text: //===- llvm/ADT/SparseBitVector.h - Efficient Sparse BitVector -*- 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 SparseBitVector class.  See the doxygen comment for
  // SparseBitVector for more details on the algorithm used.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_ADT_SPARSEBITVECTOR_H
  #define LLVM_ADT_SPARSEBITVECTOR_H
  
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/MathExtras.h"
  #include "llvm/Support/raw_ostream.h"
  #include <cassert>
  #include <climits>
  #include <cstring>
  #include <iterator>
  #include <list>
  
  namespace llvm {
  
  /// SparseBitVector is an implementation of a bitvector that is sparse by only
  /// storing the elements that have non-zero bits set.  In order to make this
  /// fast for the most common cases, SparseBitVector is implemented as a linked
  /// list of SparseBitVectorElements.  We maintain a pointer to the last
  /// SparseBitVectorElement accessed (in the form of a list iterator), in order
  /// to make multiple in-order test/set constant time after the first one is
  /// executed.  Note that using vectors to store SparseBitVectorElement's does
  /// not work out very well because it causes insertion in the middle to take
  /// enormous amounts of time with a large amount of bits.  Other structures that
  /// have better worst cases for insertion in the middle (various balanced trees,
  /// etc) do not perform as well in practice as a linked list with this iterator
  /// kept up to date.  They are also significantly more memory intensive.
  
  template <unsigned ElementSize = 128> struct SparseBitVectorElement {
  public:
    typedef unsigned long BitWord;
    typedef unsigned size_type;
    enum {
      BITWORD_SIZE = sizeof(BitWord) * CHAR_BIT,
      BITWORDS_PER_ELEMENT = (ElementSize + BITWORD_SIZE - 1) / BITWORD_SIZE,
      BITS_PER_ELEMENT = ElementSize
    };
  
  private:
    // Index of Element in terms of where first bit starts.
    unsigned ElementIndex;
    BitWord Bits[BITWORDS_PER_ELEMENT];
  
    SparseBitVectorElement() {
      ElementIndex = ~0U;
      memset(&Bits[0], 0, sizeof (BitWord) * BITWORDS_PER_ELEMENT);
    }
  
  public:
    explicit SparseBitVectorElement(unsigned Idx) {
      ElementIndex = Idx;
      memset(&Bits[0], 0, sizeof (BitWord) * BITWORDS_PER_ELEMENT);
    }
  
    // Comparison.
    bool operator==(const SparseBitVectorElement &RHS) const {
      if (ElementIndex != RHS.ElementIndex)
        return false;
      for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i)
        if (Bits[i] != RHS.Bits[i])
          return false;
      return true;
    }
  
    bool operator!=(const SparseBitVectorElement &RHS) const {
      return !(*this == RHS);
    }
  
    // Return the bits that make up word Idx in our element.
    BitWord word(unsigned Idx) const {
      assert(Idx < BITWORDS_PER_ELEMENT);
      return Bits[Idx];
    }
  
    unsigned index() const {
      return ElementIndex;
    }
  
    bool empty() const {
      for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i)
        if (Bits[i])
          return false;
      return true;
    }
  
    void set(unsigned Idx) {
      Bits[Idx / BITWORD_SIZE] |= 1L << (Idx % BITWORD_SIZE);
    }
  
    bool test_and_set (unsigned Idx) {
      bool old = test(Idx);
      if (!old) {
        set(Idx);
        return true;
      }
      return false;
    }
  
    void reset(unsigned Idx) {
      Bits[Idx / BITWORD_SIZE] &= ~(1L << (Idx % BITWORD_SIZE));
    }
  
    bool test(unsigned Idx) const {
      return Bits[Idx / BITWORD_SIZE] & (1L << (Idx % BITWORD_SIZE));
    }
  
    size_type count() const {
      unsigned NumBits = 0;
      for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i)
        NumBits += countPopulation(Bits[i]);
      return NumBits;
    }
  
    /// find_first - Returns the index of the first set bit.
    int find_first() const {
      for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i)
        if (Bits[i] != 0)
          return i * BITWORD_SIZE + countTrailingZeros(Bits[i]);
      llvm_unreachable("Illegal empty element");
    }
  
    /// find_last - Returns the index of the last set bit.
    int find_last() const {
      for (unsigned I = 0; I < BITWORDS_PER_ELEMENT; ++I) {
        unsigned Idx = BITWORDS_PER_ELEMENT - I - 1;
        if (Bits[Idx] != 0)
          return Idx * BITWORD_SIZE + BITWORD_SIZE -
                 countLeadingZeros(Bits[Idx]) - 1;
      }
      llvm_unreachable("Illegal empty element");
    }
  
    /// find_next - Returns the index of the next set bit starting from the
    /// "Curr" bit. Returns -1 if the next set bit is not found.
    int find_next(unsigned Curr) const {
      if (Curr >= BITS_PER_ELEMENT)
        return -1;
  
      unsigned WordPos = Curr / BITWORD_SIZE;
      unsigned BitPos = Curr % BITWORD_SIZE;
      BitWord Copy = Bits[WordPos];
      assert(WordPos <= BITWORDS_PER_ELEMENT
             && "Word Position outside of element");
  
      // Mask off previous bits.
      Copy &= ~0UL << BitPos;
  
      if (Copy != 0)
        return WordPos * BITWORD_SIZE + countTrailingZeros(Copy);
  
      // Check subsequent words.
      for (unsigned i = WordPos+1; i < BITWORDS_PER_ELEMENT; ++i)
        if (Bits[i] != 0)
          return i * BITWORD_SIZE + countTrailingZeros(Bits[i]);
      return -1;
    }
  
    // Union this element with RHS and return true if this one changed.
    bool unionWith(const SparseBitVectorElement &RHS) {
      bool changed = false;
      for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i) {
        BitWord old = changed ? 0 : Bits[i];
  
        Bits[i] |= RHS.Bits[i];
        if (!changed && old != Bits[i])
          changed = true;
      }
      return changed;
    }
  
    // Return true if we have any bits in common with RHS
    bool intersects(const SparseBitVectorElement &RHS) const {
      for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i) {
        if (RHS.Bits[i] & Bits[i])
          return true;
      }
      return false;
    }
  
    // Intersect this Element with RHS and return true if this one changed.
    // BecameZero is set to true if this element became all-zero bits.
    bool intersectWith(const SparseBitVectorElement &RHS,
                       bool &BecameZero) {
      bool changed = false;
      bool allzero = true;
  
      BecameZero = false;
      for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i) {
        BitWord old = changed ? 0 : Bits[i];
  
        Bits[i] &= RHS.Bits[i];
        if (Bits[i] != 0)
          allzero = false;
  
        if (!changed && old != Bits[i])
          changed = true;
      }
      BecameZero = allzero;
      return changed;
    }
  
    // Intersect this Element with the complement of RHS and return true if this
    // one changed.  BecameZero is set to true if this element became all-zero
    // bits.
    bool intersectWithComplement(const SparseBitVectorElement &RHS,
                                 bool &BecameZero) {
      bool changed = false;
      bool allzero = true;
  
      BecameZero = false;
      for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i) {
        BitWord old = changed ? 0 : Bits[i];
  
        Bits[i] &= ~RHS.Bits[i];
        if (Bits[i] != 0)
          allzero = false;
  
        if (!changed && old != Bits[i])
          changed = true;
      }
      BecameZero = allzero;
      return changed;
    }
  
    // Three argument version of intersectWithComplement that intersects
    // RHS1 & ~RHS2 into this element
    void intersectWithComplement(const SparseBitVectorElement &RHS1,
                                 const SparseBitVectorElement &RHS2,
                                 bool &BecameZero) {
      bool allzero = true;
  
      BecameZero = false;
      for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i) {
        Bits[i] = RHS1.Bits[i] & ~RHS2.Bits[i];
        if (Bits[i] != 0)
          allzero = false;
      }
      BecameZero = allzero;
    }
  };
  
  template <unsigned ElementSize = 128>
  class SparseBitVector {
    typedef std::list<SparseBitVectorElement<ElementSize>> ElementList;
    typedef typename ElementList::iterator ElementListIter;
    typedef typename ElementList::const_iterator ElementListConstIter;
    enum {
      BITWORD_SIZE = SparseBitVectorElement<ElementSize>::BITWORD_SIZE
    };
  
    // Pointer to our current Element.
    ElementListIter CurrElementIter;
    ElementList Elements;
  
    // This is like std::lower_bound, except we do linear searching from the
    // current position.
    ElementListIter FindLowerBound(unsigned ElementIndex) {
  
      if (Elements.empty()) {
        CurrElementIter = Elements.begin();
        return Elements.begin();
      }
  
      // Make sure our current iterator is valid.
      if (CurrElementIter == Elements.end())
        --CurrElementIter;
  
      // Search from our current iterator, either backwards or forwards,
      // depending on what element we are looking for.
      ElementListIter ElementIter = CurrElementIter;
      if (CurrElementIter->index() == ElementIndex) {
        return ElementIter;
      } else if (CurrElementIter->index() > ElementIndex) {
        while (ElementIter != Elements.begin()
               && ElementIter->index() > ElementIndex)
          --ElementIter;
      } else {
        while (ElementIter != Elements.end() &&
               ElementIter->index() < ElementIndex)
          ++ElementIter;
      }
      CurrElementIter = ElementIter;
      return ElementIter;
    }
  
    // Iterator to walk set bits in the bitmap.  This iterator is a lot uglier
    // than it would be, in order to be efficient.
    class SparseBitVectorIterator {
    private:
      bool AtEnd;
  
      const SparseBitVector<ElementSize> *BitVector = nullptr;
  
      // Current element inside of bitmap.
      ElementListConstIter Iter;
  
      // Current bit number inside of our bitmap.
      unsigned BitNumber;
  
      // Current word number inside of our element.
      unsigned WordNumber;
  
      // Current bits from the element.
      typename SparseBitVectorElement<ElementSize>::BitWord Bits;
  
      // Move our iterator to the first non-zero bit in the bitmap.
      void AdvanceToFirstNonZero() {
        if (AtEnd)
          return;
        if (BitVector->Elements.empty()) {
          AtEnd = true;
          return;
        }
        Iter = BitVector->Elements.begin();
        BitNumber = Iter->index() * ElementSize;
        unsigned BitPos = Iter->find_first();
        BitNumber += BitPos;
        WordNumber = (BitNumber % ElementSize) / BITWORD_SIZE;
        Bits = Iter->word(WordNumber);
        Bits >>= BitPos % BITWORD_SIZE;
      }
  
      // Move our iterator to the next non-zero bit.
      void AdvanceToNextNonZero() {
        if (AtEnd)
          return;
  
        while (Bits && !(Bits & 1)) {
          Bits >>= 1;
          BitNumber += 1;
        }
  
        // See if we ran out of Bits in this word.
        if (!Bits) {
          int NextSetBitNumber = Iter->find_next(BitNumber % ElementSize) ;
          // If we ran out of set bits in this element, move to next element.
          if (NextSetBitNumber == -1 || (BitNumber % ElementSize == 0)) {
            ++Iter;
            WordNumber = 0;
  
            // We may run out of elements in the bitmap.
            if (Iter == BitVector->Elements.end()) {
              AtEnd = true;
              return;
            }
            // Set up for next non-zero word in bitmap.
            BitNumber = Iter->index() * ElementSize;
            NextSetBitNumber = Iter->find_first();
            BitNumber += NextSetBitNumber;
            WordNumber = (BitNumber % ElementSize) / BITWORD_SIZE;
            Bits = Iter->word(WordNumber);
            Bits >>= NextSetBitNumber % BITWORD_SIZE;
          } else {
            WordNumber = (NextSetBitNumber % ElementSize) / BITWORD_SIZE;
            Bits = Iter->word(WordNumber);
            Bits >>= NextSetBitNumber % BITWORD_SIZE;
            BitNumber = Iter->index() * ElementSize;
            BitNumber += NextSetBitNumber;
          }
        }
      }
  
    public:
      SparseBitVectorIterator() = default;
  
      SparseBitVectorIterator(const SparseBitVector<ElementSize> *RHS,
                              bool end = false):BitVector(RHS) {
        Iter = BitVector->Elements.begin();
        BitNumber = 0;
        Bits = 0;
        WordNumber = ~0;
        AtEnd = end;
        AdvanceToFirstNonZero();
      }
  
      // Preincrement.
      inline SparseBitVectorIterator& operator++() {
        ++BitNumber;
        Bits >>= 1;
        AdvanceToNextNonZero();
        return *this;
      }
  
      // Postincrement.
      inline SparseBitVectorIterator operator++(int) {
        SparseBitVectorIterator tmp = *this;
        ++*this;
        return tmp;
      }
  
      // Return the current set bit number.
      unsigned operator*() const {
        return BitNumber;
      }
  
      bool operator==(const SparseBitVectorIterator &RHS) const {
        // If they are both at the end, ignore the rest of the fields.
        if (AtEnd && RHS.AtEnd)
          return true;
        // Otherwise they are the same if they have the same bit number and
        // bitmap.
        return AtEnd == RHS.AtEnd && RHS.BitNumber == BitNumber;
      }
  
      bool operator!=(const SparseBitVectorIterator &RHS) const {
        return !(*this == RHS);
      }
    };
  
  public:
    typedef SparseBitVectorIterator iterator;
  
    SparseBitVector() {
      CurrElementIter = Elements.begin();
    }
  
    ~SparseBitVector() = default;
  
    // SparseBitVector copy ctor.
    SparseBitVector(const SparseBitVector &RHS) {
      ElementListConstIter ElementIter = RHS.Elements.begin();
      while (ElementIter != RHS.Elements.end()) {
        Elements.push_back(SparseBitVectorElement<ElementSize>(*ElementIter));
        ++ElementIter;
      }
  
      CurrElementIter = Elements.begin ();
    }
  
    // Clear.
    void clear() {
      Elements.clear();
    }
  
    // Assignment
    SparseBitVector& operator=(const SparseBitVector& RHS) {
      if (this == &RHS)
        return *this;
  
      Elements.clear();
  
      ElementListConstIter ElementIter = RHS.Elements.begin();
      while (ElementIter != RHS.Elements.end()) {
        Elements.push_back(SparseBitVectorElement<ElementSize>(*ElementIter));
        ++ElementIter;
      }
  
      CurrElementIter = Elements.begin ();
  
      return *this;
    }
  
    // Test, Reset, and Set a bit in the bitmap.
    bool test(unsigned Idx) {
      if (Elements.empty())
        return false;
  
      unsigned ElementIndex = Idx / ElementSize;
      ElementListIter ElementIter = FindLowerBound(ElementIndex);
  
      // If we can't find an element that is supposed to contain this bit, there
      // is nothing more to do.
      if (ElementIter == Elements.end() ||
          ElementIter->index() != ElementIndex)
        return false;
      return ElementIter->test(Idx % ElementSize);
    }
  
    void reset(unsigned Idx) {
      if (Elements.empty())
        return;
  
      unsigned ElementIndex = Idx / ElementSize;
      ElementListIter ElementIter = FindLowerBound(ElementIndex);
  
      // If we can't find an element that is supposed to contain this bit, there
      // is nothing more to do.
      if (ElementIter == Elements.end() ||
          ElementIter->index() != ElementIndex)
        return;
      ElementIter->reset(Idx % ElementSize);
  
      // When the element is zeroed out, delete it.
      if (ElementIter->empty()) {
        ++CurrElementIter;
        Elements.erase(ElementIter);
      }
    }
  
    void set(unsigned Idx) {
      unsigned ElementIndex = Idx / ElementSize;
      ElementListIter ElementIter;
      if (Elements.empty()) {
        ElementIter = Elements.emplace(Elements.end(), ElementIndex);
      } else {
        ElementIter = FindLowerBound(ElementIndex);
  
        if (ElementIter == Elements.end() ||
            ElementIter->index() != ElementIndex) {
          // We may have hit the beginning of our SparseBitVector, in which case,
          // we may need to insert right after this element, which requires moving
          // the current iterator forward one, because insert does insert before.
          if (ElementIter != Elements.end() &&
              ElementIter->index() < ElementIndex)
            ++ElementIter;
          ElementIter = Elements.emplace(ElementIter, ElementIndex);
        }
      }
      CurrElementIter = ElementIter;
  
      ElementIter->set(Idx % ElementSize);
    }
  
    bool test_and_set(unsigned Idx) {
      bool old = test(Idx);
      if (!old) {
        set(Idx);
        return true;
      }
      return false;
    }
  
    bool operator!=(const SparseBitVector &RHS) const {
      return !(*this == RHS);
    }
  
    bool operator==(const SparseBitVector &RHS) const {
      ElementListConstIter Iter1 = Elements.begin();
      ElementListConstIter Iter2 = RHS.Elements.begin();
  
      for (; Iter1 != Elements.end() && Iter2 != RHS.Elements.end();
           ++Iter1, ++Iter2) {
        if (*Iter1 != *Iter2)
          return false;
      }
      return Iter1 == Elements.end() && Iter2 == RHS.Elements.end();
    }
  
    // Union our bitmap with the RHS and return true if we changed.
    bool operator|=(const SparseBitVector &RHS) {
      if (this == &RHS)
        return false;
  
      bool changed = false;
      ElementListIter Iter1 = Elements.begin();
      ElementListConstIter Iter2 = RHS.Elements.begin();
  
      // If RHS is empty, we are done
      if (RHS.Elements.empty())
        return false;
  
      while (Iter2 != RHS.Elements.end()) {
        if (Iter1 == Elements.end() || Iter1->index() > Iter2->index()) {
          Elements.insert(Iter1, *Iter2);
          ++Iter2;
          changed = true;
        } else if (Iter1->index() == Iter2->index()) {
          changed |= Iter1->unionWith(*Iter2);
          ++Iter1;
          ++Iter2;
        } else {
          ++Iter1;
        }
      }
      CurrElementIter = Elements.begin();
      return changed;
    }
  
    // Intersect our bitmap with the RHS and return true if ours changed.
    bool operator&=(const SparseBitVector &RHS) {
      if (this == &RHS)
        return false;
  
      bool changed = false;
      ElementListIter Iter1 = Elements.begin();
      ElementListConstIter Iter2 = RHS.Elements.begin();
  
      // Check if both bitmaps are empty.
      if (Elements.empty() && RHS.Elements.empty())
        return false;
  
      // Loop through, intersecting as we go, erasing elements when necessary.
      while (Iter2 != RHS.Elements.end()) {
        if (Iter1 == Elements.end()) {
          CurrElementIter = Elements.begin();
          return changed;
        }
  
        if (Iter1->index() > Iter2->index()) {
          ++Iter2;
        } else if (Iter1->index() == Iter2->index()) {
          bool BecameZero;
          changed |= Iter1->intersectWith(*Iter2, BecameZero);
          if (BecameZero) {
            ElementListIter IterTmp = Iter1;
            ++Iter1;
            Elements.erase(IterTmp);
          } else {
            ++Iter1;
          }
          ++Iter2;
        } else {
          ElementListIter IterTmp = Iter1;
          ++Iter1;
          Elements.erase(IterTmp);
          changed = true;
        }
      }
      if (Iter1 != Elements.end()) {
        Elements.erase(Iter1, Elements.end());
        changed = true;
      }
      CurrElementIter = Elements.begin();
      return changed;
    }
  
    // Intersect our bitmap with the complement of the RHS and return true
    // if ours changed.
    bool intersectWithComplement(const SparseBitVector &RHS) {
      if (this == &RHS) {
        if (!empty()) {
          clear();
          return true;
        }
        return false;
      }
  
      bool changed = false;
      ElementListIter Iter1 = Elements.begin();
      ElementListConstIter Iter2 = RHS.Elements.begin();
  
      // If either our bitmap or RHS is empty, we are done
      if (Elements.empty() || RHS.Elements.empty())
        return false;
  
      // Loop through, intersecting as we go, erasing elements when necessary.
      while (Iter2 != RHS.Elements.end()) {
        if (Iter1 == Elements.end()) {
          CurrElementIter = Elements.begin();
          return changed;
        }
  
        if (Iter1->index() > Iter2->index()) {
          ++Iter2;
        } else if (Iter1->index() == Iter2->index()) {
          bool BecameZero;
          changed |= Iter1->intersectWithComplement(*Iter2, BecameZero);
          if (BecameZero) {
            ElementListIter IterTmp = Iter1;
            ++Iter1;
            Elements.erase(IterTmp);
          } else {
            ++Iter1;
          }
          ++Iter2;
        } else {
          ++Iter1;
        }
      }
      CurrElementIter = Elements.begin();
      return changed;
    }
  
    bool intersectWithComplement(const SparseBitVector<ElementSize> *RHS) const {
      return intersectWithComplement(*RHS);
    }
  
    //  Three argument version of intersectWithComplement.
    //  Result of RHS1 & ~RHS2 is stored into this bitmap.
    void intersectWithComplement(const SparseBitVector<ElementSize> &RHS1,
                                 const SparseBitVector<ElementSize> &RHS2)
    {
      if (this == &RHS1) {
        intersectWithComplement(RHS2);
        return;
      } else if (this == &RHS2) {
        SparseBitVector RHS2Copy(RHS2);
        intersectWithComplement(RHS1, RHS2Copy);
        return;
      }
  
      Elements.clear();
      CurrElementIter = Elements.begin();
      ElementListConstIter Iter1 = RHS1.Elements.begin();
      ElementListConstIter Iter2 = RHS2.Elements.begin();
  
      // If RHS1 is empty, we are done
      // If RHS2 is empty, we still have to copy RHS1
      if (RHS1.Elements.empty())
        return;
  
      // Loop through, intersecting as we go, erasing elements when necessary.
      while (Iter2 != RHS2.Elements.end()) {
        if (Iter1 == RHS1.Elements.end())
          return;
  
        if (Iter1->index() > Iter2->index()) {
          ++Iter2;
        } else if (Iter1->index() == Iter2->index()) {
          bool BecameZero = false;
          Elements.emplace_back(Iter1->index());
          Elements.back().intersectWithComplement(*Iter1, *Iter2, BecameZero);
          if (BecameZero)
            Elements.pop_back();
          ++Iter1;
          ++Iter2;
        } else {
          Elements.push_back(*Iter1++);
        }
      }
  
      // copy the remaining elements
      std::copy(Iter1, RHS1.Elements.end(), std::back_inserter(Elements));
    }
  
    void intersectWithComplement(const SparseBitVector<ElementSize> *RHS1,
                                 const SparseBitVector<ElementSize> *RHS2) {
      intersectWithComplement(*RHS1, *RHS2);
    }
  
    bool intersects(const SparseBitVector<ElementSize> *RHS) const {
      return intersects(*RHS);
    }
  
    // Return true if we share any bits in common with RHS
    bool intersects(const SparseBitVector<ElementSize> &RHS) const {
      ElementListConstIter Iter1 = Elements.begin();
      ElementListConstIter Iter2 = RHS.Elements.begin();
  
      // Check if both bitmaps are empty.
      if (Elements.empty() && RHS.Elements.empty())
        return false;
  
      // Loop through, intersecting stopping when we hit bits in common.
      while (Iter2 != RHS.Elements.end()) {
        if (Iter1 == Elements.end())
          return false;
  
        if (Iter1->index() > Iter2->index()) {
          ++Iter2;
        } else if (Iter1->index() == Iter2->index()) {
          if (Iter1->intersects(*Iter2))
            return true;
          ++Iter1;
          ++Iter2;
        } else {
          ++Iter1;
        }
      }
      return false;
    }
  
    // Return true iff all bits set in this SparseBitVector are
    // also set in RHS.
    bool contains(const SparseBitVector<ElementSize> &RHS) const {
      SparseBitVector<ElementSize> Result(*this);
      Result &= RHS;
      return (Result == RHS);
    }
  
    // Return the first set bit in the bitmap.  Return -1 if no bits are set.
    int find_first() const {
      if (Elements.empty())
        return -1;
      const SparseBitVectorElement<ElementSize> &First = *(Elements.begin());
      return (First.index() * ElementSize) + First.find_first();
    }
  
    // Return the last set bit in the bitmap.  Return -1 if no bits are set.
    int find_last() const {
      if (Elements.empty())
        return -1;
      const SparseBitVectorElement<ElementSize> &Last = *(Elements.rbegin());
      return (Last.index() * ElementSize) + Last.find_last();
    }
  
    // Return true if the SparseBitVector is empty
    bool empty() const {
      return Elements.empty();
    }
  
    unsigned count() const {
      unsigned BitCount = 0;
      for (ElementListConstIter Iter = Elements.begin();
           Iter != Elements.end();
           ++Iter)
        BitCount += Iter->count();
  
      return BitCount;
    }
  
    iterator begin() const {
      return iterator(this);
    }
  
    iterator end() const {
      return iterator(this, true);
    }
  };
  
  // Convenience functions to allow Or and And without dereferencing in the user
  // code.
  
  template <unsigned ElementSize>
  inline bool operator |=(SparseBitVector<ElementSize> &LHS,
                          const SparseBitVector<ElementSize> *RHS) {
    return LHS |= *RHS;
  }
  
  template <unsigned ElementSize>
  inline bool operator |=(SparseBitVector<ElementSize> *LHS,
                          const SparseBitVector<ElementSize> &RHS) {
    return LHS->operator|=(RHS);
  }
  
  template <unsigned ElementSize>
  inline bool operator &=(SparseBitVector<ElementSize> *LHS,
                          const SparseBitVector<ElementSize> &RHS) {
    return LHS->operator&=(RHS);
  }
  
  template <unsigned ElementSize>
  inline bool operator &=(SparseBitVector<ElementSize> &LHS,
                          const SparseBitVector<ElementSize> *RHS) {
    return LHS &= *RHS;
  }
  
  // Convenience functions for infix union, intersection, difference operators.
  
  template <unsigned ElementSize>
  inline SparseBitVector<ElementSize>
  operator|(const SparseBitVector<ElementSize> &LHS,
            const SparseBitVector<ElementSize> &RHS) {
    SparseBitVector<ElementSize> Result(LHS);
    Result |= RHS;
    return Result;
  }
  
  template <unsigned ElementSize>
  inline SparseBitVector<ElementSize>
  operator&(const SparseBitVector<ElementSize> &LHS,
            const SparseBitVector<ElementSize> &RHS) {
    SparseBitVector<ElementSize> Result(LHS);
    Result &= RHS;
    return Result;
  }
  
  template <unsigned ElementSize>
  inline SparseBitVector<ElementSize>
  operator-(const SparseBitVector<ElementSize> &LHS,
            const SparseBitVector<ElementSize> &RHS) {
    SparseBitVector<ElementSize> Result;
    Result.intersectWithComplement(LHS, RHS);
    return Result;
  }
  
  // Dump a SparseBitVector to a stream
  template <unsigned ElementSize>
  void dump(const SparseBitVector<ElementSize> &LHS, raw_ostream &out) {
    out << "[";
  
    typename SparseBitVector<ElementSize>::iterator bi = LHS.begin(),
      be = LHS.end();
    if (bi != be) {
      out << *bi;
      for (++bi; bi != be; ++bi) {
        out << " " << *bi;
      }
    }
    out << "]\n";
  }
  
  } // end namespace llvm
  
  #endif // LLVM_ADT_SPARSEBITVECTOR_H
  