Simplify and optimize String::format.

third_party/WebKit/Source/wtf/text/WTFString.cpp

 /*
  * (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2010, 2012 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2007-2009 Torch Mobile, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #include "wtf/text/WTFString.h"
 
+#include "base/strings/string_util.h"
 #include "wtf/ASCIICType.h"
 #include "wtf/DataLog.h"
 #include "wtf/HexNumber.h"
 #include "wtf/MathExtras.h"
 #include "wtf/StringExtras.h"
 #include "wtf/Vector.h"
 #include "wtf/dtoa.h"
 #include "wtf/text/CString.h"
 #include "wtf/text/CharacterNames.h"
 #include "wtf/text/IntegerToStringConversion.h"
@@ skipping 274 matching lines @@
 }
 
 String String::foldCase() const {
   if (!m_impl)
     return String();
   return m_impl->foldCase();
 }
 
 String String::format(const char* format, ...) {
   va_list args;
+
+  // TODO(esprehn): base uses 1024, maybe we should use a bigger size too.
+  static const unsigned kDefaultSize = 256;
+  Vector<char, kDefaultSize> buffer(kDefaultSize);
+
   va_start(args, format);
-
-// Do the format once to get the length.
-#if COMPILER(MSVC)
-  int result = _vscprintf(format, args);
-#else
-  char ch;
-  int result = vsnprintf(&ch, 1, format, args);
-// We need to call va_end() and then va_start() again here, as the
-// contents of args is undefined after the call to vsnprintf
-// according to http://man.cx/snprintf(3)
-//
-// Not calling va_end/va_start here happens to work on lots of
-// systems, but fails e.g. on 64bit Linux.
-#endif
+  int length = base::vsnprintf(buffer.data(), buffer.size(), format, args);
   va_end(args);
 
-  if (result == 0)
-    return String("");
-  if (result < 0)
+  // TODO(esprehn): This can only happen if there's an encoding error, what's
+  // the locale set to inside blink? Can this happen? We should probably CHECK
+  // instead.
+  if (length < 0)
     return String();
 
-  Vector<char, 256> buffer;
-  unsigned len = result;
-  buffer.grow(len + 1);
+  if (static_cast<unsigned>(length) >= buffer.size()) {
+    // vsnprintf doesn't include the NUL terminator in the length so we need to
+    // add space for it when growing.
+    buffer.grow(length + 1);
 
-  va_start(args, format);
-  // Now do the formatting again, guaranteed to fit.
-  vsnprintf(buffer.data(), buffer.size(), format, args);
+    // We need to call va_end() and then va_start() each time we use args, as
+    // the contents of args is undefined after the call to vsnprintf according
+    // to http://man.cx/snprintf(3)
+    //
+    // Not calling va_end/va_start here happens to work on lots of systems, but
+    // fails e.g. on 64bit Linux.
+    va_start(args, format);
+    length = base::vsnprintf(buffer.data(), buffer.size(), format, args);
+    va_end(args);
+  }
 
-  va_end(args);
-
-  return StringImpl::create(reinterpret_cast<const LChar*>(buffer.data()), len);
+  CHECK_LT(static_cast<unsigned>(length), buffer.size());
+  return String(reinterpret_cast<const LChar*>(buffer.data()), length);
 }
 
 template <typename IntegerType>
 static String integerToString(IntegerType input) {
   IntegerToStringConverter<IntegerType> converter(input);
   return StringImpl::create(converter.characters8(), converter.length());
 }
 
 String String::number(int number) {
   return integerToString(number);
@@ skipping 484 matching lines @@
   }
   buffer.append('\0');
   return buffer;
 }
 
 Vector<char> asciiDebug(String& string) {
   return asciiDebug(string.impl());
 }
 
 #endif