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      1 //===- llvm/ADT/SmallVector.h - 'Normally small' vectors --------*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file defines the SmallVector class.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #ifndef LLVM_ADT_SMALLVECTOR_H
     15 #define LLVM_ADT_SMALLVECTOR_H
     16 
     17 #include "llvm/Support/type_traits.h"
     18 #include <algorithm>
     19 #include <cassert>
     20 #include <cstddef>
     21 #include <cstdlib>
     22 #include <cstring>
     23 #include <iterator>
     24 #include <memory>
     25 
     26 namespace llvm {
     27 
     28 /// SmallVectorBase - This is all the non-templated stuff common to all
     29 /// SmallVectors.
     30 class SmallVectorBase {
     31 protected:
     32   void *BeginX, *EndX, *CapacityX;
     33 
     34   // Allocate raw space for N elements of type T.  If T has a ctor or dtor, we
     35   // don't want it to be automatically run, so we need to represent the space as
     36   // something else.  An array of char would work great, but might not be
     37   // aligned sufficiently.  Instead we use some number of union instances for
     38   // the space, which guarantee maximal alignment.
     39   union U {
     40     double D;
     41     long double LD;
     42     long long L;
     43     void *P;
     44   } FirstEl;
     45   // Space after 'FirstEl' is clobbered, do not add any instance vars after it.
     46 
     47 protected:
     48   SmallVectorBase(size_t Size)
     49     : BeginX(&FirstEl), EndX(&FirstEl), CapacityX((char*)&FirstEl+Size) {}
     50 
     51   /// isSmall - Return true if this is a smallvector which has not had dynamic
     52   /// memory allocated for it.
     53   bool isSmall() const {
     54     return BeginX == static_cast<const void*>(&FirstEl);
     55   }
     56 
     57   /// grow_pod - This is an implementation of the grow() method which only works
     58   /// on POD-like data types and is out of line to reduce code duplication.
     59   void grow_pod(size_t MinSizeInBytes, size_t TSize);
     60 
     61 public:
     62   /// size_in_bytes - This returns size()*sizeof(T).
     63   size_t size_in_bytes() const {
     64     return size_t((char*)EndX - (char*)BeginX);
     65   }
     66 
     67   /// capacity_in_bytes - This returns capacity()*sizeof(T).
     68   size_t capacity_in_bytes() const {
     69     return size_t((char*)CapacityX - (char*)BeginX);
     70   }
     71 
     72   bool empty() const { return BeginX == EndX; }
     73 };
     74 
     75 
     76 template <typename T>
     77 class SmallVectorTemplateCommon : public SmallVectorBase {
     78 protected:
     79   SmallVectorTemplateCommon(size_t Size) : SmallVectorBase(Size) {}
     80 
     81   void setEnd(T *P) { this->EndX = P; }
     82 public:
     83   typedef size_t size_type;
     84   typedef ptrdiff_t difference_type;
     85   typedef T value_type;
     86   typedef T *iterator;
     87   typedef const T *const_iterator;
     88 
     89   typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
     90   typedef std::reverse_iterator<iterator> reverse_iterator;
     91 
     92   typedef T &reference;
     93   typedef const T &const_reference;
     94   typedef T *pointer;
     95   typedef const T *const_pointer;
     96 
     97   // forward iterator creation methods.
     98   iterator begin() { return (iterator)this->BeginX; }
     99   const_iterator begin() const { return (const_iterator)this->BeginX; }
    100   iterator end() { return (iterator)this->EndX; }
    101   const_iterator end() const { return (const_iterator)this->EndX; }
    102 protected:
    103   iterator capacity_ptr() { return (iterator)this->CapacityX; }
    104   const_iterator capacity_ptr() const { return (const_iterator)this->CapacityX;}
    105 public:
    106 
    107   // reverse iterator creation methods.
    108   reverse_iterator rbegin()            { return reverse_iterator(end()); }
    109   const_reverse_iterator rbegin() const{ return const_reverse_iterator(end()); }
    110   reverse_iterator rend()              { return reverse_iterator(begin()); }
    111   const_reverse_iterator rend() const { return const_reverse_iterator(begin());}
    112 
    113   size_type size() const { return end()-begin(); }
    114   size_type max_size() const { return size_type(-1) / sizeof(T); }
    115 
    116   /// capacity - Return the total number of elements in the currently allocated
    117   /// buffer.
    118   size_t capacity() const { return capacity_ptr() - begin(); }
    119 
    120   /// data - Return a pointer to the vector's buffer, even if empty().
    121   pointer data() { return pointer(begin()); }
    122   /// data - Return a pointer to the vector's buffer, even if empty().
    123   const_pointer data() const { return const_pointer(begin()); }
    124 
    125   reference operator[](unsigned idx) {
    126     assert(begin() + idx < end());
    127     return begin()[idx];
    128   }
    129   const_reference operator[](unsigned idx) const {
    130     assert(begin() + idx < end());
    131     return begin()[idx];
    132   }
    133 
    134   reference front() {
    135     return begin()[0];
    136   }
    137   const_reference front() const {
    138     return begin()[0];
    139   }
    140 
    141   reference back() {
    142     return end()[-1];
    143   }
    144   const_reference back() const {
    145     return end()[-1];
    146   }
    147 };
    148 
    149 /// SmallVectorTemplateBase<isPodLike = false> - This is where we put method
    150 /// implementations that are designed to work with non-POD-like T's.
    151 template <typename T, bool isPodLike>
    152 class SmallVectorTemplateBase : public SmallVectorTemplateCommon<T> {
    153 protected:
    154   SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}
    155 
    156   static void destroy_range(T *S, T *E) {
    157     while (S != E) {
    158       --E;
    159       E->~T();
    160     }
    161   }
    162 
    163   /// uninitialized_copy - Copy the range [I, E) onto the uninitialized memory
    164   /// starting with "Dest", constructing elements into it as needed.
    165   template<typename It1, typename It2>
    166   static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
    167     std::uninitialized_copy(I, E, Dest);
    168   }
    169 
    170   /// grow - double the size of the allocated memory, guaranteeing space for at
    171   /// least one more element or MinSize if specified.
    172   void grow(size_t MinSize = 0);
    173 
    174 public:
    175   void push_back(const T &Elt) {
    176     if (this->EndX < this->CapacityX) {
    177     Retry:
    178       new (this->end()) T(Elt);
    179       this->setEnd(this->end()+1);
    180       return;
    181     }
    182     this->grow();
    183     goto Retry;
    184   }
    185 
    186   void pop_back() {
    187     this->setEnd(this->end()-1);
    188     this->end()->~T();
    189   }
    190 };
    191 
    192 // Define this out-of-line to dissuade the C++ compiler from inlining it.
    193 template <typename T, bool isPodLike>
    194 void SmallVectorTemplateBase<T, isPodLike>::grow(size_t MinSize) {
    195   size_t CurCapacity = this->capacity();
    196   size_t CurSize = this->size();
    197   size_t NewCapacity = 2*CurCapacity + 1; // Always grow, even from zero.
    198   if (NewCapacity < MinSize)
    199     NewCapacity = MinSize;
    200   T *NewElts = static_cast<T*>(malloc(NewCapacity*sizeof(T)));
    201 
    202   // Copy the elements over.
    203   this->uninitialized_copy(this->begin(), this->end(), NewElts);
    204 
    205   // Destroy the original elements.
    206   destroy_range(this->begin(), this->end());
    207 
    208   // If this wasn't grown from the inline copy, deallocate the old space.
    209   if (!this->isSmall())
    210     free(this->begin());
    211 
    212   this->setEnd(NewElts+CurSize);
    213   this->BeginX = NewElts;
    214   this->CapacityX = this->begin()+NewCapacity;
    215 }
    216 
    217 
    218 /// SmallVectorTemplateBase<isPodLike = true> - This is where we put method
    219 /// implementations that are designed to work with POD-like T's.
    220 template <typename T>
    221 class SmallVectorTemplateBase<T, true> : public SmallVectorTemplateCommon<T> {
    222 protected:
    223   SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}
    224 
    225   // No need to do a destroy loop for POD's.
    226   static void destroy_range(T *, T *) {}
    227 
    228   /// uninitialized_copy - Copy the range [I, E) onto the uninitialized memory
    229   /// starting with "Dest", constructing elements into it as needed.
    230   template<typename It1, typename It2>
    231   static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
    232     // Arbitrary iterator types; just use the basic implementation.
    233     std::uninitialized_copy(I, E, Dest);
    234   }
    235 
    236   /// uninitialized_copy - Copy the range [I, E) onto the uninitialized memory
    237   /// starting with "Dest", constructing elements into it as needed.
    238   template<typename T1, typename T2>
    239   static void uninitialized_copy(T1 *I, T1 *E, T2 *Dest) {
    240     // Use memcpy for PODs iterated by pointers (which includes SmallVector
    241     // iterators): std::uninitialized_copy optimizes to memmove, but we can
    242     // use memcpy here.
    243     memcpy(Dest, I, (E-I)*sizeof(T));
    244   }
    245 
    246   /// grow - double the size of the allocated memory, guaranteeing space for at
    247   /// least one more element or MinSize if specified.
    248   void grow(size_t MinSize = 0) {
    249     this->grow_pod(MinSize*sizeof(T), sizeof(T));
    250   }
    251 public:
    252   void push_back(const T &Elt) {
    253     if (this->EndX < this->CapacityX) {
    254     Retry:
    255       *this->end() = Elt;
    256       this->setEnd(this->end()+1);
    257       return;
    258     }
    259     this->grow();
    260     goto Retry;
    261   }
    262 
    263   void pop_back() {
    264     this->setEnd(this->end()-1);
    265   }
    266 };
    267 
    268 
    269 /// SmallVectorImpl - This class consists of common code factored out of the
    270 /// SmallVector class to reduce code duplication based on the SmallVector 'N'
    271 /// template parameter.
    272 template <typename T>
    273 class SmallVectorImpl : public SmallVectorTemplateBase<T, isPodLike<T>::value> {
    274   typedef SmallVectorTemplateBase<T, isPodLike<T>::value > SuperClass;
    275 
    276   SmallVectorImpl(const SmallVectorImpl&); // DISABLED.
    277 public:
    278   typedef typename SuperClass::iterator iterator;
    279   typedef typename SuperClass::size_type size_type;
    280 
    281 protected:
    282   // Default ctor - Initialize to empty.
    283   explicit SmallVectorImpl(unsigned N)
    284     : SmallVectorTemplateBase<T, isPodLike<T>::value>(N*sizeof(T)) {
    285   }
    286 
    287 public:
    288   ~SmallVectorImpl() {
    289     // Destroy the constructed elements in the vector.
    290     this->destroy_range(this->begin(), this->end());
    291 
    292     // If this wasn't grown from the inline copy, deallocate the old space.
    293     if (!this->isSmall())
    294       free(this->begin());
    295   }
    296 
    297 
    298   void clear() {
    299     this->destroy_range(this->begin(), this->end());
    300     this->EndX = this->BeginX;
    301   }
    302 
    303   void resize(unsigned N) {
    304     if (N < this->size()) {
    305       this->destroy_range(this->begin()+N, this->end());
    306       this->setEnd(this->begin()+N);
    307     } else if (N > this->size()) {
    308       if (this->capacity() < N)
    309         this->grow(N);
    310       std::uninitialized_fill(this->end(), this->begin()+N, T());
    311       this->setEnd(this->begin()+N);
    312     }
    313   }
    314 
    315   void resize(unsigned N, const T &NV) {
    316     if (N < this->size()) {
    317       this->destroy_range(this->begin()+N, this->end());
    318       this->setEnd(this->begin()+N);
    319     } else if (N > this->size()) {
    320       if (this->capacity() < N)
    321         this->grow(N);
    322       std::uninitialized_fill(this->end(), this->begin()+N, NV);
    323       this->setEnd(this->begin()+N);
    324     }
    325   }
    326 
    327   void reserve(unsigned N) {
    328     if (this->capacity() < N)
    329       this->grow(N);
    330   }
    331 
    332   T pop_back_val() {
    333     T Result = this->back();
    334     this->pop_back();
    335     return Result;
    336   }
    337 
    338   void swap(SmallVectorImpl &RHS);
    339 
    340   /// append - Add the specified range to the end of the SmallVector.
    341   ///
    342   template<typename in_iter>
    343   void append(in_iter in_start, in_iter in_end) {
    344     size_type NumInputs = std::distance(in_start, in_end);
    345     // Grow allocated space if needed.
    346     if (NumInputs > size_type(this->capacity_ptr()-this->end()))
    347       this->grow(this->size()+NumInputs);
    348 
    349     // Copy the new elements over.
    350     // TODO: NEED To compile time dispatch on whether in_iter is a random access
    351     // iterator to use the fast uninitialized_copy.
    352     std::uninitialized_copy(in_start, in_end, this->end());
    353     this->setEnd(this->end() + NumInputs);
    354   }
    355 
    356   /// append - Add the specified range to the end of the SmallVector.
    357   ///
    358   void append(size_type NumInputs, const T &Elt) {
    359     // Grow allocated space if needed.
    360     if (NumInputs > size_type(this->capacity_ptr()-this->end()))
    361       this->grow(this->size()+NumInputs);
    362 
    363     // Copy the new elements over.
    364     std::uninitialized_fill_n(this->end(), NumInputs, Elt);
    365     this->setEnd(this->end() + NumInputs);
    366   }
    367 
    368   void assign(unsigned NumElts, const T &Elt) {
    369     clear();
    370     if (this->capacity() < NumElts)
    371       this->grow(NumElts);
    372     this->setEnd(this->begin()+NumElts);
    373     std::uninitialized_fill(this->begin(), this->end(), Elt);
    374   }
    375 
    376   iterator erase(iterator I) {
    377     iterator N = I;
    378     // Shift all elts down one.
    379     std::copy(I+1, this->end(), I);
    380     // Drop the last elt.
    381     this->pop_back();
    382     return(N);
    383   }
    384 
    385   iterator erase(iterator S, iterator E) {
    386     iterator N = S;
    387     // Shift all elts down.
    388     iterator I = std::copy(E, this->end(), S);
    389     // Drop the last elts.
    390     this->destroy_range(I, this->end());
    391     this->setEnd(I);
    392     return(N);
    393   }
    394 
    395   iterator insert(iterator I, const T &Elt) {
    396     if (I == this->end()) {  // Important special case for empty vector.
    397       this->push_back(Elt);
    398       return this->end()-1;
    399     }
    400 
    401     if (this->EndX < this->CapacityX) {
    402     Retry:
    403       new (this->end()) T(this->back());
    404       this->setEnd(this->end()+1);
    405       // Push everything else over.
    406       std::copy_backward(I, this->end()-1, this->end());
    407 
    408       // If we just moved the element we're inserting, be sure to update
    409       // the reference.
    410       const T *EltPtr = &Elt;
    411       if (I <= EltPtr && EltPtr < this->EndX)
    412         ++EltPtr;
    413 
    414       *I = *EltPtr;
    415       return I;
    416     }
    417     size_t EltNo = I-this->begin();
    418     this->grow();
    419     I = this->begin()+EltNo;
    420     goto Retry;
    421   }
    422 
    423   iterator insert(iterator I, size_type NumToInsert, const T &Elt) {
    424     if (I == this->end()) {  // Important special case for empty vector.
    425       append(NumToInsert, Elt);
    426       return this->end()-1;
    427     }
    428 
    429     // Convert iterator to elt# to avoid invalidating iterator when we reserve()
    430     size_t InsertElt = I - this->begin();
    431 
    432     // Ensure there is enough space.
    433     reserve(static_cast<unsigned>(this->size() + NumToInsert));
    434 
    435     // Uninvalidate the iterator.
    436     I = this->begin()+InsertElt;
    437 
    438     // If there are more elements between the insertion point and the end of the
    439     // range than there are being inserted, we can use a simple approach to
    440     // insertion.  Since we already reserved space, we know that this won't
    441     // reallocate the vector.
    442     if (size_t(this->end()-I) >= NumToInsert) {
    443       T *OldEnd = this->end();
    444       append(this->end()-NumToInsert, this->end());
    445 
    446       // Copy the existing elements that get replaced.
    447       std::copy_backward(I, OldEnd-NumToInsert, OldEnd);
    448 
    449       std::fill_n(I, NumToInsert, Elt);
    450       return I;
    451     }
    452 
    453     // Otherwise, we're inserting more elements than exist already, and we're
    454     // not inserting at the end.
    455 
    456     // Copy over the elements that we're about to overwrite.
    457     T *OldEnd = this->end();
    458     this->setEnd(this->end() + NumToInsert);
    459     size_t NumOverwritten = OldEnd-I;
    460     this->uninitialized_copy(I, OldEnd, this->end()-NumOverwritten);
    461 
    462     // Replace the overwritten part.
    463     std::fill_n(I, NumOverwritten, Elt);
    464 
    465     // Insert the non-overwritten middle part.
    466     std::uninitialized_fill_n(OldEnd, NumToInsert-NumOverwritten, Elt);
    467     return I;
    468   }
    469 
    470   template<typename ItTy>
    471   iterator insert(iterator I, ItTy From, ItTy To) {
    472     if (I == this->end()) {  // Important special case for empty vector.
    473       append(From, To);
    474       return this->end()-1;
    475     }
    476 
    477     size_t NumToInsert = std::distance(From, To);
    478     // Convert iterator to elt# to avoid invalidating iterator when we reserve()
    479     size_t InsertElt = I - this->begin();
    480 
    481     // Ensure there is enough space.
    482     reserve(static_cast<unsigned>(this->size() + NumToInsert));
    483 
    484     // Uninvalidate the iterator.
    485     I = this->begin()+InsertElt;
    486 
    487     // If there are more elements between the insertion point and the end of the
    488     // range than there are being inserted, we can use a simple approach to
    489     // insertion.  Since we already reserved space, we know that this won't
    490     // reallocate the vector.
    491     if (size_t(this->end()-I) >= NumToInsert) {
    492       T *OldEnd = this->end();
    493       append(this->end()-NumToInsert, this->end());
    494 
    495       // Copy the existing elements that get replaced.
    496       std::copy_backward(I, OldEnd-NumToInsert, OldEnd);
    497 
    498       std::copy(From, To, I);
    499       return I;
    500     }
    501 
    502     // Otherwise, we're inserting more elements than exist already, and we're
    503     // not inserting at the end.
    504 
    505     // Copy over the elements that we're about to overwrite.
    506     T *OldEnd = this->end();
    507     this->setEnd(this->end() + NumToInsert);
    508     size_t NumOverwritten = OldEnd-I;
    509     this->uninitialized_copy(I, OldEnd, this->end()-NumOverwritten);
    510 
    511     // Replace the overwritten part.
    512     for (; NumOverwritten > 0; --NumOverwritten) {
    513       *I = *From;
    514       ++I; ++From;
    515     }
    516 
    517     // Insert the non-overwritten middle part.
    518     this->uninitialized_copy(From, To, OldEnd);
    519     return I;
    520   }
    521 
    522   const SmallVectorImpl
    523   &operator=(const SmallVectorImpl &RHS);
    524 
    525   bool operator==(const SmallVectorImpl &RHS) const {
    526     if (this->size() != RHS.size()) return false;
    527     return std::equal(this->begin(), this->end(), RHS.begin());
    528   }
    529   bool operator!=(const SmallVectorImpl &RHS) const {
    530     return !(*this == RHS);
    531   }
    532 
    533   bool operator<(const SmallVectorImpl &RHS) const {
    534     return std::lexicographical_compare(this->begin(), this->end(),
    535                                         RHS.begin(), RHS.end());
    536   }
    537 
    538   /// set_size - Set the array size to \arg N, which the current array must have
    539   /// enough capacity for.
    540   ///
    541   /// This does not construct or destroy any elements in the vector.
    542   ///
    543   /// Clients can use this in conjunction with capacity() to write past the end
    544   /// of the buffer when they know that more elements are available, and only
    545   /// update the size later. This avoids the cost of value initializing elements
    546   /// which will only be overwritten.
    547   void set_size(unsigned N) {
    548     assert(N <= this->capacity());
    549     this->setEnd(this->begin() + N);
    550   }
    551 };
    552 
    553 
    554 template <typename T>
    555 void SmallVectorImpl<T>::swap(SmallVectorImpl<T> &RHS) {
    556   if (this == &RHS) return;
    557 
    558   // We can only avoid copying elements if neither vector is small.
    559   if (!this->isSmall() && !RHS.isSmall()) {
    560     std::swap(this->BeginX, RHS.BeginX);
    561     std::swap(this->EndX, RHS.EndX);
    562     std::swap(this->CapacityX, RHS.CapacityX);
    563     return;
    564   }
    565   if (RHS.size() > this->capacity())
    566     this->grow(RHS.size());
    567   if (this->size() > RHS.capacity())
    568     RHS.grow(this->size());
    569 
    570   // Swap the shared elements.
    571   size_t NumShared = this->size();
    572   if (NumShared > RHS.size()) NumShared = RHS.size();
    573   for (unsigned i = 0; i != static_cast<unsigned>(NumShared); ++i)
    574     std::swap((*this)[i], RHS[i]);
    575 
    576   // Copy over the extra elts.
    577   if (this->size() > RHS.size()) {
    578     size_t EltDiff = this->size() - RHS.size();
    579     this->uninitialized_copy(this->begin()+NumShared, this->end(), RHS.end());
    580     RHS.setEnd(RHS.end()+EltDiff);
    581     this->destroy_range(this->begin()+NumShared, this->end());
    582     this->setEnd(this->begin()+NumShared);
    583   } else if (RHS.size() > this->size()) {
    584     size_t EltDiff = RHS.size() - this->size();
    585     this->uninitialized_copy(RHS.begin()+NumShared, RHS.end(), this->end());
    586     this->setEnd(this->end() + EltDiff);
    587     this->destroy_range(RHS.begin()+NumShared, RHS.end());
    588     RHS.setEnd(RHS.begin()+NumShared);
    589   }
    590 }
    591 
    592 template <typename T>
    593 const SmallVectorImpl<T> &SmallVectorImpl<T>::
    594   operator=(const SmallVectorImpl<T> &RHS) {
    595   // Avoid self-assignment.
    596   if (this == &RHS) return *this;
    597 
    598   // If we already have sufficient space, assign the common elements, then
    599   // destroy any excess.
    600   size_t RHSSize = RHS.size();
    601   size_t CurSize = this->size();
    602   if (CurSize >= RHSSize) {
    603     // Assign common elements.
    604     iterator NewEnd;
    605     if (RHSSize)
    606       NewEnd = std::copy(RHS.begin(), RHS.begin()+RHSSize, this->begin());
    607     else
    608       NewEnd = this->begin();
    609 
    610     // Destroy excess elements.
    611     this->destroy_range(NewEnd, this->end());
    612 
    613     // Trim.
    614     this->setEnd(NewEnd);
    615     return *this;
    616   }
    617 
    618   // If we have to grow to have enough elements, destroy the current elements.
    619   // This allows us to avoid copying them during the grow.
    620   if (this->capacity() < RHSSize) {
    621     // Destroy current elements.
    622     this->destroy_range(this->begin(), this->end());
    623     this->setEnd(this->begin());
    624     CurSize = 0;
    625     this->grow(RHSSize);
    626   } else if (CurSize) {
    627     // Otherwise, use assignment for the already-constructed elements.
    628     std::copy(RHS.begin(), RHS.begin()+CurSize, this->begin());
    629   }
    630 
    631   // Copy construct the new elements in place.
    632   this->uninitialized_copy(RHS.begin()+CurSize, RHS.end(),
    633                            this->begin()+CurSize);
    634 
    635   // Set end.
    636   this->setEnd(this->begin()+RHSSize);
    637   return *this;
    638 }
    639 
    640 
    641 /// SmallVector - This is a 'vector' (really, a variable-sized array), optimized
    642 /// for the case when the array is small.  It contains some number of elements
    643 /// in-place, which allows it to avoid heap allocation when the actual number of
    644 /// elements is below that threshold.  This allows normal "small" cases to be
    645 /// fast without losing generality for large inputs.
    646 ///
    647 /// Note that this does not attempt to be exception safe.
    648 ///
    649 template <typename T, unsigned N>
    650 class SmallVector : public SmallVectorImpl<T> {
    651   /// InlineElts - These are 'N-1' elements that are stored inline in the body
    652   /// of the vector.  The extra '1' element is stored in SmallVectorImpl.
    653   typedef typename SmallVectorImpl<T>::U U;
    654   enum {
    655     // MinUs - The number of U's require to cover N T's.
    656     MinUs = (static_cast<unsigned int>(sizeof(T))*N +
    657              static_cast<unsigned int>(sizeof(U)) - 1) /
    658             static_cast<unsigned int>(sizeof(U)),
    659 
    660     // NumInlineEltsElts - The number of elements actually in this array.  There
    661     // is already one in the parent class, and we have to round up to avoid
    662     // having a zero-element array.
    663     NumInlineEltsElts = MinUs > 1 ? (MinUs - 1) : 1,
    664 
    665     // NumTsAvailable - The number of T's we actually have space for, which may
    666     // be more than N due to rounding.
    667     NumTsAvailable = (NumInlineEltsElts+1)*static_cast<unsigned int>(sizeof(U))/
    668                      static_cast<unsigned int>(sizeof(T))
    669   };
    670   U InlineElts[NumInlineEltsElts];
    671 public:
    672   SmallVector() : SmallVectorImpl<T>(NumTsAvailable) {
    673   }
    674 
    675   explicit SmallVector(unsigned Size, const T &Value = T())
    676     : SmallVectorImpl<T>(NumTsAvailable) {
    677     this->assign(Size, Value);
    678   }
    679 
    680   template<typename ItTy>
    681   SmallVector(ItTy S, ItTy E) : SmallVectorImpl<T>(NumTsAvailable) {
    682     this->append(S, E);
    683   }
    684 
    685   SmallVector(const SmallVector &RHS) : SmallVectorImpl<T>(NumTsAvailable) {
    686     if (!RHS.empty())
    687       SmallVectorImpl<T>::operator=(RHS);
    688   }
    689 
    690   const SmallVector &operator=(const SmallVector &RHS) {
    691     SmallVectorImpl<T>::operator=(RHS);
    692     return *this;
    693   }
    694 
    695 };
    696 
    697 /// Specialize SmallVector at N=0.  This specialization guarantees
    698 /// that it can be instantiated at an incomplete T if none of its
    699 /// members are required.
    700 template <typename T>
    701 class SmallVector<T,0> : public SmallVectorImpl<T> {
    702 public:
    703   SmallVector() : SmallVectorImpl<T>(0) {}
    704 
    705   explicit SmallVector(unsigned Size, const T &Value = T())
    706     : SmallVectorImpl<T>(0) {
    707     this->assign(Size, Value);
    708   }
    709 
    710   template<typename ItTy>
    711   SmallVector(ItTy S, ItTy E) : SmallVectorImpl<T>(0) {
    712     this->append(S, E);
    713   }
    714 
    715   SmallVector(const SmallVector &RHS) : SmallVectorImpl<T>(0) {
    716     SmallVectorImpl<T>::operator=(RHS);
    717   }
    718 
    719   SmallVector &operator=(const SmallVectorImpl<T> &RHS) {
    720     return SmallVectorImpl<T>::operator=(RHS);
    721   }
    722 
    723 };
    724 
    725 template<typename T, unsigned N>
    726 static inline size_t capacity_in_bytes(const SmallVector<T, N> &X) {
    727   return X.capacity_in_bytes();
    728 }
    729 
    730 } // End llvm namespace
    731 
    732 namespace std {
    733   /// Implement std::swap in terms of SmallVector swap.
    734   template<typename T>
    735   inline void
    736   swap(llvm::SmallVectorImpl<T> &LHS, llvm::SmallVectorImpl<T> &RHS) {
    737     LHS.swap(RHS);
    738   }
    739 
    740   /// Implement std::swap in terms of SmallVector swap.
    741   template<typename T, unsigned N>
    742   inline void
    743   swap(llvm::SmallVector<T, N> &LHS, llvm::SmallVector<T, N> &RHS) {
    744     LHS.swap(RHS);
    745   }
    746 }
    747 
    748 #endif
    749