; i < len; i++) {
+      if (original_str[i] <= Utf8::kMaxOneByteChar) {
+        result[i] = original_str[i];
+      } else {
+        len = -1;
+        break;
+      }
+    }
+    if (len > 0) {
+      result[len] = 0;
+      return reinterpret_cast<const char*>(result);
+    }
+  }
+  const intptr_t len = Utf8::Length(*this);
   Zone* zone = Isolate::Current()->current_zone();
   uint8_t* result = zone->Alloc<uint8_t>(len + 1);
   ToUTF8(result, len);
   result[len] = 0;
   return reinterpret_cast<const char*>(result);
 }
 
 
 void String::ToUTF8(uint8_t* utf8_array, intptr_t array_len) const {
   ASSERT(array_len >= Utf8::Length(*this));
@@ skipping 1772 matching lines @@
   }
   return result.raw();
 }
 
 
 const char* WeakProperty::ToCString() const {
   return "_WeakProperty";
 }
 
 }  // namespace dart