text: // Copyright 2012 the V8 project authors. All rights reserved.
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  //       notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  //       copyright notice, this list of conditions and the following
  //       disclaimer in the documentation and/or other materials provided
  //       with the distribution.
  //     * Neither the name of Google Inc. nor the names of its
  //       contributors may be used to endorse or promote products derived
  //       from this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  #ifndef V8_UTILS_H_
  #define V8_UTILS_H_
  
  #include <stdlib.h>
  #include <string.h>
  #include <algorithm>
  #include <climits>
  
  #include "allocation.h"
  #include "checks.h"
  #include "globals.h"
  
  namespace v8 {
  namespace internal {
  
  // ----------------------------------------------------------------------------
  // General helper functions
  
  #define IS_POWER_OF_TWO(x) (((x) & ((x) - 1)) == 0)
  
  // Returns true iff x is a power of 2 (or zero). Cannot be used with the
  // maximally negative value of the type T (the -1 overflows).
  template <typename T>
  inline bool IsPowerOf2(T x) {
    return IS_POWER_OF_TWO(x);
  }
  
  
  // X must be a power of 2.  Returns the number of trailing zeros.
  inline int WhichPowerOf2(uint32_t x) {
    ASSERT(IsPowerOf2(x));
    ASSERT(x != 0);
    int bits = 0;
  #ifdef DEBUG
    int original_x = x;
  #endif
    if (x >= 0x10000) {
      bits += 16;
      x >>= 16;
    }
    if (x >= 0x100) {
      bits += 8;
      x >>= 8;
    }
    if (x >= 0x10) {
      bits += 4;
      x >>= 4;
    }
    switch (x) {
      default: UNREACHABLE();
      case 8: bits++;  // Fall through.
      case 4: bits++;  // Fall through.
      case 2: bits++;  // Fall through.
      case 1: break;
    }
    ASSERT_EQ(1 << bits, original_x);
    return bits;
    return 0;
  }
  
  
  inline int MostSignificantBit(uint32_t x) {
    static const int msb4[] = {0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4};
    int nibble = 0;
    if (x & 0xffff0000) {
      nibble += 16;
      x >>= 16;
    }
    if (x & 0xff00) {
      nibble += 8;
      x >>= 8;
    }
    if (x & 0xf0) {
      nibble += 4;
      x >>= 4;
    }
    return nibble + msb4[x];
  }
  
  
  // Magic numbers for integer division.
  // These are kind of 2's complement reciprocal of the divisors.
  // Details and proofs can be found in:
  // - Hacker's Delight, Henry S. Warren, Jr.
  // - The PowerPC Compiler Writer’s Guide
  // and probably many others.
  // See details in the implementation of the algorithm in
  // lithium-codegen-arm.cc : LCodeGen::TryEmitSignedIntegerDivisionByConstant().
  struct DivMagicNumbers {
    unsigned M;
    unsigned s;
  };
  
  const DivMagicNumbers InvalidDivMagicNumber= {0, 0};
  const DivMagicNumbers DivMagicNumberFor3   = {0x55555556, 0};
  const DivMagicNumbers DivMagicNumberFor5   = {0x66666667, 1};
  const DivMagicNumbers DivMagicNumberFor7   = {0x92492493, 2};
  const DivMagicNumbers DivMagicNumberFor9   = {0x38e38e39, 1};
  const DivMagicNumbers DivMagicNumberFor11  = {0x2e8ba2e9, 1};
  const DivMagicNumbers DivMagicNumberFor25  = {0x51eb851f, 3};
  const DivMagicNumbers DivMagicNumberFor125 = {0x10624dd3, 3};
  const DivMagicNumbers DivMagicNumberFor625 = {0x68db8bad, 8};
  
  const DivMagicNumbers DivMagicNumberFor(int32_t divisor);
  
  
  // The C++ standard leaves the semantics of '>>' undefined for
  // negative signed operands. Most implementations do the right thing,
  // though.
  inline int ArithmeticShiftRight(int x, int s) {
    return x >> s;
  }
  
  
  // Compute the 0-relative offset of some absolute value x of type T.
  // This allows conversion of Addresses and integral types into
  // 0-relative int offsets.
  template <typename T>
  inline intptr_t OffsetFrom(T x) {
    return x - static_cast<T>(0);
  }
  
  
  // Compute the absolute value of type T for some 0-relative offset x.
  // This allows conversion of 0-relative int offsets into Addresses and
  // integral types.
  template <typename T>
  inline T AddressFrom(intptr_t x) {
    return static_cast<T>(static_cast<T>(0) + x);
  }
  
  
  // Return the largest multiple of m which is <= x.
  template <typename T>
  inline T RoundDown(T x, intptr_t m) {
    ASSERT(IsPowerOf2(m));
    return AddressFrom<T>(OffsetFrom(x) & -m);
  }
  
  
  // Return the smallest multiple of m which is >= x.
  template <typename T>
  inline T RoundUp(T x, intptr_t m) {
    return RoundDown<T>(static_cast<T>(x + m - 1), m);
  }
  
  
  template <typename T>
  int Compare(const T& a, const T& b) {
    if (a == b)
      return 0;
    else if (a < b)
      return -1;
    else
      return 1;
  }
  
  
  template <typename T>
  int PointerValueCompare(const T* a, const T* b) {
    return Compare<T>(*a, *b);
  }
  
  
  // Compare function to compare the object pointer value of two
  // handlified objects. The handles are passed as pointers to the
  // handles.
  template<typename T> class Handle;  // Forward declaration.
  template <typename T>
  int HandleObjectPointerCompare(const Handle<T>* a, const Handle<T>* b) {
    return Compare<T*>(*(*a), *(*b));
  }
  
  
  // Returns the smallest power of two which is >= x. If you pass in a
  // number that is already a power of two, it is returned as is.
  // Implementation is from "Hacker's Delight" by Henry S. Warren, Jr.,
  // figure 3-3, page 48, where the function is called clp2.
  inline uint32_t RoundUpToPowerOf2(uint32_t x) {
    ASSERT(x <= 0x80000000u);
    x = x - 1;
    x = x | (x >> 1);
    x = x | (x >> 2);
    x = x | (x >> 4);
    x = x | (x >> 8);
    x = x | (x >> 16);
    return x + 1;
  }
  
  
  inline uint32_t RoundDownToPowerOf2(uint32_t x) {
    uint32_t rounded_up = RoundUpToPowerOf2(x);
    if (rounded_up > x) return rounded_up >> 1;
    return rounded_up;
  }
  
  
  template <typename T, typename U>
  inline bool IsAligned(T value, U alignment) {
    return (value & (alignment - 1)) == 0;
  }
  
  
  // Returns true if (addr + offset) is aligned.
  inline bool IsAddressAligned(Address addr,
                               intptr_t alignment,
                               int offset = 0) {
    intptr_t offs = OffsetFrom(addr + offset);
    return IsAligned(offs, alignment);
  }
  
  
  // Returns the maximum of the two parameters.
  template <typename T>
  T Max(T a, T b) {
    return a < b ? b : a;
  }
  
  
  // Returns the minimum of the two parameters.
  template <typename T>
  T Min(T a, T b) {
    return a < b ? a : b;
  }
  
  
  // Returns the absolute value of its argument.
  template <typename T>
  T Abs(T a) {
    return a < 0 ? -a : a;
  }
  
  
  // Returns the negative absolute value of its argument.
  template <typename T>
  T NegAbs(T a) {
    return a < 0 ? a : -a;
  }
  
  
  inline int StrLength(const char* string) {
    size_t length = strlen(string);
    ASSERT(length == static_cast<size_t>(static_cast<int>(length)));
    return static_cast<int>(length);
  }
  
  
  // ----------------------------------------------------------------------------
  // BitField is a help template for encoding and decode bitfield with
  // unsigned content.
  
  template<class T, int shift, int size, class U>
  class BitFieldBase {
   public:
    // A type U mask of bit field.  To use all bits of a type U of x bits
    // in a bitfield without compiler warnings we have to compute 2^x
    // without using a shift count of x in the computation.
    static const U kOne = static_cast<U>(1U);
    static const U kMask = ((kOne << shift) << size) - (kOne << shift);
    static const U kShift = shift;
    static const U kSize = size;
  
    // Value for the field with all bits set.
    static const T kMax = static_cast<T>((1U << size) - 1);
  
    // Tells whether the provided value fits into the bit field.
    static bool is_valid(T value) {
      return (static_cast<U>(value) & ~static_cast<U>(kMax)) == 0;
    }
  
    // Returns a type U with the bit field value encoded.
    static U encode(T value) {
      ASSERT(is_valid(value));
      return static_cast<U>(value) << shift;
    }
  
    // Returns a type U with the bit field value updated.
    static U update(U previous, T value) {
      return (previous & ~kMask) | encode(value);
    }
  
    // Extracts the bit field from the value.
    static T decode(U value) {
      return static_cast<T>((value & kMask) >> shift);
    }
  };
  
  
  template<class T, int shift, int size>
  class BitField : public BitFieldBase<T, shift, size, uint32_t> { };
  
  
  template<class T, int shift, int size>
  class BitField64 : public BitFieldBase<T, shift, size, uint64_t> { };
  
  
  // ----------------------------------------------------------------------------
  // Hash function.
  
  static const uint32_t kZeroHashSeed = 0;
  
  // Thomas Wang, Integer Hash Functions.
  // http://www.concentric.net/~Ttwang/tech/inthash.htm
  inline uint32_t ComputeIntegerHash(uint32_t key, uint32_t seed) {
    uint32_t hash = key;
    hash = hash ^ seed;
    hash = ~hash + (hash << 15);  // hash = (hash << 15) - hash - 1;
    hash = hash ^ (hash >> 12);
    hash = hash + (hash << 2);
    hash = hash ^ (hash >> 4);
    hash = hash * 2057;  // hash = (hash + (hash << 3)) + (hash << 11);
    hash = hash ^ (hash >> 16);
    return hash;
  }
  
  
  inline uint32_t ComputeLongHash(uint64_t key) {
    uint64_t hash = key;
    hash = ~hash + (hash << 18);  // hash = (hash << 18) - hash - 1;
    hash = hash ^ (hash >> 31);
    hash = hash * 21;  // hash = (hash + (hash << 2)) + (hash << 4);
    hash = hash ^ (hash >> 11);
    hash = hash + (hash << 6);
    hash = hash ^ (hash >> 22);
    return static_cast<uint32_t>(hash);
  }
  
  
  inline uint32_t ComputePointerHash(void* ptr) {
    return ComputeIntegerHash(
        static_cast<uint32_t>(reinterpret_cast<intptr_t>(ptr)),
        v8::internal::kZeroHashSeed);
  }
  
  
  // ----------------------------------------------------------------------------
  // Miscellaneous
  
  // A static resource holds a static instance that can be reserved in
  // a local scope using an instance of Access.  Attempts to re-reserve
  // the instance will cause an error.
  template <typename T>
  class StaticResource {
   public:
    StaticResource() : is_reserved_(false)  {}
  
   private:
    template <typename S> friend class Access;
    T instance_;
    bool is_reserved_;
  };
  
  
  // Locally scoped access to a static resource.
  template <typename T>
  class Access {
   public:
    explicit Access(StaticResource<T>* resource)
      : resource_(resource)
      , instance_(&resource->instance_) {
      ASSERT(!resource->is_reserved_);
      resource->is_reserved_ = true;
    }
  
    ~Access() {
      resource_->is_reserved_ = false;
      resource_ = NULL;
      instance_ = NULL;
    }
  
    T* value()  { return instance_; }
    T* operator -> ()  { return instance_; }
  
   private:
    StaticResource<T>* resource_;
    T* instance_;
  };
  
  
  template <typename T>
  class Vector {
   public:
    Vector() : start_(NULL), length_(0) {}
    Vector(T* data, int length) : start_(data), length_(length) {
      ASSERT(length == 0 || (length > 0 && data != NULL));
    }
  
    static Vector<T> New(int length) {
      return Vector<T>(NewArray<T>(length), length);
    }
  
    // Returns a vector using the same backing storage as this one,
    // spanning from and including 'from', to but not including 'to'.
    Vector<T> SubVector(int from, int to) {
      SLOW_ASSERT(to <= length_);
      SLOW_ASSERT(from < to);
      ASSERT(0 <= from);
      return Vector<T>(start() + from, to - from);
    }
  
    // Returns the length of the vector.
    int length() const { return length_; }
  
    // Returns whether or not the vector is empty.
    bool is_empty() const { return length_ == 0; }
  
    // Returns the pointer to the start of the data in the vector.
    T* start() const { return start_; }
  
    // Access individual vector elements - checks bounds in debug mode.
    T& operator[](int index) const {
      ASSERT(0 <= index && index < length_);
      return start_[index];
    }
  
    const T& at(int index) const { return operator[](index); }
  
    T& first() { return start_[0]; }
  
    T& last() { return start_[length_ - 1]; }
  
    // Returns a clone of this vector with a new backing store.
    Vector<T> Clone() const {
      T* result = NewArray<T>(length_);
      for (int i = 0; i < length_; i++) result[i] = start_[i];
      return Vector<T>(result, length_);
    }
  
    void Sort(int (*cmp)(const T*, const T*)) {
      std::sort(start(), start() + length(), RawComparer(cmp));
    }
  
    void Sort() {
      std::sort(start(), start() + length());
    }
  
    void Truncate(int length) {
      ASSERT(length <= length_);
      length_ = length;
    }
  
    // Releases the array underlying this vector. Once disposed the
    // vector is empty.
    void Dispose() {
      DeleteArray(start_);
      start_ = NULL;
      length_ = 0;
    }
  
    inline Vector<T> operator+(int offset) {
      ASSERT(offset < length_);
      return Vector<T>(start_ + offset, length_ - offset);
    }
  
    // Factory method for creating empty vectors.
    static Vector<T> empty() { return Vector<T>(NULL, 0); }
  
    template<typename S>
    static Vector<T> cast(Vector<S> input) {
      return Vector<T>(reinterpret_cast<T*>(input.start()),
                       input.length() * sizeof(S) / sizeof(T));
    }
  
   protected:
    void set_start(T* start) { start_ = start; }
  
   private:
    T* start_;
    int length_;
  
    class RawComparer {
     public:
      explicit RawComparer(int (*cmp)(const T*, const T*)) : cmp_(cmp) {}
      bool operator()(const T& a, const T& b) {
        return cmp_(&a, &b) < 0;
      }
  
     private:
      int (*cmp_)(const T*, const T*);
    };
  };
  
  
  // A pointer that can only be set once and doesn't allow NULL values.
  template<typename T>
  class SetOncePointer {
   public:
    SetOncePointer() : pointer_(NULL) { }
  
    bool is_set() const { return pointer_ != NULL; }
  
    T* get() const {
      ASSERT(pointer_ != NULL);
      return pointer_;
    }
  
    void set(T* value) {
      ASSERT(pointer_ == NULL && value != NULL);
      pointer_ = value;
    }
  
   private:
    T* pointer_;
  };
  
  
  template <typename T, int kSize>
  class EmbeddedVector : public Vector<T> {
   public:
    EmbeddedVector() : Vector<T>(buffer_, kSize) { }
  
    explicit EmbeddedVector(T initial_value) : Vector<T>(buffer_, kSize) {
      for (int i = 0; i < kSize; ++i) {
        buffer_[i] = initial_value;
      }
    }
  
    // When copying, make underlying Vector to reference our buffer.
    EmbeddedVector(const EmbeddedVector& rhs)
        : Vector<T>(rhs) {
      // TODO(jkummerow): Refactor #includes and use OS::MemCopy() instead.
      memcpy(buffer_, rhs.buffer_, sizeof(T) * kSize);
      set_start(buffer_);
    }
  
    EmbeddedVector& operator=(const EmbeddedVector& rhs) {
      if (this == &rhs) return *this;
      Vector<T>::operator=(rhs);
      // TODO(jkummerow): Refactor #includes and use OS::MemCopy() instead.
      memcpy(buffer_, rhs.buffer_, sizeof(T) * kSize);
      this->set_start(buffer_);
      return *this;
    }
  
   private:
    T buffer_[kSize];
  };
  
  
  template <typename T>
  class ScopedVector : public Vector<T> {
   public:
    explicit ScopedVector(int length) : Vector<T>(NewArray<T>(length), length) { }
    ~ScopedVector() {
      DeleteArray(this->start());
    }
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ScopedVector);
  };
  
  #define STATIC_ASCII_VECTOR(x)                        \
    v8::internal::Vector<const uint8_t>(reinterpret_cast<const uint8_t*>(x), \
                                        ARRAY_SIZE(x)-1)
  
  inline Vector<const char> CStrVector(const char* data) {
    return Vector<const char>(data, StrLength(data));
  }
  
  inline Vector<const uint8_t> OneByteVector(const char* data, int length) {
    return Vector<const uint8_t>(reinterpret_cast<const uint8_t*>(data), length);
  }
  
  inline Vector<const uint8_t> OneByteVector(const char* data) {
    return OneByteVector(data, StrLength(data));
  }
  
  inline Vector<char> MutableCStrVector(char* data) {
    return Vector<char>(data, StrLength(data));
  }
  
  inline Vector<char> MutableCStrVector(char* data, int max) {
    int length = StrLength(data);
    return Vector<char>(data, (length < max) ? length : max);
  }
  
  
  /*
   * A class that collects values into a backing store.
   * Specialized versions of the class can allow access to the backing store
   * in different ways.
   * There is no guarantee that the backing store is contiguous (and, as a
   * consequence, no guarantees that consecutively added elements are adjacent
   * in memory). The collector may move elements unless it has guaranteed not
   * to.
   */
  template <typename T, int growth_factor = 2, int max_growth = 1 * MB>
  class Collector {
   public:
    explicit Collector(int initial_capacity = kMinCapacity)
        : index_(0), size_(0) {
      current_chunk_ = Vector<T>::New(initial_capacity);
    }
  
    virtual ~Collector() {
      // Free backing store (in reverse allocation order).
      current_chunk_.Dispose();
      for (int i = chunks_.length() - 1; i >= 0; i--) {
        chunks_.at(i).Dispose();
      }
    }
  
    // Add a single element.
    inline void Add(T value) {
      if (index_ >= current_chunk_.length()) {
        Grow(1);
      }
      current_chunk_[index_] = value;
      index_++;
      size_++;
    }
  
    // Add a block of contiguous elements and return a Vector backed by the
    // memory area.
    // A basic Collector will keep this vector valid as long as the Collector
    // is alive.
    inline Vector<T> AddBlock(int size, T initial_value) {
      ASSERT(size > 0);
      if (size > current_chunk_.length() - index_) {
        Grow(size);
      }
      T* position = current_chunk_.start() + index_;
      index_ += size;
      size_ += size;
      for (int i = 0; i < size; i++) {
        position[i] = initial_value;
      }
      return Vector<T>(position, size);
    }
  
  
    // Add a contiguous block of elements and return a vector backed
    // by the added block.
    // A basic Collector will keep this vector valid as long as the Collector
    // is alive.
    inline Vector<T> AddBlock(Vector<const T> source) {
      if (source.length() > current_chunk_.length() - index_) {
        Grow(source.length());
      }
      T* position = current_chunk_.start() + index_;
      index_ += source.length();
      size_ += source.length();
      for (int i = 0; i < source.length(); i++) {
        position[i] = source[i];
      }
      return Vector<T>(position, source.length());
    }
  
  
    // Write the contents of the collector into the provided vector.
    void WriteTo(Vector<T> destination) {
      ASSERT(size_ <= destination.length());
      int position = 0;
      for (int i = 0; i < chunks_.length(); i++) {
        Vector<T> chunk = chunks_.at(i);
        for (int j = 0; j < chunk.length(); j++) {
          destination[position] = chunk[j];
          position++;
        }
      }
      for (int i = 0; i < index_; i++) {
        destination[position] = current_chunk_[i];
        position++;
      }
    }
  
    // Allocate a single contiguous vector, copy all the collected
    // elements to the vector, and return it.
    // The caller is responsible for freeing the memory of the returned
    // vector (e.g., using Vector::Dispose).
    Vector<T> ToVector() {
      Vector<T> new_store = Vector<T>::New(size_);
      WriteTo(new_store);
      return new_store;
    }
  
    // Resets the collector to be empty.
    virtual void Reset();
  
    // Total number of elements added to collector so far.
    inline int size() { return size_; }
  
   protected:
    static const int kMinCapacity = 16;
    List<Vector<T> > chunks_;
    Vector<T> current_chunk_;  // Block of memory currently being written into.
    int index_;  // Current index in current chunk.
    int size_;  // Total number of elements in collector.
  
    // Creates a new current chunk, and stores the old chunk in the chunks_ list.
    void Grow(int min_capacity) {
      ASSERT(growth_factor > 1);
      int new_capacity;
      int current_length = current_chunk_.length();
      if (current_length < kMinCapacity) {
        // The collector started out as empty.
        new_capacity = min_capacity * growth_factor;
        if (new_capacity < kMinCapacity) new_capacity = kMinCapacity;
      } else {
        int growth = current_length * (growth_factor - 1);
        if (growth > max_growth) {
          growth = max_growth;
        }
        new_capacity = current_length + growth;
        if (new_capacity < min_capacity) {
          new_capacity = min_capacity + growth;
        }
      }
      NewChunk(new_capacity);
      ASSERT(index_ + min_capacity <= current_chunk_.length());
    }
  
    // Before replacing the current chunk, give a subclass the option to move
    // some of the current data into the new chunk. The function may update
    // the current index_ value to represent data no longer in the current chunk.
    // Returns the initial index of the new chunk (after copied data).
    virtual void NewChunk(int new_capacity)  {
      Vector<T> new_chunk = Vector<T>::New(new_capacity);
      if (index_ > 0) {
        chunks_.Add(current_chunk_.SubVector(0, index_));
      } else {
        current_chunk_.Dispose();
      }
      current_chunk_ = new_chunk;
      index_ = 0;
    }
  };
  
  
  /*
   * A collector that allows sequences of values to be guaranteed to
   * stay consecutive.
   * If the backing store grows while a sequence is active, the current
   * sequence might be moved, but after the sequence is ended, it will
   * not move again.
   * NOTICE: Blocks allocated using Collector::AddBlock(int) can move
   * as well, if inside an active sequence where another element is added.
   */
  template <typename T, int growth_factor = 2, int max_growth = 1 * MB>
  class SequenceCollector : public Collector<T, growth_factor, max_growth> {
   public:
    explicit SequenceCollector(int initial_capacity)
        : Collector<T, growth_factor, max_growth>(initial_capacity),
          sequence_start_(kNoSequence) { }
  
    virtual ~SequenceCollector() {}
  
    void StartSequence() {
      ASSERT(sequence_start_ == kNoSequence);
      sequence_start_ = this->index_;
    }
  
    Vector<T> EndSequence() {
      ASSERT(sequence_start_ != kNoSequence);
      int sequence_start = sequence_start_;
      sequence_start_ = kNoSequence;
      if (sequence_start == this->index_) return Vector<T>();
      return this->current_chunk_.SubVector(sequence_start, this->index_);
    }
  
    // Drops the currently added sequence, and all collected elements in it.
    void DropSequence() {
      ASSERT(sequence_start_ != kNoSequence);
      int sequence_length = this->index_ - sequence_start_;
      this->index_ = sequence_start_;
      this->size_ -= sequence_length;
      sequence_start_ = kNoSequence;
    }
  
    virtual void Reset() {
      sequence_start_ = kNoSequence;
      this->Collector<T, growth_factor, max_growth>::Reset();
    }
  
   private:
    static const int kNoSequence = -1;
    int sequence_start_;
  
    // Move the currently active sequence to the new chunk.
    virtual void NewChunk(int new_capacity) {
      if (sequence_start_ == kNoSequence) {
        // Fall back on default behavior if no sequence has been started.
        this->Collector<T, growth_factor, max_growth>::NewChunk(new_capacity);
        return;
      }
      int sequence_length = this->index_ - sequence_start_;
      Vector<T> new_chunk = Vector<T>::New(sequence_length + new_capacity);
      ASSERT(sequence_length < new_chunk.length());
      for (int i = 0; i < sequence_length; i++) {
        new_chunk[i] = this->current_chunk_[sequence_start_ + i];
      }
      if (sequence_start_ > 0) {
        this->chunks_.Add(this->current_chunk_.SubVector(0, sequence_start_));
      } else {
        this->current_chunk_.Dispose();
      }
      this->current_chunk_ = new_chunk;
      this->index_ = sequence_length;
      sequence_start_ = 0;
    }
  };
  
  
  // Compare ASCII/16bit chars to ASCII/16bit chars.
  template <typename lchar, typename rchar>
  inline int CompareCharsUnsigned(const lchar* lhs,
                                  const rchar* rhs,
                                  int chars) {
    const lchar* limit = lhs + chars;
  #ifdef V8_HOST_CAN_READ_UNALIGNED
    if (sizeof(*lhs) == sizeof(*rhs)) {
      // Number of characters in a uintptr_t.
      static const int kStepSize = sizeof(uintptr_t) / sizeof(*lhs);  // NOLINT
      while (lhs <= limit - kStepSize) {
        if (*reinterpret_cast<const uintptr_t*>(lhs) !=
            *reinterpret_cast<const uintptr_t*>(rhs)) {
          break;
        }
        lhs += kStepSize;
        rhs += kStepSize;
      }
    }
  #endif
    while (lhs < limit) {
      int r = static_cast<int>(*lhs) - static_cast<int>(*rhs);
      if (r != 0) return r;
      ++lhs;
      ++rhs;
    }
    return 0;
  }
  
  template<typename lchar, typename rchar>
  inline int CompareChars(const lchar* lhs, const rchar* rhs, int chars) {
    ASSERT(sizeof(lchar) <= 2);
    ASSERT(sizeof(rchar) <= 2);
    if (sizeof(lchar) == 1) {
      if (sizeof(rchar) == 1) {
        return CompareCharsUnsigned(reinterpret_cast<const uint8_t*>(lhs),
                                    reinterpret_cast<const uint8_t*>(rhs),
                                    chars);
      } else {
        return CompareCharsUnsigned(reinterpret_cast<const uint8_t*>(lhs),
                                    reinterpret_cast<const uint16_t*>(rhs),
                                    chars);
      }
    } else {
      if (sizeof(rchar) == 1) {
        return CompareCharsUnsigned(reinterpret_cast<const uint16_t*>(lhs),
                                    reinterpret_cast<const uint8_t*>(rhs),
                                    chars);
      } else {
        return CompareCharsUnsigned(reinterpret_cast<const uint16_t*>(lhs),
                                    reinterpret_cast<const uint16_t*>(rhs),
                                    chars);
      }
    }
  }
  
  
  // Calculate 10^exponent.
  inline int TenToThe(int exponent) {
    ASSERT(exponent <= 9);
    ASSERT(exponent >= 1);
    int answer = 10;
    for (int i = 1; i < exponent; i++) answer *= 10;
    return answer;
  }
  
  
  // The type-based aliasing rule allows the compiler to assume that pointers of
  // different types (for some definition of different) never alias each other.
  // Thus the following code does not work:
  //
  // float f = foo();
  // int fbits = *(int*)(&f);
  //
  // The compiler 'knows' that the int pointer can't refer to f since the types
  // don't match, so the compiler may cache f in a register, leaving random data
  // in fbits.  Using C++ style casts makes no difference, however a pointer to
  // char data is assumed to alias any other pointer.  This is the 'memcpy
  // exception'.
  //
  // Bit_cast uses the memcpy exception to move the bits from a variable of one
  // type of a variable of another type.  Of course the end result is likely to
  // be implementation dependent.  Most compilers (gcc-4.2 and MSVC 2005)
  // will completely optimize BitCast away.
  //
  // There is an additional use for BitCast.
  // Recent gccs will warn when they see casts that may result in breakage due to
  // the type-based aliasing rule.  If you have checked that there is no breakage
  // you can use BitCast to cast one pointer type to another.  This confuses gcc
  // enough that it can no longer see that you have cast one pointer type to
  // another thus avoiding the warning.
  
  // We need different implementations of BitCast for pointer and non-pointer
  // values. We use partial specialization of auxiliary struct to work around
  // issues with template functions overloading.
  template <class Dest, class Source>
  struct BitCastHelper {
    STATIC_ASSERT(sizeof(Dest) == sizeof(Source));
  
    INLINE(static Dest cast(const Source& source)) {
      Dest dest;
      // TODO(jkummerow): Refactor #includes and use OS::MemCopy() instead.
      memcpy(&dest, &source, sizeof(dest));
      return dest;
    }
  };
  
  template <class Dest, class Source>
  struct BitCastHelper<Dest, Source*> {
    INLINE(static Dest cast(Source* source)) {
      return BitCastHelper<Dest, uintptr_t>::
          cast(reinterpret_cast<uintptr_t>(source));
    }
  };
  
  template <class Dest, class Source>
  INLINE(Dest BitCast(const Source& source));
  
  template <class Dest, class Source>
  inline Dest BitCast(const Source& source) {
    return BitCastHelper<Dest, Source>::cast(source);
  }
  
  
  template<typename ElementType, int NumElements>
  class EmbeddedContainer {
   public:
    EmbeddedContainer() : elems_() { }
  
    int length() const { return NumElements; }
    const ElementType& operator[](int i) const {
      ASSERT(i < length());
      return elems_[i];
    }
    ElementType& operator[](int i) {
      ASSERT(i < length());
      return elems_[i];
    }
  
   private:
    ElementType elems_[NumElements];
  };
  
  
  template<typename ElementType>
  class EmbeddedContainer<ElementType, 0> {
   public:
    int length() const { return 0; }
    const ElementType& operator[](int i) const {
      UNREACHABLE();
      static ElementType t = 0;
      return t;
    }
    ElementType& operator[](int i) {
      UNREACHABLE();
      static ElementType t = 0;
      return t;
    }
  };
  
  
  // Helper class for building result strings in a character buffer. The
  // purpose of the class is to use safe operations that checks the
  // buffer bounds on all operations in debug mode.
  // This simple base class does not allow formatted output.
  class SimpleStringBuilder {
   public:
    // Create a string builder with a buffer of the given size. The
    // buffer is allocated through NewArray<char> and must be
    // deallocated by the caller of Finalize().
    explicit SimpleStringBuilder(int size);
  
    SimpleStringBuilder(char* buffer, int size)
        : buffer_(buffer, size), position_(0) { }
  
    ~SimpleStringBuilder() { if (!is_finalized()) Finalize(); }
  
    int size() const { return buffer_.length(); }
  
    // Get the current position in the builder.
    int position() const {
      ASSERT(!is_finalized());
      return position_;
    }
  
    // Reset the position.
    void Reset() { position_ = 0; }
  
    // Add a single character to the builder. It is not allowed to add
    // 0-characters; use the Finalize() method to terminate the string
    // instead.
    void AddCharacter(char c) {
      ASSERT(c != '\0');
      ASSERT(!is_finalized() && position_ < buffer_.length());
      buffer_[position_++] = c;
    }
  
    // Add an entire string to the builder. Uses strlen() internally to
    // compute the length of the input string.
    void AddString(const char* s);
  
    // Add the first 'n' characters of the given string 's' to the
    // builder. The input string must have enough characters.
    void AddSubstring(const char* s, int n);
  
    // Add character padding to the builder. If count is non-positive,
    // nothing is added to the builder.
    void AddPadding(char c, int count);
  
    // Add the decimal representation of the value.
    void AddDecimalInteger(int value);
  
    // Finalize the string by 0-terminating it and returning the buffer.
    char* Finalize();
  
   protected:
    Vector<char> buffer_;
    int position_;
  
    bool is_finalized() const { return position_ < 0; }
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(SimpleStringBuilder);
  };
  
  
  // A poor man's version of STL's bitset: A bit set of enums E (without explicit
  // values), fitting into an integral type T.
  template <class E, class T = int>
  class EnumSet {
   public:
    explicit EnumSet(T bits = 0) : bits_(bits) {}
    bool IsEmpty() const { return bits_ == 0; }
    bool Contains(E element) const { return (bits_ & Mask(element)) != 0; }
    bool ContainsAnyOf(const EnumSet& set) const {
      return (bits_ & set.bits_) != 0;
    }
    void Add(E element) { bits_ |= Mask(element); }
    void Add(const EnumSet& set) { bits_ |= set.bits_; }
    void Remove(E element) { bits_ &= ~Mask(element); }
    void Remove(const EnumSet& set) { bits_ &= ~set.bits_; }
    void RemoveAll() { bits_ = 0; }
    void Intersect(const EnumSet& set) { bits_ &= set.bits_; }
    T ToIntegral() const { return bits_; }
    bool operator==(const EnumSet& set) { return bits_ == set.bits_; }
    bool operator!=(const EnumSet& set) { return bits_ != set.bits_; }
    EnumSet<E, T> operator|(const EnumSet& set) const {
      return EnumSet<E, T>(bits_ | set.bits_);
    }
  
   private:
    T Mask(E element) const {
      // The strange typing in ASSERT is necessary to avoid stupid warnings, see:
      // http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43680
      ASSERT(static_cast<int>(element) < static_cast<int>(sizeof(T) * CHAR_BIT));
      return 1 << element;
    }
  
    T bits_;
  };
  
  
  class TypeFeedbackId {
   public:
    explicit TypeFeedbackId(int id) : id_(id) { }
    int ToInt() const { return id_; }
  
    static TypeFeedbackId None() { return TypeFeedbackId(kNoneId); }
    bool IsNone() const { return id_ == kNoneId; }
  
   private:
    static const int kNoneId = -1;
  
    int id_;
  };
  
  
  class BailoutId {
   public:
    explicit BailoutId(int id) : id_(id) { }
    int ToInt() const { return id_; }
  
    static BailoutId None() { return BailoutId(kNoneId); }
    static BailoutId FunctionEntry() { return BailoutId(kFunctionEntryId); }
    static BailoutId Declarations() { return BailoutId(kDeclarationsId); }
    static BailoutId FirstUsable() { return BailoutId(kFirstUsableId); }
    static BailoutId StubEntry() { return BailoutId(kStubEntryId); }
  
    bool IsNone() const { return id_ == kNoneId; }
    bool operator==(const BailoutId& other) const { return id_ == other.id_; }
  
   private:
    static const int kNoneId = -1;
  
    // Using 0 could disguise errors.
    static const int kFunctionEntryId = 2;
  
    // This AST id identifies the point after the declarations have been visited.
    // We need it to capture the environment effects of declarations that emit
    // code (function declarations).
    static const int kDeclarationsId = 3;
  
    // Every FunctionState starts with this id.
    static const int kFirstUsableId = 4;
  
    // Every compiled stub starts with this id.
    static const int kStubEntryId = 5;
  
    int id_;
  };
  
  } }  // namespace v8::internal
  
  #endif  // V8_UTILS_H_
  