Move string-related runtime functions into separate files.

src/runtime/runtime-strings.cc

+// 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.
+
+#include "src/v8.h"
+
+#include "src/arguments.h"
+#include "src/jsregexp-inl.h"
+#include "src/jsregexp.h"
+#include "src/runtime/runtime.h"
+#include "src/runtime/runtime-utils.h"
+#include "src/runtime/string-builder.h"
+#include "src/string-search.h"
+
+namespace v8 {
+namespace internal {
+
+
+// This may return an empty MaybeHandle if an exception is thrown or
+// we abort due to reaching the recursion limit.
+MaybeHandle<String> StringReplaceOneCharWithString(
+    Isolate* isolate, Handle<String> subject, Handle<String> search,
+    Handle<String> replace, bool* found, int recursion_limit) {
+  StackLimitCheck stackLimitCheck(isolate);
+  if (stackLimitCheck.HasOverflowed() || (recursion_limit == 0)) {
+    return MaybeHandle<String>();
+  }
+  recursion_limit--;
+  if (subject->IsConsString()) {
+    ConsString* cons = ConsString::cast(*subject);
+    Handle<String> first = Handle<String>(cons->first());
+    Handle<String> second = Handle<String>(cons->second());
+    Handle<String> new_first;
+    if (!StringReplaceOneCharWithString(isolate, first, search, replace, found,
+                                        recursion_limit).ToHandle(&new_first)) {
+      return MaybeHandle<String>();
+    }
+    if (*found) return isolate->factory()->NewConsString(new_first, second);
+
+    Handle<String> new_second;
+    if (!StringReplaceOneCharWithString(isolate, second, search, replace, found,
+                                        recursion_limit)
+             .ToHandle(&new_second)) {
+      return MaybeHandle<String>();
+    }
+    if (*found) return isolate->factory()->NewConsString(first, new_second);
+
+    return subject;
+  } else {
+    int index = Runtime::StringMatch(isolate, subject, search, 0);
+    if (index == -1) return subject;
+    *found = true;
+    Handle<String> first = isolate->factory()->NewSubString(subject, 0, index);
+    Handle<String> cons1;
+    ASSIGN_RETURN_ON_EXCEPTION(
+        isolate, cons1, isolate->factory()->NewConsString(first, replace),
+        String);
+    Handle<String> second =
+        isolate->factory()->NewSubString(subject, index + 1, subject->length());
+    return isolate->factory()->NewConsString(cons1, second);
+  }
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringReplaceOneCharWithString) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 3);
+  CONVERT_ARG_HANDLE_CHECKED(String, subject, 0);
+  CONVERT_ARG_HANDLE_CHECKED(String, search, 1);
+  CONVERT_ARG_HANDLE_CHECKED(String, replace, 2);
+
+  // If the cons string tree is too deep, we simply abort the recursion and
+  // retry with a flattened subject string.
+  const int kRecursionLimit = 0x1000;
+  bool found = false;
+  Handle<String> result;
+  if (StringReplaceOneCharWithString(isolate, subject, search, replace, &found,
+                                     kRecursionLimit).ToHandle(&result)) {
+    return *result;
+  }
+  if (isolate->has_pending_exception()) return isolate->heap()->exception();
+
+  subject = String::Flatten(subject);
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+      isolate, result,
+      StringReplaceOneCharWithString(isolate, subject, search, replace, &found,
+                                     kRecursionLimit));
+  return *result;
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringIndexOf) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 3);
+
+  CONVERT_ARG_HANDLE_CHECKED(String, sub, 0);
+  CONVERT_ARG_HANDLE_CHECKED(String, pat, 1);
+  CONVERT_ARG_HANDLE_CHECKED(Object, index, 2);
+
+  uint32_t start_index;
+  if (!index->ToArrayIndex(&start_index)) return Smi::FromInt(-1);
+
+  RUNTIME_ASSERT(start_index <= static_cast<uint32_t>(sub->length()));
+  int position = Runtime::StringMatch(isolate, sub, pat, start_index);
+  return Smi::FromInt(position);
+}
+
+
+template <typename schar, typename pchar>
+static int StringMatchBackwards(Vector<const schar> subject,
+                                Vector<const pchar> pattern, int idx) {
+  int pattern_length = pattern.length();
+  DCHECK(pattern_length >= 1);
+  DCHECK(idx + pattern_length <= subject.length());
+
+  if (sizeof(schar) == 1 && sizeof(pchar) > 1) {
+    for (int i = 0; i < pattern_length; i++) {
+      uc16 c = pattern[i];
+      if (c > String::kMaxOneByteCharCode) {
+        return -1;
+      }
+    }
+  }
+
+  pchar pattern_first_char = pattern[0];
+  for (int i = idx; i >= 0; i--) {
+    if (subject[i] != pattern_first_char) continue;
+    int j = 1;
+    while (j < pattern_length) {
+      if (pattern[j] != subject[i + j]) {
+        break;
+      }
+      j++;
+    }
+    if (j == pattern_length) {
+      return i;
+    }
+  }
+  return -1;
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringLastIndexOf) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 3);
+
+  CONVERT_ARG_HANDLE_CHECKED(String, sub, 0);
+  CONVERT_ARG_HANDLE_CHECKED(String, pat, 1);
+  CONVERT_ARG_HANDLE_CHECKED(Object, index, 2);
+
+  uint32_t start_index;
+  if (!index->ToArrayIndex(&start_index)) return Smi::FromInt(-1);
+
+  uint32_t pat_length = pat->length();
+  uint32_t sub_length = sub->length();
+
+  if (start_index + pat_length > sub_length) {
+    start_index = sub_length - pat_length;
+  }
+
+  if (pat_length == 0) {
+    return Smi::FromInt(start_index);
+  }
+
+  sub = String::Flatten(sub);
+  pat = String::Flatten(pat);
+
+  int position = -1;
+  DisallowHeapAllocation no_gc;  // ensure vectors stay valid
+
+  String::FlatContent sub_content = sub->GetFlatContent();
+  String::FlatContent pat_content = pat->GetFlatContent();
+
+  if (pat_content.IsOneByte()) {
+    Vector<const uint8_t> pat_vector = pat_content.ToOneByteVector();
+    if (sub_content.IsOneByte()) {
+      position = StringMatchBackwards(sub_content.ToOneByteVector(), pat_vector,
+                                      start_index);
+    } else {
+      position = StringMatchBackwards(sub_content.ToUC16Vector(), pat_vector,
+                                      start_index);
+    }
+  } else {
+    Vector<const uc16> pat_vector = pat_content.ToUC16Vector();
+    if (sub_content.IsOneByte()) {
+      position = StringMatchBackwards(sub_content.ToOneByteVector(), pat_vector,
+                                      start_index);
+    } else {
+      position = StringMatchBackwards(sub_content.ToUC16Vector(), pat_vector,
+                                      start_index);
+    }
+  }
+
+  return Smi::FromInt(position);
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringLocaleCompare) {
+  HandleScope handle_scope(isolate);
+  DCHECK(args.length() == 2);
+
+  CONVERT_ARG_HANDLE_CHECKED(String, str1, 0);
+  CONVERT_ARG_HANDLE_CHECKED(String, str2, 1);
+
+  if (str1.is_identical_to(str2)) return Smi::FromInt(0);  // Equal.
+  int str1_length = str1->length();
+  int str2_length = str2->length();
+
+  // Decide trivial cases without flattening.
+  if (str1_length == 0) {
+    if (str2_length == 0) return Smi::FromInt(0);  // Equal.
+    return Smi::FromInt(-str2_length);
+  } else {
+    if (str2_length == 0) return Smi::FromInt(str1_length);
+  }
+
+  int end = str1_length < str2_length ? str1_length : str2_length;
+
+  // No need to flatten if we are going to find the answer on the first
+  // character.  At this point we know there is at least one character
+  // in each string, due to the trivial case handling above.
+  int d = str1->Get(0) - str2->Get(0);
+  if (d != 0) return Smi::FromInt(d);
+
+  str1 = String::Flatten(str1);
+  str2 = String::Flatten(str2);
+
+  DisallowHeapAllocation no_gc;
+  String::FlatContent flat1 = str1->GetFlatContent();
+  String::FlatContent flat2 = str2->GetFlatContent();
+
+  for (int i = 0; i < end; i++) {
+    if (flat1.Get(i) != flat2.Get(i)) {
+      return Smi::FromInt(flat1.Get(i) - flat2.Get(i));
+    }
+  }
+
+  return Smi::FromInt(str1_length - str2_length);
+}
+
+
+RUNTIME_FUNCTION(Runtime_SubString) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 3);
+
+  CONVERT_ARG_HANDLE_CHECKED(String, string, 0);
+  int start, end;
+  // We have a fast integer-only case here to avoid a conversion to double in
+  // the common case where from and to are Smis.
+  if (args[1]->IsSmi() && args[2]->IsSmi()) {
+    CONVERT_SMI_ARG_CHECKED(from_number, 1);
+    CONVERT_SMI_ARG_CHECKED(to_number, 2);
+    start = from_number;
+    end = to_number;
+  } else {
+    CONVERT_DOUBLE_ARG_CHECKED(from_number, 1);
+    CONVERT_DOUBLE_ARG_CHECKED(to_number, 2);
+    start = FastD2IChecked(from_number);
+    end = FastD2IChecked(to_number);
+  }
+  RUNTIME_ASSERT(end >= start);
+  RUNTIME_ASSERT(start >= 0);
+  RUNTIME_ASSERT(end <= string->length());
+  isolate->counters()->sub_string_runtime()->Increment();
+
+  return *isolate->factory()->NewSubString(string, start, end);
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringAdd) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 2);
+  CONVERT_ARG_HANDLE_CHECKED(String, str1, 0);
+  CONVERT_ARG_HANDLE_CHECKED(String, str2, 1);
+  isolate->counters()->string_add_runtime()->Increment();
+  Handle<String> result;
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+      isolate, result, isolate->factory()->NewConsString(str1, str2));
+  return *result;
+}
+
+
+RUNTIME_FUNCTION(Runtime_InternalizeString) {
+  HandleScope handles(isolate);
+  RUNTIME_ASSERT(args.length() == 1);
+  CONVERT_ARG_HANDLE_CHECKED(String, string, 0);
+  return *isolate->factory()->InternalizeString(string);
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringMatch) {
+  HandleScope handles(isolate);
+  DCHECK(args.length() == 3);
+
+  CONVERT_ARG_HANDLE_CHECKED(String, subject, 0);
+  CONVERT_ARG_HANDLE_CHECKED(JSRegExp, regexp, 1);
+  CONVERT_ARG_HANDLE_CHECKED(JSArray, regexp_info, 2);
+
+  RUNTIME_ASSERT(regexp_info->HasFastObjectElements());
+
+  RegExpImpl::GlobalCache global_cache(regexp, subject, true, isolate);
+  if (global_cache.HasException()) return isolate->heap()->exception();
+
+  int capture_count = regexp->CaptureCount();
+
+  ZoneScope zone_scope(isolate->runtime_zone());
+  ZoneList<int> offsets(8, zone_scope.zone());
+
+  while (true) {
+    int32_t* match = global_cache.FetchNext();
+    if (match == NULL) break;
+    offsets.Add(match[0], zone_scope.zone());  // start
+    offsets.Add(match[1], zone_scope.zone());  // end
+  }
+
+  if (global_cache.HasException()) return isolate->heap()->exception();
+
+  if (offsets.length() == 0) {
+    // Not a single match.
+    return isolate->heap()->null_value();
+  }
+
+  RegExpImpl::SetLastMatchInfo(regexp_info, subject, capture_count,
+                               global_cache.LastSuccessfulMatch());
+
+  int matches = offsets.length() / 2;
+  Handle<FixedArray> elements = isolate->factory()->NewFixedArray(matches);
+  Handle<String> substring =
+      isolate->factory()->NewSubString(subject, offsets.at(0), offsets.at(1));
+  elements->set(0, *substring);
+  for (int i = 1; i < matches; i++) {
+    HandleScope temp_scope(isolate);
+    int from = offsets.at(i * 2);
+    int to = offsets.at(i * 2 + 1);
+    Handle<String> substring =
+        isolate->factory()->NewProperSubString(subject, from, to);
+    elements->set(i, *substring);
+  }
+  Handle<JSArray> result = isolate->factory()->NewJSArrayWithElements(elements);
+  result->set_length(Smi::FromInt(matches));
+  return *result;
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringCharCodeAtRT) {
+  HandleScope handle_scope(isolate);
+  DCHECK(args.length() == 2);
+
+  CONVERT_ARG_HANDLE_CHECKED(String, subject, 0);
+  CONVERT_NUMBER_CHECKED(uint32_t, i, Uint32, args[1]);
+
+  // Flatten the string.  If someone wants to get a char at an index
+  // in a cons string, it is likely that more indices will be
+  // accessed.
+  subject = String::Flatten(subject);
+
+  if (i >= static_cast<uint32_t>(subject->length())) {
+    return isolate->heap()->nan_value();
+  }
+
+  return Smi::FromInt(subject->Get(i));
+}
+
+
+RUNTIME_FUNCTION(Runtime_CharFromCode) {
+  HandleScope handlescope(isolate);
+  DCHECK(args.length() == 1);
+  if (args[0]->IsNumber()) {
+    CONVERT_NUMBER_CHECKED(uint32_t, code, Uint32, args[0]);
+    code &= 0xffff;
+    return *isolate->factory()->LookupSingleCharacterStringFromCode(code);
+  }
+  return isolate->heap()->empty_string();
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringCompare) {
+  HandleScope handle_scope(isolate);
+  DCHECK(args.length() == 2);
+
+  CONVERT_ARG_HANDLE_CHECKED(String, x, 0);
+  CONVERT_ARG_HANDLE_CHECKED(String, y, 1);
+
+  isolate->counters()->string_compare_runtime()->Increment();
+
+  // A few fast case tests before we flatten.
+  if (x.is_identical_to(y)) return Smi::FromInt(EQUAL);
+  if (y->length() == 0) {
+    if (x->length() == 0) return Smi::FromInt(EQUAL);
+    return Smi::FromInt(GREATER);
+  } else if (x->length() == 0) {
+    return Smi::FromInt(LESS);
+  }
+
+  int d = x->Get(0) - y->Get(0);
+  if (d < 0)
+    return Smi::FromInt(LESS);
+  else if (d > 0)
+    return Smi::FromInt(GREATER);
+
+  // Slow case.
+  x = String::Flatten(x);
+  y = String::Flatten(y);
+
+  DisallowHeapAllocation no_gc;
+  Object* equal_prefix_result = Smi::FromInt(EQUAL);
+  int prefix_length = x->length();
+  if (y->length() < prefix_length) {
+    prefix_length = y->length();
+    equal_prefix_result = Smi::FromInt(GREATER);
+  } else if (y->length() > prefix_length) {
+    equal_prefix_result = Smi::FromInt(LESS);
+  }
+  int r;
+  String::FlatContent x_content = x->GetFlatContent();
+  String::FlatContent y_content = y->GetFlatContent();
+  if (x_content.IsOneByte()) {
+    Vector<const uint8_t> x_chars = x_content.ToOneByteVector();
+    if (y_content.IsOneByte()) {
+      Vector<const uint8_t> y_chars = y_content.ToOneByteVector();
+      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
+    } else {
+      Vector<const uc16> y_chars = y_content.ToUC16Vector();
+      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
+    }
+  } else {
+    Vector<const uc16> x_chars = x_content.ToUC16Vector();
+    if (y_content.IsOneByte()) {
+      Vector<const uint8_t> y_chars = y_content.ToOneByteVector();
+      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
+    } else {
+      Vector<const uc16> y_chars = y_content.ToUC16Vector();
+      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
+    }
+  }
+  Object* result;
+  if (r == 0) {
+    result = equal_prefix_result;
+  } else {
+    result = (r < 0) ? Smi::FromInt(LESS) : Smi::FromInt(GREATER);
+  }
+  return result;
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringBuilderConcat) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 3);
+  CONVERT_ARG_HANDLE_CHECKED(JSArray, array, 0);
+  int32_t array_length;
+  if (!args[1]->ToInt32(&array_length)) {
+    THROW_NEW_ERROR_RETURN_FAILURE(isolate, NewInvalidStringLengthError());
+  }
+  CONVERT_ARG_HANDLE_CHECKED(String, special, 2);
+
+  size_t actual_array_length = 0;
+  RUNTIME_ASSERT(
+      TryNumberToSize(isolate, array->length(), &actual_array_length));
+  RUNTIME_ASSERT(array_length >= 0);
+  RUNTIME_ASSERT(static_cast<size_t>(array_length) <= actual_array_length);
+
+  // This assumption is used by the slice encoding in one or two smis.
+  DCHECK(Smi::kMaxValue >= String::kMaxLength);
+
+  RUNTIME_ASSERT(array->HasFastElements());
+  JSObject::EnsureCanContainHeapObjectElements(array);
+
+  int special_length = special->length();
+  if (!array->HasFastObjectElements()) {
+    return isolate->Throw(isolate->heap()->illegal_argument_string());
+  }
+
+  int length;
+  bool one_byte = special->HasOnlyOneByteChars();
+
+  {
+    DisallowHeapAllocation no_gc;
+    FixedArray* fixed_array = FixedArray::cast(array->elements());
+    if (fixed_array->length() < array_length) {
+      array_length = fixed_array->length();
+    }
+
+    if (array_length == 0) {
+      return isolate->heap()->empty_string();
+    } else if (array_length == 1) {
+      Object* first = fixed_array->get(0);
+      if (first->IsString()) return first;
+    }
+    length = StringBuilderConcatLength(special_length, fixed_array,
+                                       array_length, &one_byte);
+  }
+
+  if (length == -1) {
+    return isolate->Throw(isolate->heap()->illegal_argument_string());
+  }
+
+  if (one_byte) {
+    Handle<SeqOneByteString> answer;
+    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+        isolate, answer, isolate->factory()->NewRawOneByteString(length));
+    StringBuilderConcatHelper(*special, answer->GetChars(),
+                              FixedArray::cast(array->elements()),
+                              array_length);
+    return *answer;
+  } else {
+    Handle<SeqTwoByteString> answer;
+    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+        isolate, answer, isolate->factory()->NewRawTwoByteString(length));
+    StringBuilderConcatHelper(*special, answer->GetChars(),
+                              FixedArray::cast(array->elements()),
+                              array_length);
+    return *answer;
+  }
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringBuilderJoin) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 3);
+  CONVERT_ARG_HANDLE_CHECKED(JSArray, array, 0);
+  int32_t array_length;
+  if (!args[1]->ToInt32(&array_length)) {
+    THROW_NEW_ERROR_RETURN_FAILURE(isolate, NewInvalidStringLengthError());
+  }
+  CONVERT_ARG_HANDLE_CHECKED(String, separator, 2);
+  RUNTIME_ASSERT(array->HasFastObjectElements());
+  RUNTIME_ASSERT(array_length >= 0);
+
+  Handle<FixedArray> fixed_array(FixedArray::cast(array->elements()));
+  if (fixed_array->length() < array_length) {
+    array_length = fixed_array->length();
+  }
+
+  if (array_length == 0) {
+    return isolate->heap()->empty_string();
+  } else if (array_length == 1) {
+    Object* first = fixed_array->get(0);
+    RUNTIME_ASSERT(first->IsString());
+    return first;
+  }
+
+  int separator_length = separator->length();
+  RUNTIME_ASSERT(separator_length > 0);
+  int max_nof_separators =
+      (String::kMaxLength + separator_length - 1) / separator_length;
+  if (max_nof_separators < (array_length - 1)) {
+    THROW_NEW_ERROR_RETURN_FAILURE(isolate, NewInvalidStringLengthError());
+  }
+  int length = (array_length - 1) * separator_length;
+  for (int i = 0; i < array_length; i++) {
+    Object* element_obj = fixed_array->get(i);
+    RUNTIME_ASSERT(element_obj->IsString());
+    String* element = String::cast(element_obj);
+    int increment = element->length();
+    if (increment > String::kMaxLength - length) {
+      STATIC_ASSERT(String::kMaxLength < kMaxInt);
+      length = kMaxInt;  // Provoke exception;
+      break;
+    }
+    length += increment;
+  }
+
+  Handle<SeqTwoByteString> answer;
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+      isolate, answer, isolate->factory()->NewRawTwoByteString(length));
+
+  DisallowHeapAllocation no_gc;
+
+  uc16* sink = answer->GetChars();
+#ifdef DEBUG
+  uc16* end = sink + length;
+#endif
+
+  RUNTIME_ASSERT(fixed_array->get(0)->IsString());
+  String* first = String::cast(fixed_array->get(0));
+  String* separator_raw = *separator;
+  int first_length = first->length();
+  String::WriteToFlat(first, sink, 0, first_length);
+  sink += first_length;
+
+  for (int i = 1; i < array_length; i++) {
+    DCHECK(sink + separator_length <= end);
+    String::WriteToFlat(separator_raw, sink, 0, separator_length);
+    sink += separator_length;
+
+    RUNTIME_ASSERT(fixed_array->get(i)->IsString());
+    String* element = String::cast(fixed_array->get(i));
+    int element_length = element->length();
+    DCHECK(sink + element_length <= end);
+    String::WriteToFlat(element, sink, 0, element_length);
+    sink += element_length;
+  }
+  DCHECK(sink == end);
+
+  // Use %_FastOneByteArrayJoin instead.
+  DCHECK(!answer->IsOneByteRepresentation());
+  return *answer;
+}
+
+template <typename Char>
+static void JoinSparseArrayWithSeparator(FixedArray* elements,
+                                         int elements_length,
+                                         uint32_t array_length,
+                                         String* separator,
+                                         Vector<Char> buffer) {
+  DisallowHeapAllocation no_gc;
+  int previous_separator_position = 0;
+  int separator_length = separator->length();
+  int cursor = 0;
+  for (int i = 0; i < elements_length; i += 2) {
+    int position = NumberToInt32(elements->get(i));
+    String* string = String::cast(elements->get(i + 1));
+    int string_length = string->length();
+    if (string->length() > 0) {
+      while (previous_separator_position < position) {
+        String::WriteToFlat<Char>(separator, &buffer[cursor], 0,
+                                  separator_length);
+        cursor += separator_length;
+        previous_separator_position++;
+      }
+      String::WriteToFlat<Char>(string, &buffer[cursor], 0, string_length);
+      cursor += string->length();
+    }
+  }
+  if (separator_length > 0) {
+    // Array length must be representable as a signed 32-bit number,
+    // otherwise the total string length would have been too large.
+    DCHECK(array_length <= 0x7fffffff);  // Is int32_t.
+    int last_array_index = static_cast<int>(array_length - 1);
+    while (previous_separator_position < last_array_index) {
+      String::WriteToFlat<Char>(separator, &buffer[cursor], 0,
+                                separator_length);
+      cursor += separator_length;
+      previous_separator_position++;
+    }
+  }
+  DCHECK(cursor <= buffer.length());
+}
+
+
+RUNTIME_FUNCTION(Runtime_SparseJoinWithSeparator) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 3);
+  CONVERT_ARG_HANDLE_CHECKED(JSArray, elements_array, 0);
+  CONVERT_NUMBER_CHECKED(uint32_t, array_length, Uint32, args[1]);
+  CONVERT_ARG_HANDLE_CHECKED(String, separator, 2);
+  // elements_array is fast-mode JSarray of alternating positions
+  // (increasing order) and strings.
+  RUNTIME_ASSERT(elements_array->HasFastSmiOrObjectElements());
+  // array_length is length of original array (used to add separators);
+  // separator is string to put between elements. Assumed to be non-empty.
+  RUNTIME_ASSERT(array_length > 0);
+
+  // Find total length of join result.
+  int string_length = 0;
+  bool is_one_byte = separator->IsOneByteRepresentation();
+  bool overflow = false;
+  CONVERT_NUMBER_CHECKED(int, elements_length, Int32, elements_array->length());
+  RUNTIME_ASSERT(elements_length <= elements_array->elements()->length());
+  RUNTIME_ASSERT((elements_length & 1) == 0);  // Even length.
+  FixedArray* elements = FixedArray::cast(elements_array->elements());
+  for (int i = 0; i < elements_length; i += 2) {
+    RUNTIME_ASSERT(elements->get(i)->IsNumber());
+    CONVERT_NUMBER_CHECKED(uint32_t, position, Uint32, elements->get(i));
+    RUNTIME_ASSERT(position < array_length);
+    RUNTIME_ASSERT(elements->get(i + 1)->IsString());
+  }
+
+  {
+    DisallowHeapAllocation no_gc;
+    for (int i = 0; i < elements_length; i += 2) {
+      String* string = String::cast(elements->get(i + 1));
+      int length = string->length();
+      if (is_one_byte && !string->IsOneByteRepresentation()) {
+        is_one_byte = false;
+      }
+      if (length > String::kMaxLength ||
+          String::kMaxLength - length < string_length) {
+        overflow = true;
+        break;
+      }
+      string_length += length;
+    }
+  }
+
+  int separator_length = separator->length();
+  if (!overflow && separator_length > 0) {
+    if (array_length <= 0x7fffffffu) {
+      int separator_count = static_cast<int>(array_length) - 1;
+      int remaining_length = String::kMaxLength - string_length;
+      if ((remaining_length / separator_length) >= separator_count) {
+        string_length += separator_length * (array_length - 1);
+      } else {
+        // Not room for the separators within the maximal string length.
+        overflow = true;
+      }
+    } else {
+      // Nonempty separator and at least 2^31-1 separators necessary
+      // means that the string is too large to create.
+      STATIC_ASSERT(String::kMaxLength < 0x7fffffff);
+      overflow = true;
+    }
+  }
+  if (overflow) {
+    // Throw an exception if the resulting string is too large. See
+    // https://code.google.com/p/chromium/issues/detail?id=336820
+    // for details.
+    THROW_NEW_ERROR_RETURN_FAILURE(isolate, NewInvalidStringLengthError());
+  }
+
+  if (is_one_byte) {
+    Handle<SeqOneByteString> result = isolate->factory()
+                                          ->NewRawOneByteString(string_length)
+                                          .ToHandleChecked();
+    JoinSparseArrayWithSeparator<uint8_t>(
+        FixedArray::cast(elements_array->elements()), elements_length,
+        array_length, *separator,
+        Vector<uint8_t>(result->GetChars(), string_length));
+    return *result;
+  } else {
+    Handle<SeqTwoByteString> result = isolate->factory()
+                                          ->NewRawTwoByteString(string_length)
+                                          .ToHandleChecked();
+    JoinSparseArrayWithSeparator<uc16>(
+        FixedArray::cast(elements_array->elements()), elements_length,
+        array_length, *separator,
+        Vector<uc16>(result->GetChars(), string_length));
+    return *result;
+  }
+}
+
+
+// Copies Latin1 characters to the given fixed array looking up
+// one-char strings in the cache. Gives up on the first char that is
+// not in the cache and fills the remainder with smi zeros. Returns
+// the length of the successfully copied prefix.
+static int CopyCachedOneByteCharsToArray(Heap* heap, const uint8_t* chars,
+                                         FixedArray* elements, int length) {
+  DisallowHeapAllocation no_gc;
+  FixedArray* one_byte_cache = heap->single_character_string_cache();
+  Object* undefined = heap->undefined_value();
+  int i;
+  WriteBarrierMode mode = elements->GetWriteBarrierMode(no_gc);
+  for (i = 0; i < length; ++i) {
+    Object* value = one_byte_cache->get(chars[i]);
+    if (value == undefined) break;
+    elements->set(i, value, mode);
+  }
+  if (i < length) {
+    DCHECK(Smi::FromInt(0) == 0);
+    memset(elements->data_start() + i, 0, kPointerSize * (length - i));
+  }
+#ifdef DEBUG
+  for (int j = 0; j < length; ++j) {
+    Object* element = elements->get(j);
+    DCHECK(element == Smi::FromInt(0) ||
+           (element->IsString() && String::cast(element)->LooksValid()));
+  }
+#endif
+  return i;
+}
+
+
+// Converts a String to JSArray.
+// For example, "foo" => ["f", "o", "o"].
+RUNTIME_FUNCTION(Runtime_StringToArray) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 2);
+  CONVERT_ARG_HANDLE_CHECKED(String, s, 0);
+  CONVERT_NUMBER_CHECKED(uint32_t, limit, Uint32, args[1]);
+
+  s = String::Flatten(s);
+  const int length = static_cast<int>(Min<uint32_t>(s->length(), limit));
+
+  Handle<FixedArray> elements;
+  int position = 0;
+  if (s->IsFlat() && s->IsOneByteRepresentation()) {
+    // Try using cached chars where possible.
+    elements = isolate->factory()->NewUninitializedFixedArray(length);
+
+    DisallowHeapAllocation no_gc;
+    String::FlatContent content = s->GetFlatContent();
+    if (content.IsOneByte()) {
+      Vector<const uint8_t> chars = content.ToOneByteVector();
+      // Note, this will initialize all elements (not only the prefix)
+      // to prevent GC from seeing partially initialized array.
+      position = CopyCachedOneByteCharsToArray(isolate->heap(), chars.start(),
+                                               *elements, length);
+    } else {
+      MemsetPointer(elements->data_start(), isolate->heap()->undefined_value(),
+                    length);
+    }
+  } else {
+    elements = isolate->factory()->NewFixedArray(length);
+  }
+  for (int i = position; i < length; ++i) {
+    Handle<Object> str =
+        isolate->factory()->LookupSingleCharacterStringFromCode(s->Get(i));
+    elements->set(i, *str);
+  }
+
+#ifdef DEBUG
+  for (int i = 0; i < length; ++i) {
+    DCHECK(String::cast(elements->get(i))->length() == 1);
+  }
+#endif
+
+  return *isolate->factory()->NewJSArrayWithElements(elements);
+}
+
+
+static inline bool ToUpperOverflows(uc32 character) {
+  // y with umlauts and the micro sign are the only characters that stop
+  // fitting into one-byte when converting to uppercase.
+  static const uc32 yuml_code = 0xff;
+  static const uc32 micro_code = 0xb5;
+  return (character == yuml_code || character == micro_code);
+}
+
+
+template <class Converter>
+MUST_USE_RESULT static Object* ConvertCaseHelper(
+    Isolate* isolate, String* string, SeqString* result, int result_length,
+    unibrow::Mapping<Converter, 128>* mapping) {
+  DisallowHeapAllocation no_gc;
+  // We try this twice, once with the assumption that the result is no longer
+  // than the input and, if that assumption breaks, again with the exact
+  // length.  This may not be pretty, but it is nicer than what was here before
+  // and I hereby claim my vaffel-is.
+  //
+  // NOTE: This assumes that the upper/lower case of an ASCII
+  // character is also ASCII.  This is currently the case, but it
+  // might break in the future if we implement more context and locale
+  // dependent upper/lower conversions.
+  bool has_changed_character = false;
+
+  // Convert all characters to upper case, assuming that they will fit
+  // in the buffer
+  Access<ConsStringIteratorOp> op(isolate->runtime_state()->string_iterator());
+  StringCharacterStream stream(string, op.value());
+  unibrow::uchar chars[Converter::kMaxWidth];
+  // We can assume that the string is not empty
+  uc32 current = stream.GetNext();
+  bool ignore_overflow = Converter::kIsToLower || result->IsSeqTwoByteString();
+  for (int i = 0; i < result_length;) {
+    bool has_next = stream.HasMore();
+    uc32 next = has_next ? stream.GetNext() : 0;
+    int char_length = mapping->get(current, next, chars);
+    if (char_length == 0) {
+      // The case conversion of this character is the character itself.
+      result->Set(i, current);
+      i++;
+    } else if (char_length == 1 &&
+               (ignore_overflow || !ToUpperOverflows(current))) {
+      // Common case: converting the letter resulted in one character.
+      DCHECK(static_cast<uc32>(chars[0]) != current);
+      result->Set(i, chars[0]);
+      has_changed_character = true;
+      i++;
+    } else if (result_length == string->length()) {
+      bool overflows = ToUpperOverflows(current);
+      // We've assumed that the result would be as long as the
+      // input but here is a character that converts to several
+      // characters.  No matter, we calculate the exact length
+      // of the result and try the whole thing again.
+      //
+      // Note that this leaves room for optimization.  We could just
+      // memcpy what we already have to the result string.  Also,
+      // the result string is the last object allocated we could
+      // "realloc" it and probably, in the vast majority of cases,
+      // extend the existing string to be able to hold the full
+      // result.
+      int next_length = 0;
+      if (has_next) {
+        next_length = mapping->get(next, 0, chars);
+        if (next_length == 0) next_length = 1;
+      }
+      int current_length = i + char_length + next_length;
+      while (stream.HasMore()) {
+        current = stream.GetNext();
+        overflows |= ToUpperOverflows(current);
+        // NOTE: we use 0 as the next character here because, while
+        // the next character may affect what a character converts to,
+        // it does not in any case affect the length of what it convert
+        // to.
+        int char_length = mapping->get(current, 0, chars);
+        if (char_length == 0) char_length = 1;
+        current_length += char_length;
+        if (current_length > String::kMaxLength) {
+          AllowHeapAllocation allocate_error_and_return;
+          THROW_NEW_ERROR_RETURN_FAILURE(isolate,
+                                         NewInvalidStringLengthError());
+        }
+      }
+      // Try again with the real length.  Return signed if we need
+      // to allocate a two-byte string for to uppercase.
+      return (overflows && !ignore_overflow) ? Smi::FromInt(-current_length)
+                                             : Smi::FromInt(current_length);
+    } else {
+      for (int j = 0; j < char_length; j++) {
+        result->Set(i, chars[j]);
+        i++;
+      }
+      has_changed_character = true;
+    }
+    current = next;
+  }
+  if (has_changed_character) {
+    return result;
+  } else {
+    // If we didn't actually change anything in doing the conversion
+    // we simple return the result and let the converted string
+    // become garbage; there is no reason to keep two identical strings
+    // alive.
+    return string;
+  }
+}
+
+
+static const uintptr_t kOneInEveryByte = kUintptrAllBitsSet / 0xFF;
+static const uintptr_t kAsciiMask = kOneInEveryByte << 7;
+
+// Given a word and two range boundaries returns a word with high bit
+// set in every byte iff the corresponding input byte was strictly in
+// the range (m, n). All the other bits in the result are cleared.
+// This function is only useful when it can be inlined and the
+// boundaries are statically known.
+// Requires: all bytes in the input word and the boundaries must be
+// ASCII (less than 0x7F).
+static inline uintptr_t AsciiRangeMask(uintptr_t w, char m, char n) {
+  // Use strict inequalities since in edge cases the function could be
+  // further simplified.
+  DCHECK(0 < m && m < n);
+  // Has high bit set in every w byte less than n.
+  uintptr_t tmp1 = kOneInEveryByte * (0x7F + n) - w;
+  // Has high bit set in every w byte greater than m.
+  uintptr_t tmp2 = w + kOneInEveryByte * (0x7F - m);
+  return (tmp1 & tmp2 & (kOneInEveryByte * 0x80));
+}
+
+
+#ifdef DEBUG
+static bool CheckFastAsciiConvert(char* dst, const char* src, int length,
+                                  bool changed, bool is_to_lower) {
+  bool expected_changed = false;
+  for (int i = 0; i < length; i++) {
+    if (dst[i] == src[i]) continue;
+    expected_changed = true;
+    if (is_to_lower) {
+      DCHECK('A' <= src[i] && src[i] <= 'Z');
+      DCHECK(dst[i] == src[i] + ('a' - 'A'));
+    } else {
+      DCHECK('a' <= src[i] && src[i] <= 'z');
+      DCHECK(dst[i] == src[i] - ('a' - 'A'));
+    }
+  }
+  return (expected_changed == changed);
+}
+#endif
+
+
+template <class Converter>
+static bool FastAsciiConvert(char* dst, const char* src, int length,
+                             bool* changed_out) {
+#ifdef DEBUG
+  char* saved_dst = dst;
+  const char* saved_src = src;
+#endif
+  DisallowHeapAllocation no_gc;
+  // We rely on the distance between upper and lower case letters
+  // being a known power of 2.
+  DCHECK('a' - 'A' == (1 << 5));
+  // Boundaries for the range of input characters than require conversion.
+  static const char lo = Converter::kIsToLower ? 'A' - 1 : 'a' - 1;
+  static const char hi = Converter::kIsToLower ? 'Z' + 1 : 'z' + 1;
+  bool changed = false;
+  uintptr_t or_acc = 0;
+  const char* const limit = src + length;
+
+  // dst is newly allocated and always aligned.
+  DCHECK(IsAligned(reinterpret_cast<intptr_t>(dst), sizeof(uintptr_t)));
+  // Only attempt processing one word at a time if src is also aligned.
+  if (IsAligned(reinterpret_cast<intptr_t>(src), sizeof(uintptr_t))) {
+    // Process the prefix of the input that requires no conversion one aligned
+    // (machine) word at a time.
+    while (src <= limit - sizeof(uintptr_t)) {
+      const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src);
+      or_acc |= w;
+      if (AsciiRangeMask(w, lo, hi) != 0) {
+        changed = true;
+        break;
+      }
+      *reinterpret_cast<uintptr_t*>(dst) = w;
+      src += sizeof(uintptr_t);
+      dst += sizeof(uintptr_t);
+    }
+    // Process the remainder of the input performing conversion when
+    // required one word at a time.
+    while (src <= limit - sizeof(uintptr_t)) {
+      const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src);
+      or_acc |= w;
+      uintptr_t m = AsciiRangeMask(w, lo, hi);
+      // The mask has high (7th) bit set in every byte that needs
+      // conversion and we know that the distance between cases is
+      // 1 << 5.
+      *reinterpret_cast<uintptr_t*>(dst) = w ^ (m >> 2);
+      src += sizeof(uintptr_t);
+      dst += sizeof(uintptr_t);
+    }
+  }
+  // Process the last few bytes of the input (or the whole input if
+  // unaligned access is not supported).
+  while (src < limit) {
+    char c = *src;
+    or_acc |= c;
+    if (lo < c && c < hi) {
+      c ^= (1 << 5);
+      changed = true;
+    }
+    *dst = c;
+    ++src;
+    ++dst;
+  }
+
+  if ((or_acc & kAsciiMask) != 0) return false;
+
+  DCHECK(CheckFastAsciiConvert(saved_dst, saved_src, length, changed,
+                               Converter::kIsToLower));
+
+  *changed_out = changed;
+  return true;
+}
+
+
+template <class Converter>
+MUST_USE_RESULT static Object* ConvertCase(
+    Handle<String> s, Isolate* isolate,
+    unibrow::Mapping<Converter, 128>* mapping) {
+  s = String::Flatten(s);
+  int length = s->length();
+  // Assume that the string is not empty; we need this assumption later
+  if (length == 0) return *s;
+
+  // Simpler handling of ASCII strings.
+  //
+  // NOTE: This assumes that the upper/lower case of an ASCII
+  // character is also ASCII.  This is currently the case, but it
+  // might break in the future if we implement more context and locale
+  // dependent upper/lower conversions.
+  if (s->IsOneByteRepresentationUnderneath()) {
+    // Same length as input.
+    Handle<SeqOneByteString> result =
+        isolate->factory()->NewRawOneByteString(length).ToHandleChecked();
+    DisallowHeapAllocation no_gc;
+    String::FlatContent flat_content = s->GetFlatContent();
+    DCHECK(flat_content.IsFlat());
+    bool has_changed_character = false;
+    bool is_ascii = FastAsciiConvert<Converter>(
+        reinterpret_cast<char*>(result->GetChars()),
+        reinterpret_cast<const char*>(flat_content.ToOneByteVector().start()),
+        length, &has_changed_character);
+    // If not ASCII, we discard the result and take the 2 byte path.
+    if (is_ascii) return has_changed_character ? *result : *s;
+  }
+
+  Handle<SeqString> result;  // Same length as input.
+  if (s->IsOneByteRepresentation()) {
+    result = isolate->factory()->NewRawOneByteString(length).ToHandleChecked();
+  } else {
+    result = isolate->factory()->NewRawTwoByteString(length).ToHandleChecked();
+  }
+
+  Object* answer = ConvertCaseHelper(isolate, *s, *result, length, mapping);
+  if (answer->IsException() || answer->IsString()) return answer;
+
+  DCHECK(answer->IsSmi());
+  length = Smi::cast(answer)->value();
+  if (s->IsOneByteRepresentation() && length > 0) {
+    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+        isolate, result, isolate->factory()->NewRawOneByteString(length));
+  } else {
+    if (length < 0) length = -length;
+    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+        isolate, result, isolate->factory()->NewRawTwoByteString(length));
+  }
+  return ConvertCaseHelper(isolate, *s, *result, length, mapping);
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringToLowerCase) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 1);
+  CONVERT_ARG_HANDLE_CHECKED(String, s, 0);
+  return ConvertCase(s, isolate, isolate->runtime_state()->to_lower_mapping());
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringToUpperCase) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 1);
+  CONVERT_ARG_HANDLE_CHECKED(String, s, 0);
+  return ConvertCase(s, isolate, isolate->runtime_state()->to_upper_mapping());
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringTrim) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 3);
+
+  CONVERT_ARG_HANDLE_CHECKED(String, string, 0);
+  CONVERT_BOOLEAN_ARG_CHECKED(trimLeft, 1);
+  CONVERT_BOOLEAN_ARG_CHECKED(trimRight, 2);
+
+  string = String::Flatten(string);
+  int length = string->length();
+
+  int left = 0;
+  UnicodeCache* unicode_cache = isolate->unicode_cache();
+  if (trimLeft) {
+    while (left < length &&
+           unicode_cache->IsWhiteSpaceOrLineTerminator(string->Get(left))) {
+      left++;
+    }
+  }
+
+  int right = length;
+  if (trimRight) {
+    while (
+        right > left &&
+        unicode_cache->IsWhiteSpaceOrLineTerminator(string->Get(right - 1))) {
+      right--;
+    }
+  }
+
+  return *isolate->factory()->NewSubString(string, left, right);
+}
+
+
+RUNTIME_FUNCTION(Runtime_TruncateString) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 2);
+  CONVERT_ARG_HANDLE_CHECKED(SeqString, string, 0);
+  CONVERT_INT32_ARG_CHECKED(new_length, 1);
+  RUNTIME_ASSERT(new_length >= 0);
+  return *SeqString::Truncate(string, new_length);
+}
+
+
+RUNTIME_FUNCTION(Runtime_NewString) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 2);
+  CONVERT_INT32_ARG_CHECKED(length, 0);
+  CONVERT_BOOLEAN_ARG_CHECKED(is_one_byte, 1);
+  if (length == 0) return isolate->heap()->empty_string();
+  Handle<String> result;
+  if (is_one_byte) {
+    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+        isolate, result, isolate->factory()->NewRawOneByteString(length));
+  } else {
+    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+        isolate, result, isolate->factory()->NewRawTwoByteString(length));
+  }
+  return *result;
+}
+
+
+RUNTIME_FUNCTION(Runtime_StringEquals) {
+  HandleScope handle_scope(isolate);
+  DCHECK(args.length() == 2);
+
+  CONVERT_ARG_HANDLE_CHECKED(String, x, 0);
+  CONVERT_ARG_HANDLE_CHECKED(String, y, 1);
+
+  bool not_equal = !String::Equals(x, y);
+  // This is slightly convoluted because the value that signifies
+  // equality is 0 and inequality is 1 so we have to negate the result
+  // from String::Equals.
+  DCHECK(not_equal == 0 || not_equal == 1);
+  STATIC_ASSERT(EQUAL == 0);
+  STATIC_ASSERT(NOT_EQUAL == 1);
+  return Smi::FromInt(not_equal);
+}
+
+
+RUNTIME_FUNCTION(RuntimeReference_StringCharFromCode) {
+  SealHandleScope shs(isolate);
+  return __RT_impl_Runtime_CharFromCode(args, isolate);
+}
+
+
+RUNTIME_FUNCTION(RuntimeReference_StringCharAt) {
+  SealHandleScope shs(isolate);
+  DCHECK(args.length() == 2);
+  if (!args[0]->IsString()) return Smi::FromInt(0);
+  if (!args[1]->IsNumber()) return Smi::FromInt(0);
+  if (std::isinf(args.number_at(1))) return isolate->heap()->empty_string();
+  Object* code = __RT_impl_Runtime_StringCharCodeAtRT(args, isolate);
+  if (code->IsNaN()) return isolate->heap()->empty_string();
+  return __RT_impl_Runtime_CharFromCode(Arguments(1, &code), isolate);
+}
+
+
+RUNTIME_FUNCTION(RuntimeReference_OneByteSeqStringSetChar) {
+  SealHandleScope shs(isolate);
+  DCHECK(args.length() == 3);
+  CONVERT_INT32_ARG_CHECKED(index, 0);
+  CONVERT_INT32_ARG_CHECKED(value, 1);
+  CONVERT_ARG_CHECKED(SeqOneByteString, string, 2);
+  string->SeqOneByteStringSet(index, value);
+  return string;
+}
+
+
+RUNTIME_FUNCTION(RuntimeReference_TwoByteSeqStringSetChar) {
+  SealHandleScope shs(isolate);
+  DCHECK(args.length() == 3);
+  CONVERT_INT32_ARG_CHECKED(index, 0);
+  CONVERT_INT32_ARG_CHECKED(value, 1);
+  CONVERT_ARG_CHECKED(SeqTwoByteString, string, 2);
+  string->SeqTwoByteStringSet(index, value);
+  return string;
+}
+
+
+RUNTIME_FUNCTION(RuntimeReference_StringCompare) {
+  SealHandleScope shs(isolate);
+  return __RT_impl_Runtime_StringCompare(args, isolate);
+}
+
+
+RUNTIME_FUNCTION(RuntimeReference_StringCharCodeAt) {
+  SealHandleScope shs(isolate);
+  DCHECK(args.length() == 2);
+  if (!args[0]->IsString()) return isolate->heap()->undefined_value();
+  if (!args[1]->IsNumber()) return isolate->heap()->undefined_value();
+  if (std::isinf(args.number_at(1))) return isolate->heap()->nan_value();
+  return __RT_impl_Runtime_StringCharCodeAtRT(args, isolate);
+}
+
+
+RUNTIME_FUNCTION(RuntimeReference_SubString) {
+  SealHandleScope shs(isolate);
+  return __RT_impl_Runtime_SubString(args, isolate);
+}
+
+
+RUNTIME_FUNCTION(RuntimeReference_StringAdd) {
+  SealHandleScope shs(isolate);
+  return __RT_impl_Runtime_StringAdd(args, isolate);
+}
+}
+}  // namespace v8::internal