src/string-builder.h - v8/v8.git - Git at Google

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #ifndef V8_STRING_BUILDER_H_
 #define V8_STRING_BUILDER_H_

 #include "src/assert-scope.h"
 #include "src/factory.h"
 #include "src/handles.h"
 #include "src/isolate.h"
 #include "src/objects.h"
 #include "src/utils.h"

 namespace v8 {
 namespace internal {

 const int kStringBuilderConcatHelperLengthBits = 11;
 const int kStringBuilderConcatHelperPositionBits = 19;

 typedef BitField<int, 0, kStringBuilderConcatHelperLengthBits>
     StringBuilderSubstringLength;
 typedef BitField<int, kStringBuilderConcatHelperLengthBits,
                  kStringBuilderConcatHelperPositionBits>
     StringBuilderSubstringPosition;


 template <typename sinkchar>
 static inline void StringBuilderConcatHelper(String* special, sinkchar* sink,
                                              FixedArray* fixed_array,
                                              int array_length) {
   DisallowHeapAllocation no_gc;
   int position = 0;
   for (int i = 0; i < array_length; i++) {
     Object* element = fixed_array->get(i);
     if (element->IsSmi()) {
       // Smi encoding of position and length.
       int encoded_slice = Smi::cast(element)->value();
       int pos;
       int len;
       if (encoded_slice > 0) {
         // Position and length encoded in one smi.
         pos = StringBuilderSubstringPosition::decode(encoded_slice);
         len = StringBuilderSubstringLength::decode(encoded_slice);
       } else {
         // Position and length encoded in two smis.
         Object* obj = fixed_array->get(++i);
         DCHECK(obj->IsSmi());
         pos = Smi::cast(obj)->value();
         len = -encoded_slice;
       }
       String::WriteToFlat(special, sink + position, pos, pos + len);
       position += len;
     } else {
       String* string = String::cast(element);
       int element_length = string->length();
       String::WriteToFlat(string, sink + position, 0, element_length);
       position += element_length;
     }
   }
 }


 // Returns the result length of the concatenation.
 // On illegal argument, -1 is returned.
 static inline int StringBuilderConcatLength(int special_length,
                                             FixedArray* fixed_array,
                                             int array_length, bool* one_byte) {
   DisallowHeapAllocation no_gc;
   int position = 0;
   for (int i = 0; i < array_length; i++) {
     int increment = 0;
     Object* elt = fixed_array->get(i);
     if (elt->IsSmi()) {
       // Smi encoding of position and length.
       int smi_value = Smi::cast(elt)->value();
       int pos;
       int len;
       if (smi_value > 0) {
         // Position and length encoded in one smi.
         pos = StringBuilderSubstringPosition::decode(smi_value);
         len = StringBuilderSubstringLength::decode(smi_value);
       } else {
         // Position and length encoded in two smis.
         len = -smi_value;
         // Get the position and check that it is a positive smi.
         i++;
         if (i >= array_length) return -1;
         Object* next_smi = fixed_array->get(i);
         if (!next_smi->IsSmi()) return -1;
         pos = Smi::cast(next_smi)->value();
         if (pos < 0) return -1;
       }
       DCHECK(pos >= 0);
       DCHECK(len >= 0);
       if (pos > special_length || len > special_length - pos) return -1;
       increment = len;
     } else if (elt->IsString()) {
       String* element = String::cast(elt);
       int element_length = element->length();
       increment = element_length;
       if (*one_byte && !element->HasOnlyOneByteChars()) {
         *one_byte = false;
       }
     } else {
       return -1;
     }
     if (increment > String::kMaxLength - position) {
       return kMaxInt;  // Provoke throw on allocation.
     }
     position += increment;
   }
   return position;
 }


 class FixedArrayBuilder {
  public:
   explicit FixedArrayBuilder(Isolate* isolate, int initial_capacity)
       : array_(isolate->factory()->NewFixedArrayWithHoles(initial_capacity)),
         length_(0),
         has_non_smi_elements_(false) {
     // Require a non-zero initial size. Ensures that doubling the size to
     // extend the array will work.
     DCHECK(initial_capacity > 0);
   }

   explicit FixedArrayBuilder(Handle<FixedArray> backing_store)
       : array_(backing_store), length_(0), has_non_smi_elements_(false) {
     // Require a non-zero initial size. Ensures that doubling the size to
     // extend the array will work.
     DCHECK(backing_store->length() > 0);
   }

   bool HasCapacity(int elements) {
     int length = array_->length();
     int required_length = length_ + elements;
     return (length >= required_length);
   }

   void EnsureCapacity(int elements) {
     int length = array_->length();
     int required_length = length_ + elements;
     if (length < required_length) {
       int new_length = length;
       do {
         new_length *= 2;
       } while (new_length < required_length);
       Handle<FixedArray> extended_array =
           array_->GetIsolate()->factory()->NewFixedArrayWithHoles(new_length);
       array_->CopyTo(0, *extended_array, 0, length_);
       array_ = extended_array;
     }
   }

   void Add(Object* value) {
     DCHECK(!value->IsSmi());
     DCHECK(length_ < capacity());
     array_->set(length_, value);
     length_++;
     has_non_smi_elements_ = true;
   }

   void Add(Smi* value) {
     DCHECK(value->IsSmi());
     DCHECK(length_ < capacity());
     array_->set(length_, value);
     length_++;
   }

   Handle<FixedArray> array() { return array_; }

   int length() { return length_; }

   int capacity() { return array_->length(); }

   Handle<JSArray> ToJSArray(Handle<JSArray> target_array) {
     JSArray::SetContent(target_array, array_);
     target_array->set_length(Smi::FromInt(length_));
     return target_array;
   }

  private:
   Handle<FixedArray> array_;
   int length_;
   bool has_non_smi_elements_;
 };


 class ReplacementStringBuilder {
  public:
   ReplacementStringBuilder(Heap* heap, Handle<String> subject,
                            int estimated_part_count)
       : heap_(heap),
         array_builder_(heap->isolate(), estimated_part_count),
         subject_(subject),
         character_count_(0),
         is_one_byte_(subject->IsOneByteRepresentation()) {
     // Require a non-zero initial size. Ensures that doubling the size to
     // extend the array will work.
     DCHECK(estimated_part_count > 0);
   }

   static inline void AddSubjectSlice(FixedArrayBuilder* builder, int from,
                                      int to) {
     DCHECK(from >= 0);
     int length = to - from;
     DCHECK(length > 0);
     if (StringBuilderSubstringLength::is_valid(length) &&
         StringBuilderSubstringPosition::is_valid(from)) {
       int encoded_slice = StringBuilderSubstringLength::encode(length) |
                           StringBuilderSubstringPosition::encode(from);
       builder->Add(Smi::FromInt(encoded_slice));
     } else {
       // Otherwise encode as two smis.
       builder->Add(Smi::FromInt(-length));
       builder->Add(Smi::FromInt(from));
     }
   }


   void EnsureCapacity(int elements) { array_builder_.EnsureCapacity(elements); }


   void AddSubjectSlice(int from, int to) {
     AddSubjectSlice(&array_builder_, from, to);
     IncrementCharacterCount(to - from);
   }


   void AddString(Handle<String> string) {
     int length = string->length();
     DCHECK(length > 0);
     AddElement(*string);
     if (!string->IsOneByteRepresentation()) {
       is_one_byte_ = false;
     }
     IncrementCharacterCount(length);
   }


   MaybeHandle<String> ToString();


   void IncrementCharacterCount(int by) {
     if (character_count_ > String::kMaxLength - by) {
       STATIC_ASSERT(String::kMaxLength < kMaxInt);
       character_count_ = kMaxInt;
     } else {
       character_count_ += by;
     }
   }

  private:
   void AddElement(Object* element) {
     DCHECK(element->IsSmi() || element->IsString());
     DCHECK(array_builder_.capacity() > array_builder_.length());
     array_builder_.Add(element);
   }

   Heap* heap_;
   FixedArrayBuilder array_builder_;
   Handle<String> subject_;
   int character_count_;
   bool is_one_byte_;
 };


 class IncrementalStringBuilder {
  public:
   explicit IncrementalStringBuilder(Isolate* isolate);

   INLINE(String::Encoding CurrentEncoding()) { return encoding_; }

   template <typename SrcChar, typename DestChar>
   INLINE(void Append(SrcChar c));

   INLINE(void AppendCharacter(uint8_t c)) {
     if (encoding_ == String::ONE_BYTE_ENCODING) {
       Append<uint8_t, uint8_t>(c);
     } else {
       Append<uint8_t, uc16>(c);
     }
   }

   INLINE(void AppendCString(const char* s)) {
     const uint8_t* u = reinterpret_cast<const uint8_t*>(s);
     if (encoding_ == String::ONE_BYTE_ENCODING) {
       while (*u != '\0') Append<uint8_t, uint8_t>(*(u++));
     } else {
       while (*u != '\0') Append<uint8_t, uc16>(*(u++));
     }
   }

   INLINE(void AppendCString(const uc16* s)) {
     if (encoding_ == String::ONE_BYTE_ENCODING) {
       while (*s != '\0') Append<uc16, uint8_t>(*(s++));
     } else {
       while (*s != '\0') Append<uc16, uc16>(*(s++));
     }
   }

   INLINE(bool CurrentPartCanFit(int length)) {
     return part_length_ - current_index_ > length;
   }

   void AppendString(Handle<String> string);

   MaybeHandle<String> Finish();

   INLINE(bool HasOverflowed()) const { return overflowed_; }

   // Change encoding to two-byte.
   void ChangeEncoding() {
     DCHECK_EQ(String::ONE_BYTE_ENCODING, encoding_);
     ShrinkCurrentPart();
     encoding_ = String::TWO_BYTE_ENCODING;
     Extend();
   }

   template <typename DestChar>
   class NoExtend {
    public:
     explicit NoExtend(Handle<String> string, int offset) {
       DCHECK(string->IsSeqOneByteString() || string->IsSeqTwoByteString());
       if (sizeof(DestChar) == 1) {
         start_ = reinterpret_cast<DestChar*>(
             Handle<SeqOneByteString>::cast(string)->GetChars() + offset);
       } else {
         start_ = reinterpret_cast<DestChar*>(
             Handle<SeqTwoByteString>::cast(string)->GetChars() + offset);
       }
       cursor_ = start_;
     }

     INLINE(void Append(DestChar c)) { *(cursor_++) = c; }
     INLINE(void AppendCString(const char* s)) {
       const uint8_t* u = reinterpret_cast<const uint8_t*>(s);
       while (*u != '\0') Append(*(u++));
     }

     int written() { return static_cast<int>(cursor_ - start_); }

    private:
     DestChar* start_;
     DestChar* cursor_;
     DisallowHeapAllocation no_gc_;
   };

   template <typename DestChar>
   class NoExtendString : public NoExtend<DestChar> {
    public:
     NoExtendString(Handle<String> string, int required_length)
         : NoExtend<DestChar>(string, 0), string_(string) {
       DCHECK(string->length() >= required_length);
     }

     Handle<String> Finalize() {
       Handle<SeqString> string = Handle<SeqString>::cast(string_);
       int length = NoExtend<DestChar>::written();
       Handle<String> result = SeqString::Truncate(string, length);
       string_ = Handle<String>();
       return result;
     }

    private:
     Handle<String> string_;
   };

   template <typename DestChar>
   class NoExtendBuilder : public NoExtend<DestChar> {
    public:
     NoExtendBuilder(IncrementalStringBuilder* builder, int required_length)
         : NoExtend<DestChar>(builder->current_part(), builder->current_index_),
           builder_(builder) {
       DCHECK(builder->CurrentPartCanFit(required_length));
     }

     ~NoExtendBuilder() {
       builder_->current_index_ += NoExtend<DestChar>::written();
     }

    private:
     IncrementalStringBuilder* builder_;
   };

  private:
   Factory* factory() { return isolate_->factory(); }

   INLINE(Handle<String> accumulator()) { return accumulator_; }

   INLINE(void set_accumulator(Handle<String> string)) {
     *accumulator_.location() = *string;
   }

   INLINE(Handle<String> current_part()) { return current_part_; }

   INLINE(void set_current_part(Handle<String> string)) {
     *current_part_.location() = *string;
   }

   // Add the current part to the accumulator.
   void Accumulate(Handle<String> new_part);

   // Finish the current part and allocate a new part.
   void Extend();

   // Shrink current part to the right size.
   void ShrinkCurrentPart() {
     DCHECK(current_index_ < part_length_);
     set_current_part(SeqString::Truncate(
         Handle<SeqString>::cast(current_part()), current_index_));
   }

   static const int kInitialPartLength = 32;
   static const int kMaxPartLength = 16 * 1024;
   static const int kPartLengthGrowthFactor = 2;

   Isolate* isolate_;
   String::Encoding encoding_;
   bool overflowed_;
   int part_length_;
   int current_index_;
   Handle<String> accumulator_;
   Handle<String> current_part_;
 };


 template <typename SrcChar, typename DestChar>
 void IncrementalStringBuilder::Append(SrcChar c) {
   DCHECK_EQ(encoding_ == String::ONE_BYTE_ENCODING, sizeof(DestChar) == 1);
   if (sizeof(DestChar) == 1) {
     DCHECK_EQ(String::ONE_BYTE_ENCODING, encoding_);
     SeqOneByteString::cast(*current_part_)
         ->SeqOneByteStringSet(current_index_++, c);
   } else {
     DCHECK_EQ(String::TWO_BYTE_ENCODING, encoding_);
     SeqTwoByteString::cast(*current_part_)
         ->SeqTwoByteStringSet(current_index_++, c);
   }
   if (current_index_ == part_length_) Extend();
 }
 }  // namespace internal
 }  // namespace v8

 #endif  // V8_STRING_BUILDER_H_
	// Copyright 2014 the V8 project authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#ifndef V8_STRING_BUILDER_H_
	#define V8_STRING_BUILDER_H_

	#include "src/assert-scope.h"
	#include "src/factory.h"
	#include "src/handles.h"
	#include "src/isolate.h"
	#include "src/objects.h"
	#include "src/utils.h"

	namespace v8 {
	namespace internal {

	const int kStringBuilderConcatHelperLengthBits = 11;
	const int kStringBuilderConcatHelperPositionBits = 19;

	typedef BitField<int, 0, kStringBuilderConcatHelperLengthBits>
	StringBuilderSubstringLength;
	typedef BitField<int, kStringBuilderConcatHelperLengthBits,
	kStringBuilderConcatHelperPositionBits>
	StringBuilderSubstringPosition;


	template <typename sinkchar>
	static inline void StringBuilderConcatHelper(String* special, sinkchar* sink,
	FixedArray* fixed_array,
	int array_length) {
	DisallowHeapAllocation no_gc;
	int position = 0;
	for (int i = 0; i < array_length; i++) {
	Object* element = fixed_array->get(i);
	if (element->IsSmi()) {
	// Smi encoding of position and length.
	int encoded_slice = Smi::cast(element)->value();
	int pos;
	int len;
	if (encoded_slice > 0) {
	// Position and length encoded in one smi.
	pos = StringBuilderSubstringPosition::decode(encoded_slice);
	len = StringBuilderSubstringLength::decode(encoded_slice);
	} else {
	// Position and length encoded in two smis.
	Object* obj = fixed_array->get(++i);
	DCHECK(obj->IsSmi());
	pos = Smi::cast(obj)->value();
	len = -encoded_slice;
	}
	String::WriteToFlat(special, sink + position, pos, pos + len);
	position += len;
	} else {
	String* string = String::cast(element);
	int element_length = string->length();
	String::WriteToFlat(string, sink + position, 0, element_length);
	position += element_length;
	}
	}
	}


	// Returns the result length of the concatenation.
	// On illegal argument, -1 is returned.
	static inline int StringBuilderConcatLength(int special_length,
	FixedArray* fixed_array,
	int array_length, bool* one_byte) {
	DisallowHeapAllocation no_gc;
	int position = 0;
	for (int i = 0; i < array_length; i++) {
	int increment = 0;
	Object* elt = fixed_array->get(i);
	if (elt->IsSmi()) {
	// Smi encoding of position and length.
	int smi_value = Smi::cast(elt)->value();
	int pos;
	int len;
	if (smi_value > 0) {
	// Position and length encoded in one smi.
	pos = StringBuilderSubstringPosition::decode(smi_value);
	len = StringBuilderSubstringLength::decode(smi_value);
	} else {
	// Position and length encoded in two smis.
	len = -smi_value;
	// Get the position and check that it is a positive smi.
	i++;
	if (i >= array_length) return -1;
	Object* next_smi = fixed_array->get(i);
	if (!next_smi->IsSmi()) return -1;
	pos = Smi::cast(next_smi)->value();
	if (pos < 0) return -1;
	}
	DCHECK(pos >= 0);
	DCHECK(len >= 0);
	if (pos > special_length \|\| len > special_length - pos) return -1;
	increment = len;
	} else if (elt->IsString()) {
	String* element = String::cast(elt);
	int element_length = element->length();
	increment = element_length;
	if (*one_byte && !element->HasOnlyOneByteChars()) {
	*one_byte = false;
	}
	} else {
	return -1;
	}
	if (increment > String::kMaxLength - position) {
	return kMaxInt; // Provoke throw on allocation.
	}
	position += increment;
	}
	return position;
	}


	class FixedArrayBuilder {
	public:
	explicit FixedArrayBuilder(Isolate* isolate, int initial_capacity)
	: array_(isolate->factory()->NewFixedArrayWithHoles(initial_capacity)),
	length_(0),
	has_non_smi_elements_(false) {
	// Require a non-zero initial size. Ensures that doubling the size to
	// extend the array will work.
	DCHECK(initial_capacity > 0);
	}

	explicit FixedArrayBuilder(Handle<FixedArray> backing_store)
	: array_(backing_store), length_(0), has_non_smi_elements_(false) {
	// Require a non-zero initial size. Ensures that doubling the size to
	// extend the array will work.
	DCHECK(backing_store->length() > 0);
	}

	bool HasCapacity(int elements) {
	int length = array_->length();
	int required_length = length_ + elements;
	return (length >= required_length);
	}

	void EnsureCapacity(int elements) {
	int length = array_->length();
	int required_length = length_ + elements;
	if (length < required_length) {
	int new_length = length;
	do {
	new_length *= 2;
	} while (new_length < required_length);
	Handle<FixedArray> extended_array =
	array_->GetIsolate()->factory()->NewFixedArrayWithHoles(new_length);
	array_->CopyTo(0, *extended_array, 0, length_);
	array_ = extended_array;
	}
	}

	void Add(Object* value) {
	DCHECK(!value->IsSmi());
	DCHECK(length_ < capacity());
	array_->set(length_, value);
	length_++;
	has_non_smi_elements_ = true;
	}

	void Add(Smi* value) {
	DCHECK(value->IsSmi());
	DCHECK(length_ < capacity());
	array_->set(length_, value);
	length_++;
	}

	Handle<FixedArray> array() { return array_; }

	int length() { return length_; }

	int capacity() { return array_->length(); }

	Handle<JSArray> ToJSArray(Handle<JSArray> target_array) {
	JSArray::SetContent(target_array, array_);
	target_array->set_length(Smi::FromInt(length_));
	return target_array;
	}

	private:
	Handle<FixedArray> array_;
	int length_;
	bool has_non_smi_elements_;
	};


	class ReplacementStringBuilder {
	public:
	ReplacementStringBuilder(Heap* heap, Handle<String> subject,
	int estimated_part_count)
	: heap_(heap),
	array_builder_(heap->isolate(), estimated_part_count),
	subject_(subject),
	character_count_(0),
	is_one_byte_(subject->IsOneByteRepresentation()) {
	// Require a non-zero initial size. Ensures that doubling the size to
	// extend the array will work.
	DCHECK(estimated_part_count > 0);
	}

	static inline void AddSubjectSlice(FixedArrayBuilder* builder, int from,
	int to) {
	DCHECK(from >= 0);
	int length = to - from;
	DCHECK(length > 0);
	if (StringBuilderSubstringLength::is_valid(length) &&
	StringBuilderSubstringPosition::is_valid(from)) {
	int encoded_slice = StringBuilderSubstringLength::encode(length) \|
	StringBuilderSubstringPosition::encode(from);
	builder->Add(Smi::FromInt(encoded_slice));
	} else {
	// Otherwise encode as two smis.
	builder->Add(Smi::FromInt(-length));
	builder->Add(Smi::FromInt(from));
	}
	}


	void EnsureCapacity(int elements) { array_builder_.EnsureCapacity(elements); }


	void AddSubjectSlice(int from, int to) {
	AddSubjectSlice(&array_builder_, from, to);
	IncrementCharacterCount(to - from);
	}


	void AddString(Handle<String> string) {
	int length = string->length();
	DCHECK(length > 0);
	AddElement(*string);
	if (!string->IsOneByteRepresentation()) {
	is_one_byte_ = false;
	}
	IncrementCharacterCount(length);
	}


	MaybeHandle<String> ToString();


	void IncrementCharacterCount(int by) {
	if (character_count_ > String::kMaxLength - by) {
	STATIC_ASSERT(String::kMaxLength < kMaxInt);
	character_count_ = kMaxInt;
	} else {
	character_count_ += by;
	}
	}

	private:
	void AddElement(Object* element) {
	DCHECK(element->IsSmi() \|\| element->IsString());
	DCHECK(array_builder_.capacity() > array_builder_.length());
	array_builder_.Add(element);
	}

	Heap* heap_;
	FixedArrayBuilder array_builder_;
	Handle<String> subject_;
	int character_count_;
	bool is_one_byte_;
	};


	class IncrementalStringBuilder {
	public:
	explicit IncrementalStringBuilder(Isolate* isolate);

	INLINE(String::Encoding CurrentEncoding()) { return encoding_; }

	template <typename SrcChar, typename DestChar>
	INLINE(void Append(SrcChar c));

	INLINE(void AppendCharacter(uint8_t c)) {
	if (encoding_ == String::ONE_BYTE_ENCODING) {
	Append<uint8_t, uint8_t>(c);
	} else {
	Append<uint8_t, uc16>(c);
	}
	}

	INLINE(void AppendCString(const char* s)) {
	const uint8_t* u = reinterpret_cast<const uint8_t*>(s);
	if (encoding_ == String::ONE_BYTE_ENCODING) {
	while (u != '\0') Append<uint8_t, uint8_t>((u++));
	} else {
	while (u != '\0') Append<uint8_t, uc16>((u++));
	}
	}

	INLINE(void AppendCString(const uc16* s)) {
	if (encoding_ == String::ONE_BYTE_ENCODING) {
	while (s != '\0') Append<uc16, uint8_t>((s++));
	} else {
	while (s != '\0') Append<uc16, uc16>((s++));
	}
	}

	INLINE(bool CurrentPartCanFit(int length)) {
	return part_length_ - current_index_ > length;
	}

	void AppendString(Handle<String> string);

	MaybeHandle<String> Finish();

	INLINE(bool HasOverflowed()) const { return overflowed_; }

	// Change encoding to two-byte.
	void ChangeEncoding() {
	DCHECK_EQ(String::ONE_BYTE_ENCODING, encoding_);
	ShrinkCurrentPart();
	encoding_ = String::TWO_BYTE_ENCODING;
	Extend();
	}

	template <typename DestChar>
	class NoExtend {
	public:
	explicit NoExtend(Handle<String> string, int offset) {
	DCHECK(string->IsSeqOneByteString() \|\| string->IsSeqTwoByteString());
	if (sizeof(DestChar) == 1) {
	start_ = reinterpret_cast<DestChar*>(
	Handle<SeqOneByteString>::cast(string)->GetChars() + offset);
	} else {
	start_ = reinterpret_cast<DestChar*>(
	Handle<SeqTwoByteString>::cast(string)->GetChars() + offset);
	}
	cursor_ = start_;
	}

	INLINE(void Append(DestChar c)) { *(cursor_++) = c; }
	INLINE(void AppendCString(const char* s)) {
	const uint8_t* u = reinterpret_cast<const uint8_t*>(s);
	while (u != '\0') Append((u++));
	}

	int written() { return static_cast<int>(cursor_ - start_); }

	private:
	DestChar* start_;
	DestChar* cursor_;
	DisallowHeapAllocation no_gc_;
	};

	template <typename DestChar>
	class NoExtendString : public NoExtend<DestChar> {
	public:
	NoExtendString(Handle<String> string, int required_length)
	: NoExtend<DestChar>(string, 0), string_(string) {
	DCHECK(string->length() >= required_length);
	}

	Handle<String> Finalize() {
	Handle<SeqString> string = Handle<SeqString>::cast(string_);
	int length = NoExtend<DestChar>::written();
	Handle<String> result = SeqString::Truncate(string, length);
	string_ = Handle<String>();
	return result;
	}

	private:
	Handle<String> string_;
	};

	template <typename DestChar>
	class NoExtendBuilder : public NoExtend<DestChar> {
	public:
	NoExtendBuilder(IncrementalStringBuilder* builder, int required_length)
	: NoExtend<DestChar>(builder->current_part(), builder->current_index_),
	builder_(builder) {
	DCHECK(builder->CurrentPartCanFit(required_length));
	}

	~NoExtendBuilder() {
	builder_->current_index_ += NoExtend<DestChar>::written();
	}

	private:
	IncrementalStringBuilder* builder_;
	};

	private:
	Factory* factory() { return isolate_->factory(); }

	INLINE(Handle<String> accumulator()) { return accumulator_; }

	INLINE(void set_accumulator(Handle<String> string)) {
	accumulator_.location() = string;
	}

	INLINE(Handle<String> current_part()) { return current_part_; }

	INLINE(void set_current_part(Handle<String> string)) {
	current_part_.location() = string;
	}

	// Add the current part to the accumulator.
	void Accumulate(Handle<String> new_part);

	// Finish the current part and allocate a new part.
	void Extend();

	// Shrink current part to the right size.
	void ShrinkCurrentPart() {
	DCHECK(current_index_ < part_length_);
	set_current_part(SeqString::Truncate(
	Handle<SeqString>::cast(current_part()), current_index_));
	}

	static const int kInitialPartLength = 32;
	static const int kMaxPartLength = 16 * 1024;
	static const int kPartLengthGrowthFactor = 2;

	Isolate* isolate_;
	String::Encoding encoding_;
	bool overflowed_;
	int part_length_;
	int current_index_;
	Handle<String> accumulator_;
	Handle<String> current_part_;
	};


	template <typename SrcChar, typename DestChar>
	void IncrementalStringBuilder::Append(SrcChar c) {
	DCHECK_EQ(encoding_ == String::ONE_BYTE_ENCODING, sizeof(DestChar) == 1);
	if (sizeof(DestChar) == 1) {
	DCHECK_EQ(String::ONE_BYTE_ENCODING, encoding_);
	SeqOneByteString::cast(*current_part_)
	->SeqOneByteStringSet(current_index_++, c);
	} else {
	DCHECK_EQ(String::TWO_BYTE_ENCODING, encoding_);
	SeqTwoByteString::cast(*current_part_)
	->SeqTwoByteStringSet(current_index_++, c);
	}
	if (current_index_ == part_length_) Extend();
	}
	} // namespace internal
	} // namespace v8

	#endif // V8_STRING_BUILDER_H_