text: // small vector modified from llvm
  
  #pragma once
  
  #include <algorithm>
  #include <cassert>
  #include <cstddef>
  #include <cstdlib>
  #include <cstring>
  #include <initializer_list>
  #include <iterator>
  #include <memory>
  
  #if defined(__GNUC__)
    #define TF_SMALLVEC_LIKELY(x) (__builtin_expect((x), 1))
    #define TF_SMALLVEC_UNLIKELY(x) (__builtin_expect((x), 0))
  #else
    #define TF_SMALLVEC_LIKELY(x) (x)
    #define TF_SMALLVEC_UNLIKELY(x) (x)
  #endif
  
  /** 
  @file small_vector.hpp
  @brief small vector include file
  */
  
  namespace tf { namespace detail {
  
  /**
  @private
  @brief NextCapacity - Returns the next power of two (in 64-bits)
         that is strictly greater than A.  Returns zero on overflow.
         this function assumes A to be positive
  */
  inline uint64_t NextCapacity(uint64_t A) {
    A |= (A >> 1);
    A |= (A >> 2);
    A |= (A >> 4);
    A |= (A >> 8);
    A |= (A >> 16);
    A |= (A >> 32);
    return A + 1;
  }
  
  }}  // end of namespace tf::detail --------------------------------------------
  
  
  namespace tf {
  
  /**
  @private
  */
  template <typename T>
  struct IsPod : std::integral_constant<bool, std::is_standard_layout<T>::value &&
                                              std::is_trivial<T>::value> {};
  
  /** 
  @private 
  */
  class SmallVectorBase {
  protected:
    void *BeginX, *EndX, *CapacityX;
  
  protected:
    SmallVectorBase(void *FirstEl, size_t Size)
      : BeginX(FirstEl), EndX(FirstEl), CapacityX((char*)FirstEl+Size) {}
  
    /// This is an implementation of the grow() method which only works
    /// on POD-like data types and is out of line to reduce code duplication.
    void grow_pod(void *FirstEl, size_t MinSizeInBytes, size_t TSize){
      size_t CurSizeBytes = size_in_bytes();
      size_t NewCapacityInBytes = 2 * capacity_in_bytes() + TSize; // Always grow.
      if (NewCapacityInBytes < MinSizeInBytes) {
        NewCapacityInBytes = MinSizeInBytes;
      }
  
      void *NewElts;
      if (BeginX == FirstEl) {
        NewElts = std::malloc(NewCapacityInBytes);
  
        // Copy the elements over.  No need to run dtors on PODs.
        memcpy(NewElts, this->BeginX, CurSizeBytes);
      } else {
        // If this wasn't grown from the inline copy, grow the allocated space.
        NewElts = realloc(this->BeginX, NewCapacityInBytes);
      }
      //assert(NewElts && "Out of memory");
  
      this->EndX = (char*)NewElts+CurSizeBytes;
      this->BeginX = NewElts;
      this->CapacityX = (char*)this->BeginX + NewCapacityInBytes;
    }
  
  public:
    /// This returns size()*sizeof(T).
    size_t size_in_bytes() const {
      return size_t((char*)EndX - (char*)BeginX);
    }
  
    /// capacity_in_bytes - This returns capacity()*sizeof(T).
    size_t capacity_in_bytes() const {
      return size_t((char*)CapacityX - (char*)BeginX);
    }
  
    bool empty() const { return BeginX == EndX; }
  };
  
  /**
  @private
  */
  template <typename T, unsigned N> struct SmallVectorStorage;
  
  /** 
  @private 
  */
  template <typename T, typename = void>
  class SmallVectorTemplateCommon : public SmallVectorBase {
  
    private:
    template <typename, unsigned> friend struct SmallVectorStorage;
  
    // Allocate raw space for N elements of type T.  If T has a ctor or dtor, we
    // don't want it to be automatically run, so we need to represent the space as
    // something else.  Use an array of char of sufficient alignment.
    ////////////typedef tf::AlignedCharArrayUnion<T> U;
    typedef typename std::aligned_union<1, T>::type U;
    U FirstEl;
    // Space after 'FirstEl' is clobbered, do not add any instance vars after it.
  
    protected:
    SmallVectorTemplateCommon(size_t Size) : SmallVectorBase(&FirstEl, Size) {}
  
    void grow_pod(size_t MinSizeInBytes, size_t TSize) {
      SmallVectorBase::grow_pod(&FirstEl, MinSizeInBytes, TSize);
    }
  
    /// Return true if this is a smallvector which has not had dynamic
    /// memory allocated for it.
    bool isSmall() const {
      return BeginX == static_cast<const void*>(&FirstEl);
    }
  
    /// Put this vector in a state of being small.
    void resetToSmall() {
      BeginX = EndX = CapacityX = &FirstEl;
    }
  
    void setEnd(T *P) { this->EndX = P; }
    
    public:
    typedef size_t size_type;
    typedef ptrdiff_t difference_type;
    typedef T value_type;
    typedef T *iterator;
    typedef const T *const_iterator;
  
    typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
    typedef std::reverse_iterator<iterator> reverse_iterator;
  
    typedef T &reference;
    typedef const T &const_reference;
    typedef T *pointer;
    typedef const T *const_pointer;
  
    // forward iterator creation methods.
    inline iterator begin() { return (iterator)this->BeginX; }
    inline const_iterator begin() const { return (const_iterator)this->BeginX; }
    inline iterator end() { return (iterator)this->EndX; }
    inline const_iterator end() const { return (const_iterator)this->EndX; }
  
    protected:
  
    iterator capacity_ptr() { return (iterator)this->CapacityX; }
    const_iterator capacity_ptr() const { return (const_iterator)this->CapacityX;}
    
    public:
  
    // reverse iterator creation methods.
    reverse_iterator rbegin()            { return reverse_iterator(end()); }
    const_reverse_iterator rbegin() const{ return const_reverse_iterator(end()); }
    reverse_iterator rend()              { return reverse_iterator(begin()); }
    const_reverse_iterator rend() const { return const_reverse_iterator(begin());}
  
    inline size_type size() const { return end()-begin(); }
    inline size_type max_size() const { return size_type(-1) / sizeof(T); }
  
    /// Return the total number of elements in the currently allocated buffer.
    size_t capacity() const { return capacity_ptr() - begin(); }
  
    /// Return a pointer to the vector's buffer, even if empty().
    pointer data() { return pointer(begin()); }
    /// Return a pointer to the vector's buffer, even if empty().
    const_pointer data() const { return const_pointer(begin()); }
  
    inline reference operator[](size_type idx) {
      //assert(idx < size());
      return begin()[idx];
    }
  
    inline const_reference operator[](size_type idx) const {
      //assert(idx < size());
      return begin()[idx];
    }
  
    reference front() {
      //assert(!empty());
      return begin()[0];
    }
  
    const_reference front() const {
      //assert(!empty());
      return begin()[0];
    }
  
    reference back() {
      //assert(!empty());
      return end()[-1];
    }
  
    const_reference back() const {
      //assert(!empty());
      return end()[-1];
    }
  };
  
  /**
  @private
  */
  template <typename T, bool isPodLike>
  class SmallVectorTemplateBase : public SmallVectorTemplateCommon<T> {
  
  protected:
    SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}
  
    static void destroy_range(T *S, T *E) {
      while (S != E) {
        --E;
        E->~T();
      }
    }
  
    /// Move the range [I, E) into the uninitialized memory starting with "Dest",
    /// constructing elements as needed.
    template<typename It1, typename It2>
    static void uninitialized_move(It1 I, It1 E, It2 Dest) {
      std::uninitialized_copy(std::make_move_iterator(I),
                              std::make_move_iterator(E), Dest);
    }
  
    /// Copy the range [I, E) onto the uninitialized memory starting with "Dest",
    /// constructing elements as needed.
    template<typename It1, typename It2>
    static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
      std::uninitialized_copy(I, E, Dest);
    }
  
    /// Grow the allocated memory (without initializing new elements), doubling
    /// the size of the allocated memory. Guarantees space for at least one more
    /// element, or MinSize more elements if specified.
    void grow(size_t MinSize = 0);
  
  public:
    void push_back(const T &Elt) {
      if (TF_SMALLVEC_UNLIKELY(this->EndX >= this->CapacityX))
        this->grow();
      ::new ((void*) this->end()) T(Elt);
      this->setEnd(this->end()+1);
    }
  
    void push_back(T &&Elt) {
      if (TF_SMALLVEC_UNLIKELY(this->EndX >= this->CapacityX))
        this->grow();
      ::new ((void*) this->end()) T(::std::move(Elt));
      this->setEnd(this->end()+1);
    }
  
    void pop_back() {
      this->setEnd(this->end()-1);
      this->end()->~T();
    }
  };
  
  /**
  @private
  */
  template <typename T, bool isPodLike>
  void SmallVectorTemplateBase<T, isPodLike>::grow(size_t MinSize) {
    size_t CurCapacity = this->capacity();
    size_t CurSize = this->size();
    // Always grow, even from zero.
    size_t NewCapacity = size_t(tf::detail::NextCapacity(CurCapacity+2));
    if (NewCapacity < MinSize)
      NewCapacity = MinSize;
    T *NewElts = static_cast<T*>(std::malloc(NewCapacity*sizeof(T)));
  
    // Move the elements over.
    this->uninitialized_move(this->begin(), this->end(), NewElts);
  
    // Destroy the original elements.
    destroy_range(this->begin(), this->end());
  
    // If this wasn't grown from the inline copy, deallocate the old space.
    if (!this->isSmall())
      std::free(this->begin());
  
    this->setEnd(NewElts+CurSize);
    this->BeginX = NewElts;
    this->CapacityX = this->begin()+NewCapacity;
  }
  
  /**
  @private
  */
  template <typename T>
  class SmallVectorTemplateBase<T, true> : public SmallVectorTemplateCommon<T> {
  protected:
    SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}
  
    // No need to do a destroy loop for POD's.
    static void destroy_range(T *, T *) {}
  
    /// Move the range [I, E) onto the uninitialized memory
    /// starting with "Dest", constructing elements into it as needed.
    template<typename It1, typename It2>
    static void uninitialized_move(It1 I, It1 E, It2 Dest) {
      // Just do a copy.
      uninitialized_copy(I, E, Dest);
    }
  
    /// Copy the range [I, E) onto the uninitialized memory
    /// starting with "Dest", constructing elements into it as needed.
    template<typename It1, typename It2>
    static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
      // Arbitrary iterator types; just use the basic implementation.
      std::uninitialized_copy(I, E, Dest);
    }
  
    /// Copy the range [I, E) onto the uninitialized memory
    /// starting with "Dest", constructing elements into it as needed.
    template <typename T1, typename T2>
    static void uninitialized_copy(
        T1 *I, T1 *E, T2 *Dest,
        typename std::enable_if<std::is_same<typename std::remove_const<T1>::type,
                                             T2>::value>::type * = nullptr) {
      // Use memcpy for PODs iterated by pointers (which includes SmallVector
      // iterators): std::uninitialized_copy optimizes to memmove, but we can
      // use memcpy here. Note that I and E are iterators and thus might be
      // invalid for memcpy if they are equal.
      if (I != E)
        memcpy(Dest, I, (E - I) * sizeof(T));
    }
  
    /// Double the size of the allocated memory, guaranteeing space for at
    /// least one more element or MinSize if specified.
    void grow(size_t MinSize = 0) {
      this->grow_pod(MinSize*sizeof(T), sizeof(T));
    }
  public:
    void push_back(const T &Elt) {
      if (TF_SMALLVEC_UNLIKELY(this->EndX >= this->CapacityX))
        this->grow();
      memcpy(this->end(), &Elt, sizeof(T));
      this->setEnd(this->end()+1);
    }
  
    void pop_back() {
      this->setEnd(this->end()-1);
    }
  };
  
  /** 
  @private
  */
  template <typename T>
  class SmallVectorImpl : public SmallVectorTemplateBase<T, IsPod<T>::value> {
    typedef SmallVectorTemplateBase<T, IsPod<T>::value> SuperClass;
  
    SmallVectorImpl(const SmallVectorImpl&) = delete;
  
  public:
    typedef typename SuperClass::iterator iterator;
    typedef typename SuperClass::const_iterator const_iterator;
    typedef typename SuperClass::size_type size_type;
  
  protected:
    // Default ctor - Initialize to empty.
    explicit SmallVectorImpl(unsigned N)
      : SmallVectorTemplateBase<T, IsPod<T>::value>(N*sizeof(T)) {
    }
  
  public:
    ~SmallVectorImpl() {
      // Destroy the constructed elements in the vector.
      this->destroy_range(this->begin(), this->end());
  
      // If this wasn't grown from the inline copy, deallocate the old space.
      if (!this->isSmall())
        std::free(this->begin());
    }
  
  
    void clear() {
      this->destroy_range(this->begin(), this->end());
      this->EndX = this->BeginX;
    }
  
    void resize(size_type N) {
      if (N < this->size()) {
        this->destroy_range(this->begin()+N, this->end());
        this->setEnd(this->begin()+N);
      } else if (N > this->size()) {
        if (this->capacity() < N)
          this->grow(N);
        for (auto I = this->end(), E = this->begin() + N; I != E; ++I)
          new (&*I) T();
        this->setEnd(this->begin()+N);
      }
    }
  
    void resize(size_type N, const T &NV) {
      if (N < this->size()) {
        this->destroy_range(this->begin()+N, this->end());
        this->setEnd(this->begin()+N);
      } else if (N > this->size()) {
        if (this->capacity() < N)
          this->grow(N);
        std::uninitialized_fill(this->end(), this->begin()+N, NV);
        this->setEnd(this->begin()+N);
      }
    }
  
    void reserve(size_type N) {
      if (this->capacity() < N)
        this->grow(N);
    }
  
    T pop_back_val() {
      T Result = ::std::move(this->back());
      this->pop_back();
      return Result;
    }
  
    void swap(SmallVectorImpl &RHS);
  
    /// Add the specified range to the end of the SmallVector.
    template<typename in_iter>
    void append(in_iter in_start, in_iter in_end) {
      size_type NumInputs = std::distance(in_start, in_end);
      // Grow allocated space if needed.
      if (NumInputs > size_type(this->capacity_ptr()-this->end()))
        this->grow(this->size()+NumInputs);
  
      // Copy the new elements over.
      this->uninitialized_copy(in_start, in_end, this->end());
      this->setEnd(this->end() + NumInputs);
    }
  
    /// Add the specified range to the end of the SmallVector.
    void append(size_type NumInputs, const T &Elt) {
      // Grow allocated space if needed.
      if (NumInputs > size_type(this->capacity_ptr()-this->end()))
        this->grow(this->size()+NumInputs);
  
      // Copy the new elements over.
      std::uninitialized_fill_n(this->end(), NumInputs, Elt);
      this->setEnd(this->end() + NumInputs);
    }
  
    void append(std::initializer_list<T> IL) {
      append(IL.begin(), IL.end());
    }
  
    void assign(size_type NumElts, const T &Elt) {
      clear();
      if (this->capacity() < NumElts)
        this->grow(NumElts);
      this->setEnd(this->begin()+NumElts);
      std::uninitialized_fill(this->begin(), this->end(), Elt);
    }
  
    void assign(std::initializer_list<T> IL) {
      clear();
      append(IL);
    }
  
    iterator erase(const_iterator CI) {
      // Just cast away constness because this is a non-const member function.
      iterator I = const_cast<iterator>(CI);
  
      //assert(I >= this->begin() && "Iterator to erase is out of bounds.");
      //assert(I < this->end() && "Erasing at past-the-end iterator.");
  
      iterator N = I;
      // Shift all elts down one.
      std::move(I+1, this->end(), I);
      // Drop the last elt.
      this->pop_back();
      return(N);
    }
  
    iterator erase(const_iterator CS, const_iterator CE) {
      // Just cast away constness because this is a non-const member function.
      iterator S = const_cast<iterator>(CS);
      iterator E = const_cast<iterator>(CE);
  
      //assert(S >= this->begin() && "Range to erase is out of bounds.");
      //assert(S <= E && "Trying to erase invalid range.");
      //assert(E <= this->end() && "Trying to erase past the end.");
  
      iterator N = S;
      // Shift all elts down.
      iterator I = std::move(E, this->end(), S);
      // Drop the last elts.
      this->destroy_range(I, this->end());
      this->setEnd(I);
      return(N);
    }
  
    iterator insert(iterator I, T &&Elt) {
      if (I == this->end()) {  // Important special case for empty vector.
        this->push_back(::std::move(Elt));
        return this->end()-1;
      }
  
      //assert(I >= this->begin() && "Insertion iterator is out of bounds.");
      //assert(I <= this->end() && "Inserting past the end of the vector.");
  
      if (this->EndX >= this->CapacityX) {
        size_t EltNo = I-this->begin();
        this->grow();
        I = this->begin()+EltNo;
      }
  
      ::new ((void*) this->end()) T(::std::move(this->back()));
      // Push everything else over.
      std::move_backward(I, this->end()-1, this->end());
      this->setEnd(this->end()+1);
  
      // If we just moved the element we're inserting, be sure to update
      // the reference.
      T *EltPtr = &Elt;
      if (I <= EltPtr && EltPtr < this->EndX)
        ++EltPtr;
  
      *I = ::std::move(*EltPtr);
      return I;
    }
  
    iterator insert(iterator I, const T &Elt) {
      if (I == this->end()) {  // Important special case for empty vector.
        this->push_back(Elt);
        return this->end()-1;
      }
  
      //assert(I >= this->begin() && "Insertion iterator is out of bounds.");
      //assert(I <= this->end() && "Inserting past the end of the vector.");
  
      if (this->EndX >= this->CapacityX) {
        size_t EltNo = I-this->begin();
        this->grow();
        I = this->begin()+EltNo;
      }
      ::new ((void*) this->end()) T(std::move(this->back()));
      // Push everything else over.
      std::move_backward(I, this->end()-1, this->end());
      this->setEnd(this->end()+1);
  
      // If we just moved the element we're inserting, be sure to update
      // the reference.
      const T *EltPtr = &Elt;
      if (I <= EltPtr && EltPtr < this->EndX)
        ++EltPtr;
  
      *I = *EltPtr;
      return I;
    }
  
    iterator insert(iterator I, size_type NumToInsert, const T &Elt) {
      // Convert iterator to elt# to avoid invalidating iterator when we reserve()
      size_t InsertElt = I - this->begin();
  
      if (I == this->end()) {  // Important special case for empty vector.
        append(NumToInsert, Elt);
        return this->begin()+InsertElt;
      }
  
      //assert(I >= this->begin() && "Insertion iterator is out of bounds.");
      //assert(I <= this->end() && "Inserting past the end of the vector.");
  
      // Ensure there is enough space.
      reserve(this->size() + NumToInsert);
  
      // Uninvalidate the iterator.
      I = this->begin()+InsertElt;
  
      // If there are more elements between the insertion point and the end of the
      // range than there are being inserted, we can use a simple approach to
      // insertion.  Since we already reserved space, we know that this won't
      // reallocate the vector.
      if (size_t(this->end()-I) >= NumToInsert) {
        T *OldEnd = this->end();
        append(std::move_iterator<iterator>(this->end() - NumToInsert),
               std::move_iterator<iterator>(this->end()));
  
        // Copy the existing elements that get replaced.
        std::move_backward(I, OldEnd-NumToInsert, OldEnd);
  
        std::fill_n(I, NumToInsert, Elt);
        return I;
      }
  
      // Otherwise, we're inserting more elements than exist already, and we're
      // not inserting at the end.
  
      // Move over the elements that we're about to overwrite.
      T *OldEnd = this->end();
      this->setEnd(this->end() + NumToInsert);
      size_t NumOverwritten = OldEnd-I;
      this->uninitialized_move(I, OldEnd, this->end()-NumOverwritten);
  
      // Replace the overwritten part.
      std::fill_n(I, NumOverwritten, Elt);
  
      // Insert the non-overwritten middle part.
      std::uninitialized_fill_n(OldEnd, NumToInsert-NumOverwritten, Elt);
      return I;
    }
  
    template<typename ItTy>
    iterator insert(iterator I, ItTy From, ItTy To) {
      // Convert iterator to elt# to avoid invalidating iterator when we reserve()
      size_t InsertElt = I - this->begin();
  
      if (I == this->end()) {  // Important special case for empty vector.
        append(From, To);
        return this->begin()+InsertElt;
      }
  
      //assert(I >= this->begin() && "Insertion iterator is out of bounds.");
      //assert(I <= this->end() && "Inserting past the end of the vector.");
  
      size_t NumToInsert = std::distance(From, To);
  
      // Ensure there is enough space.
      reserve(this->size() + NumToInsert);
  
      // Uninvalidate the iterator.
      I = this->begin()+InsertElt;
  
      // If there are more elements between the insertion point and the end of the
      // range than there are being inserted, we can use a simple approach to
      // insertion.  Since we already reserved space, we know that this won't
      // reallocate the vector.
      if (size_t(this->end()-I) >= NumToInsert) {
        T *OldEnd = this->end();
        append(std::move_iterator<iterator>(this->end() - NumToInsert),
               std::move_iterator<iterator>(this->end()));
  
        // Copy the existing elements that get replaced.
        std::move_backward(I, OldEnd-NumToInsert, OldEnd);
  
        std::copy(From, To, I);
        return I;
      }
  
      // Otherwise, we're inserting more elements than exist already, and we're
      // not inserting at the end.
  
      // Move over the elements that we're about to overwrite.
      T *OldEnd = this->end();
      this->setEnd(this->end() + NumToInsert);
      size_t NumOverwritten = OldEnd-I;
      this->uninitialized_move(I, OldEnd, this->end()-NumOverwritten);
  
      // Replace the overwritten part.
      for (T *J = I; NumOverwritten > 0; --NumOverwritten) {
        *J = *From;
        ++J; ++From;
      }
  
      // Insert the non-overwritten middle part.
      this->uninitialized_copy(From, To, OldEnd);
      return I;
    }
  
    void insert(iterator I, std::initializer_list<T> IL) {
      insert(I, IL.begin(), IL.end());
    }
  
    template <typename... ArgTypes> void emplace_back(ArgTypes &&... Args) {
      if (TF_SMALLVEC_UNLIKELY(this->EndX >= this->CapacityX))
        this->grow();
      ::new ((void *)this->end()) T(std::forward<ArgTypes>(Args)...);
      this->setEnd(this->end() + 1);
    }
  
    SmallVectorImpl &operator=(const SmallVectorImpl &RHS);
  
    SmallVectorImpl &operator=(SmallVectorImpl &&RHS);
  
    bool operator==(const SmallVectorImpl &RHS) const {
      if (this->size() != RHS.size()) return false;
      return std::equal(this->begin(), this->end(), RHS.begin());
    }
    bool operator!=(const SmallVectorImpl &RHS) const {
      return !(*this == RHS);
    }
  
    bool operator<(const SmallVectorImpl &RHS) const {
      return std::lexicographical_compare(this->begin(), this->end(),
                                          RHS.begin(), RHS.end());
    }
  
    /// Set the array size to \p N, which the current array must have enough
    /// capacity for.
    ///
    /// This does not construct or destroy any elements in the vector.
    ///
    /// Clients can use this in conjunction with capacity() to write past the end
    /// of the buffer when they know that more elements are available, and only
    /// update the size later. This avoids the cost of value initializing elements
    /// which will only be overwritten.
    void set_size(size_type N) {
      //assert(N <= this->capacity());
      this->setEnd(this->begin() + N);
    }
  };
  
  
  template <typename T>
  void SmallVectorImpl<T>::swap(SmallVectorImpl<T> &RHS) {
    if (this == &RHS) return;
  
    // We can only avoid copying elements if neither vector is small.
    if (!this->isSmall() && !RHS.isSmall()) {
      std::swap(this->BeginX, RHS.BeginX);
      std::swap(this->EndX, RHS.EndX);
      std::swap(this->CapacityX, RHS.CapacityX);
      return;
    }
    if (RHS.size() > this->capacity())
      this->grow(RHS.size());
    if (this->size() > RHS.capacity())
      RHS.grow(this->size());
  
    // Swap the shared elements.
    size_t NumShared = this->size();
    if (NumShared > RHS.size()) NumShared = RHS.size();
    for (size_type i = 0; i != NumShared; ++i)
      std::swap((*this)[i], RHS[i]);
  
    // Copy over the extra elts.
    if (this->size() > RHS.size()) {
      size_t EltDiff = this->size() - RHS.size();
      this->uninitialized_copy(this->begin()+NumShared, this->end(), RHS.end());
      RHS.setEnd(RHS.end()+EltDiff);
      this->destroy_range(this->begin()+NumShared, this->end());
      this->setEnd(this->begin()+NumShared);
    } else if (RHS.size() > this->size()) {
      size_t EltDiff = RHS.size() - this->size();
      this->uninitialized_copy(RHS.begin()+NumShared, RHS.end(), this->end());
      this->setEnd(this->end() + EltDiff);
      this->destroy_range(RHS.begin()+NumShared, RHS.end());
      RHS.setEnd(RHS.begin()+NumShared);
    }
  }
  
  template <typename T>
  SmallVectorImpl<T> &SmallVectorImpl<T>::
    operator=(const SmallVectorImpl<T> &RHS) {
    // Avoid self-assignment.
    if (this == &RHS) return *this;
  
    // If we already have sufficient space, assign the common elements, then
    // destroy any excess.
    size_t RHSSize = RHS.size();
    size_t CurSize = this->size();
    if (CurSize >= RHSSize) {
      // Assign common elements.
      iterator NewEnd;
      if (RHSSize)
        NewEnd = std::copy(RHS.begin(), RHS.begin()+RHSSize, this->begin());
      else
        NewEnd = this->begin();
  
      // Destroy excess elements.
      this->destroy_range(NewEnd, this->end());
  
      // Trim.
      this->setEnd(NewEnd);
      return *this;
    }
  
    // If we have to grow to have enough elements, destroy the current elements.
    // This allows us to avoid copying them during the grow.
    // FIXME: don't do this if they're efficiently moveable.
    if (this->capacity() < RHSSize) {
      // Destroy current elements.
      this->destroy_range(this->begin(), this->end());
      this->setEnd(this->begin());
      CurSize = 0;
      this->grow(RHSSize);
    } else if (CurSize) {
      // Otherwise, use assignment for the already-constructed elements.
      std::copy(RHS.begin(), RHS.begin()+CurSize, this->begin());
    }
  
    // Copy construct the new elements in place.
    this->uninitialized_copy(RHS.begin()+CurSize, RHS.end(),
                             this->begin()+CurSize);
  
    // Set end.
    this->setEnd(this->begin()+RHSSize);
    return *this;
  }
  
  template <typename T>
  SmallVectorImpl<T> &SmallVectorImpl<T>::operator=(SmallVectorImpl<T> &&RHS) {
    // Avoid self-assignment.
    if (this == &RHS) return *this;
  
    // If the RHS isn't small, clear this vector and then steal its buffer.
    if (!RHS.isSmall()) {
      this->destroy_range(this->begin(), this->end());
      if (!this->isSmall()) std::free(this->begin());
      this->BeginX = RHS.BeginX;
      this->EndX = RHS.EndX;
      this->CapacityX = RHS.CapacityX;
      RHS.resetToSmall();
      return *this;
    }
  
    // If we already have sufficient space, assign the common elements, then
    // destroy any excess.
    size_t RHSSize = RHS.size();
    size_t CurSize = this->size();
    if (CurSize >= RHSSize) {
      // Assign common elements.
      iterator NewEnd = this->begin();
      if (RHSSize)
        NewEnd = std::move(RHS.begin(), RHS.end(), NewEnd);
  
      // Destroy excess elements and trim the bounds.
      this->destroy_range(NewEnd, this->end());
      this->setEnd(NewEnd);
  
      // Clear the RHS.
      RHS.clear();
  
      return *this;
    }
  
    // If we have to grow to have enough elements, destroy the current elements.
    // This allows us to avoid copying them during the grow.
    // FIXME: this may not actually make any sense if we can efficiently move
    // elements.
    if (this->capacity() < RHSSize) {
      // Destroy current elements.
      this->destroy_range(this->begin(), this->end());
      this->setEnd(this->begin());
      CurSize = 0;
      this->grow(RHSSize);
    } else if (CurSize) {
      // Otherwise, use assignment for the already-constructed elements.
      std::move(RHS.begin(), RHS.begin()+CurSize, this->begin());
    }
  
    // Move-construct the new elements in place.
    this->uninitialized_move(RHS.begin()+CurSize, RHS.end(),
                             this->begin()+CurSize);
  
    // Set end.
    this->setEnd(this->begin()+RHSSize);
  
    RHS.clear();
    return *this;
  }
  
  /**
  @private
  */
  template <typename T, unsigned N>
  struct SmallVectorStorage {
    /**
    @private
    */
    typename SmallVectorTemplateCommon<T>::U InlineElts[N - 1];
  };
  
  /**
  @private
  */
  template <typename T> struct SmallVectorStorage<T, 1> {};
  
  /**
  @private
  */
  template <typename T> struct SmallVectorStorage<T, 0> {};
  
  /**
  @brief class to define a vector optimized for small array
  
  @tparam T data type
  @tparam N threshold of the number of elements in the initial storage
  
  The class defines a C++ STL-styled vector (a variable-sized array)
  optimized for the case when the array is small.
  It contains some number of elements in-place, 
  which allows it to avoid heap allocation when the actual number of
  elements is below that threshold. This allows normal @em small cases to be
  fast without losing generality for large inputs.
  All the methods in [std::vector](https://en.cppreference.com/w/cpp/container/vector)
  can apply to this class.
  
  The class is stripped from the LLVM codebase. 
  */
  template <typename T, unsigned N = 2>
  class SmallVector : public SmallVectorImpl<T> {
    /// Inline space for elements which aren't stored in the base class.
    SmallVectorStorage<T, N> Storage;
  
  public:
  
    /**
    @brief constructs an empty vector
    */
    SmallVector() : SmallVectorImpl<T>(N) {
    }
    
    /**
    @brief constructs a vector with @c Size copies of elements with value @c value
    */
    explicit SmallVector(size_t Size, const T &Value = T())
      : SmallVectorImpl<T>(N) {
      this->assign(Size, Value);
    }
    
    /**
    @brief constructs a vector with the contents of the range 
           <tt>[S, E)</tt>
     */
    template<typename ItTy>
    SmallVector(ItTy S, ItTy E) : SmallVectorImpl<T>(N) {
      this->append(S, E);
    }
  
    //template <typename RangeTy>
    //explicit SmallVector(const tf::iterator_range<RangeTy> &R)
    //    : SmallVectorImpl<T>(N) {
    //  this->append(R.begin(), R.end());
    //}
    
    /**
    @brief constructs a vector with the contents of the initializer list @c IL
    */
    SmallVector(std::initializer_list<T> IL) : SmallVectorImpl<T>(N) {
      this->assign(IL);
    }
    
    /**
    @brief constructs the vector with the copy of the contents of @c RHS
    */
    SmallVector(const SmallVector &RHS) : SmallVectorImpl<T>(N) {
      if (!RHS.empty())
        SmallVectorImpl<T>::operator=(RHS);
    }
    
    /**
    @brief constructs the vector with the contents of @c RHS using move semantics
    */
    SmallVector(SmallVector &&RHS) : SmallVectorImpl<T>(N) {
      if (!RHS.empty())
        SmallVectorImpl<T>::operator=(::std::move(RHS));
    }
    
    /**
    @brief replaces the contents with a copy of the contents of @c RHS
    */
    const SmallVector &operator=(const SmallVector &RHS) {
      SmallVectorImpl<T>::operator=(RHS);
      return *this;
    }
    
    /**
    @brief replaces the contents with the contents of @c RHS using move semantics
    */
    const SmallVector &operator=(SmallVector &&RHS) {
      SmallVectorImpl<T>::operator=(::std::move(RHS));
      return *this;
    }
    
    /**
    @brief constructs a vector with the contents of @c RHS using move semantics
    */
    SmallVector(SmallVectorImpl<T> &&RHS) : SmallVectorImpl<T>(N) {
      if (!RHS.empty())
        SmallVectorImpl<T>::operator=(::std::move(RHS));
    }
    
    /**
    @brief replaces the contents with the contents of @c RHS using move semantics
     */
    const SmallVector &operator=(SmallVectorImpl<T> &&RHS) {
      SmallVectorImpl<T>::operator=(::std::move(RHS));
      return *this;
    }
    
    /**
    @brief replaces the contents with the copy of the contents of an initializer list @c IL
     */
    const SmallVector &operator=(std::initializer_list<T> IL) {
      this->assign(IL);
      return *this;
    }
  };
  
  template<typename T, unsigned N>
  static inline size_t capacity_in_bytes(const SmallVector<T, N> &X) {
    return X.capacity_in_bytes();
  }
  
  } // end tf namespace ---------------------------------------------------------
  
  namespace std {
    /// Implement std::swap in terms of SmallVector swap.
    template<typename T>
    inline void
    swap(tf::SmallVectorImpl<T> &LHS, tf::SmallVectorImpl<T> &RHS) {
      LHS.swap(RHS);
    }
  
    /// Implement std::swap in terms of SmallVector swap.
    template<typename T, unsigned N>
    inline void
    swap(tf::SmallVector<T, N> &LHS, tf::SmallVector<T, N> &RHS) {
      LHS.swap(RHS);
    }
  }  // end of namespace std ----------------------------------------------------
  
  
  