text: //===- llvm/ADT/SmallPtrSet.h - 'Normally small' pointer set ----*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file defines the SmallPtrSet class.  See the doxygen comment for
  // SmallPtrSetImplBase for more details on the algorithm used.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_ADT_SMALLPTRSET_H
  #define LLVM_ADT_SMALLPTRSET_H
  
  #include "llvm/Compiler.h"
  #include "llvm/PointerLikeTypeTraits.h"
  #include <cassert>
  #include <cstddef>
  #include <cstdint>
  #include <cstring>
  #include <cstdlib>
  #include <iterator>
  #include <utility>
  
  namespace llvm {
  
  class SmallPtrSetIteratorImpl;
  
  /// SmallPtrSetImplBase - This is the common code shared among all the
  /// SmallPtrSet<>'s, which is almost everything.  SmallPtrSet has two modes, one
  /// for small and one for large sets.
  ///
  /// Small sets use an array of pointers allocated in the SmallPtrSet object,
  /// which is treated as a simple array of pointers.  When a pointer is added to
  /// the set, the array is scanned to see if the element already exists, if not
  /// the element is 'pushed back' onto the array.  If we run out of space in the
  /// array, we grow into the 'large set' case.  SmallSet should be used when the
  /// sets are often small.  In this case, no memory allocation is used, and only
  /// light-weight and cache-efficient scanning is used.
  ///
  /// Large sets use a classic exponentially-probed hash table.  Empty buckets are
  /// represented with an illegal pointer value (-1) to allow null pointers to be
  /// inserted.  Tombstones are represented with another illegal pointer value
  /// (-2), to allow deletion.  The hash table is resized when the table is 3/4 or
  /// more.  When this happens, the table is doubled in size.
  ///
  class SmallPtrSetImplBase {
    friend class SmallPtrSetIteratorImpl;
  
  protected:
    /// SmallArray - Points to a fixed size set of buckets, used in 'small mode'.
    const void **SmallArray;
    /// CurArray - This is the current set of buckets.  If equal to SmallArray,
    /// then the set is in 'small mode'.
    const void **CurArray;
    /// CurArraySize - The allocated size of CurArray, always a power of two.
    unsigned CurArraySize;
  
    /// Number of elements in CurArray that contain a value or are a tombstone.
    /// If small, all these elements are at the beginning of CurArray and the rest
    /// is uninitialized.
    unsigned NumNonEmpty;
    /// Number of tombstones in CurArray.
    unsigned NumTombstones;
  
    // Helpers to copy and move construct a SmallPtrSet.
    SmallPtrSetImplBase(const void **SmallStorage,
                        const SmallPtrSetImplBase &that);
    SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize,
                        SmallPtrSetImplBase &&that);
    explicit SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize)
        : SmallArray(SmallStorage), CurArray(SmallStorage),
          CurArraySize(SmallSize), NumNonEmpty(0), NumTombstones(0) {
      assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
             "Initial size must be a power of two!");
    }
    ~SmallPtrSetImplBase() {
      if (!isSmall())
        free(CurArray);
    }
  
  public:
    typedef unsigned size_type;
    bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const { return size() == 0; }
    size_type size() const { return NumNonEmpty - NumTombstones; }
  
    void clear() {
      // If the capacity of the array is huge, and the # elements used is small,
      // shrink the array.
      if (!isSmall()) {
        if (size() * 4 < CurArraySize && CurArraySize > 32)
          return shrink_and_clear();
        // Fill the array with empty markers.
        memset(CurArray, -1, CurArraySize * sizeof(void *));
      }
  
      NumNonEmpty = 0;
      NumTombstones = 0;
    }
  
  protected:
    static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
    static void *getEmptyMarker() {
      // Note that -1 is chosen to make clear() efficiently implementable with
      // memset and because it's not a valid pointer value.
      return reinterpret_cast<void*>(-1);
    }
  
    const void **EndPointer() const {
      return isSmall() ? CurArray + NumNonEmpty : CurArray + CurArraySize;
    }
  
    /// insert_imp - This returns true if the pointer was new to the set, false if
    /// it was already in the set.  This is hidden from the client so that the
    /// derived class can check that the right type of pointer is passed in.
    std::pair<const void *const *, bool> insert_imp(const void *Ptr) {
      if (isSmall()) {
        // Check to see if it is already in the set.
        const void **LastTombstone = nullptr;
        for (const void **APtr = SmallArray, **E = SmallArray + NumNonEmpty;
             APtr != E; ++APtr) {
          const void *Value = *APtr;
          if (Value == Ptr)
            return std::make_pair(APtr, false);
          if (Value == getTombstoneMarker())
            LastTombstone = APtr;
        }
  
        // Did we find any tombstone marker?
        if (LastTombstone != nullptr) {
          *LastTombstone = Ptr;
          --NumTombstones;
          return std::make_pair(LastTombstone, true);
        }
  
        // Nope, there isn't.  If we stay small, just 'pushback' now.
        if (NumNonEmpty < CurArraySize) {
          SmallArray[NumNonEmpty++] = Ptr;
          return std::make_pair(SmallArray + (NumNonEmpty - 1), true);
        }
        // Otherwise, hit the big set case, which will call grow.
      }
      return insert_imp_big(Ptr);
    }
  
    /// erase_imp - If the set contains the specified pointer, remove it and
    /// return true, otherwise return false.  This is hidden from the client so
    /// that the derived class can check that the right type of pointer is passed
    /// in.
    bool erase_imp(const void * Ptr);
  
    bool count_imp(const void * Ptr) const {
      if (isSmall()) {
        // Linear search for the item.
        for (const void *const *APtr = SmallArray,
                        *const *E = SmallArray + NumNonEmpty; APtr != E; ++APtr)
          if (*APtr == Ptr)
            return true;
        return false;
      }
  
      // Big set case.
      return *FindBucketFor(Ptr) == Ptr;
    }
  
  private:
    bool isSmall() const { return CurArray == SmallArray; }
  
    std::pair<const void *const *, bool> insert_imp_big(const void *Ptr);
  
    const void * const *FindBucketFor(const void *Ptr) const;
    void shrink_and_clear();
  
    /// Grow - Allocate a larger backing store for the buckets and move it over.
    void Grow(unsigned NewSize);
  
    void operator=(const SmallPtrSetImplBase &RHS) = delete;
  
  protected:
    /// swap - Swaps the elements of two sets.
    /// Note: This method assumes that both sets have the same small size.
    void swap(SmallPtrSetImplBase &RHS);
  
    void CopyFrom(const SmallPtrSetImplBase &RHS);
    void MoveFrom(unsigned SmallSize, SmallPtrSetImplBase &&RHS);
  
  private:
    /// Code shared by MoveFrom() and move constructor.
    void MoveHelper(unsigned SmallSize, SmallPtrSetImplBase &&RHS);
    /// Code shared by CopyFrom() and copy constructor.
    void CopyHelper(const SmallPtrSetImplBase &RHS);
  };
  
  /// SmallPtrSetIteratorImpl - This is the common base class shared between all
  /// instances of SmallPtrSetIterator.
  class SmallPtrSetIteratorImpl {
  protected:
    const void *const *Bucket;
    const void *const *End;
  
  public:
    explicit SmallPtrSetIteratorImpl(const void *const *BP, const void*const *E)
      : Bucket(BP), End(E) {
      AdvanceIfNotValid();
    }
  
    bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
      return Bucket == RHS.Bucket;
    }
    bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
      return Bucket != RHS.Bucket;
    }
  
  protected:
    /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket
    /// that is.   This is guaranteed to stop because the end() bucket is marked
    /// valid.
    void AdvanceIfNotValid() {
      assert(Bucket <= End);
      while (Bucket != End &&
             (*Bucket == SmallPtrSetImplBase::getEmptyMarker() ||
              *Bucket == SmallPtrSetImplBase::getTombstoneMarker()))
        ++Bucket;
    }
  };
  
  /// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
  template<typename PtrTy>
  class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
    typedef PointerLikeTypeTraits<PtrTy> PtrTraits;
  
  public:
    typedef PtrTy                     value_type;
    typedef PtrTy                     reference;
    typedef PtrTy                     pointer;
    typedef std::ptrdiff_t            difference_type;
    typedef std::forward_iterator_tag iterator_category;
  
    explicit SmallPtrSetIterator(const void *const *BP, const void *const *E)
      : SmallPtrSetIteratorImpl(BP, E) {}
  
    // Most methods provided by baseclass.
  
    const PtrTy operator*() const {
      assert(Bucket < End);
      return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket));
    }
  
    inline SmallPtrSetIterator& operator++() {          // Preincrement
      ++Bucket;
      AdvanceIfNotValid();
      return *this;
    }
  
    SmallPtrSetIterator operator++(int) {        // Postincrement
      SmallPtrSetIterator tmp = *this; ++*this; return tmp;
    }
  };
  
  /// RoundUpToPowerOfTwo - This is a helper template that rounds N up to the next
  /// power of two (which means N itself if N is already a power of two).
  template<unsigned N>
  struct RoundUpToPowerOfTwo;
  
  /// RoundUpToPowerOfTwoH - If N is not a power of two, increase it.  This is a
  /// helper template used to implement RoundUpToPowerOfTwo.
  template<unsigned N, bool isPowerTwo>
  struct RoundUpToPowerOfTwoH {
    enum { Val = N };
  };
  template<unsigned N>
  struct RoundUpToPowerOfTwoH<N, false> {
    enum {
      // We could just use NextVal = N+1, but this converges faster.  N|(N-1) sets
      // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
      Val = RoundUpToPowerOfTwo<(N|(N-1)) + 1>::Val
    };
  };
  
  template<unsigned N>
  struct RoundUpToPowerOfTwo {
    enum { Val = RoundUpToPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
  };
  
  /// \brief A templated base class for \c SmallPtrSet which provides the
  /// typesafe interface that is common across all small sizes.
  ///
  /// This is particularly useful for passing around between interface boundaries
  /// to avoid encoding a particular small size in the interface boundary.
  template <typename PtrType>
  class SmallPtrSetImpl : public SmallPtrSetImplBase {
    typedef PointerLikeTypeTraits<PtrType> PtrTraits;
  
    SmallPtrSetImpl(const SmallPtrSetImpl &) = delete;
  
  protected:
    // Constructors that forward to the base.
    SmallPtrSetImpl(const void **SmallStorage, const SmallPtrSetImpl &that)
        : SmallPtrSetImplBase(SmallStorage, that) {}
    SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize,
                    SmallPtrSetImpl &&that)
        : SmallPtrSetImplBase(SmallStorage, SmallSize, std::move(that)) {}
    explicit SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize)
        : SmallPtrSetImplBase(SmallStorage, SmallSize) {}
  
  public:
    typedef SmallPtrSetIterator<PtrType> iterator;
    typedef SmallPtrSetIterator<PtrType> const_iterator;
  
    /// Inserts Ptr if and only if there is no element in the container equal to
    /// Ptr. The bool component of the returned pair is true if and only if the
    /// insertion takes place, and the iterator component of the pair points to
    /// the element equal to Ptr.
    std::pair<iterator, bool> insert(PtrType Ptr) {
      auto p = insert_imp(PtrTraits::getAsVoidPointer(Ptr));
      return std::make_pair(iterator(p.first, EndPointer()), p.second);
    }
  
    /// erase - If the set contains the specified pointer, remove it and return
    /// true, otherwise return false.
    bool erase(PtrType Ptr) {
      return erase_imp(PtrTraits::getAsVoidPointer(Ptr));
    }
  
    /// count - Return 1 if the specified pointer is in the set, 0 otherwise.
    size_type count(PtrType Ptr) const {
      return count_imp(PtrTraits::getAsVoidPointer(Ptr)) ? 1 : 0;
    }
  
    template <typename IterT>
    void insert(IterT I, IterT E) {
      for (; I != E; ++I)
        insert(*I);
    }
  
    inline iterator begin() const {
      return iterator(CurArray, EndPointer());
    }
    inline iterator end() const {
      const void *const *End = EndPointer();
      return iterator(End, End);
    }
  };
  
  /// SmallPtrSet - This class implements a set which is optimized for holding
  /// SmallSize or less elements.  This internally rounds up SmallSize to the next
  /// power of two if it is not already a power of two.  See the comments above
  /// SmallPtrSetImplBase for details of the algorithm.
  template<class PtrType, unsigned SmallSize>
  class SmallPtrSet : public SmallPtrSetImpl<PtrType> {
    // In small mode SmallPtrSet uses linear search for the elements, so it is
    // not a good idea to choose this value too high. You may consider using a
    // DenseSet<> instead if you expect many elements in the set.
    static_assert(SmallSize <= 32, "SmallSize should be small");
  
    typedef SmallPtrSetImpl<PtrType> BaseT;
  
    // Make sure that SmallSize is a power of two, round up if not.
    enum { SmallSizePowTwo = RoundUpToPowerOfTwo<SmallSize>::Val };
    /// SmallStorage - Fixed size storage used in 'small mode'.
    const void *SmallStorage[SmallSizePowTwo];
  
  public:
    SmallPtrSet() : BaseT(SmallStorage, SmallSizePowTwo) {}
    SmallPtrSet(const SmallPtrSet &that) : BaseT(SmallStorage, that) {}
    SmallPtrSet(SmallPtrSet &&that)
        : BaseT(SmallStorage, SmallSizePowTwo, std::move(that)) {}
  
    template<typename It>
    SmallPtrSet(It I, It E) : BaseT(SmallStorage, SmallSizePowTwo) {
      this->insert(I, E);
    }
  
    SmallPtrSet<PtrType, SmallSize> &
    operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) {
      if (&RHS != this)
        this->CopyFrom(RHS);
      return *this;
    }
  
    SmallPtrSet<PtrType, SmallSize>&
    operator=(SmallPtrSet<PtrType, SmallSize> &&RHS) {
      if (&RHS != this)
        this->MoveFrom(SmallSizePowTwo, std::move(RHS));
      return *this;
    }
  
    /// swap - Swaps the elements of two sets.
    void swap(SmallPtrSet<PtrType, SmallSize> &RHS) {
      SmallPtrSetImplBase::swap(RHS);
    }
  };
  }
  
  namespace std {
    /// Implement std::swap in terms of SmallPtrSet swap.
    template<class T, unsigned N>
    inline void swap(llvm::SmallPtrSet<T, N> &LHS, llvm::SmallPtrSet<T, N> &RHS) {
      LHS.swap(RHS);
    }
  }
  
  #endif
  