SmallPtrSet.h

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//===- 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
// SmallPtrSetImpl for more details on the algorithm used.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_SMALLPTRSET_H
#define LLVM_ADT_SMALLPTRSET_H

#include <cassert>
#include <cstddef>
#include <cstring>
#include <iterator>
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/PointerLikeTypeTraits.h"

namespace llvm {

class SmallPtrSetIteratorImpl;

class SmallPtrSetImpl {
  friend class SmallPtrSetIteratorImpl;
protected:
  const void **SmallArray;
  const void **CurArray;
  unsigned CurArraySize;

  // If small, this is # elts allocated consecutively
  unsigned NumElements;
  unsigned NumTombstones;

  // Helper to copy construct a SmallPtrSet.
  SmallPtrSetImpl(const void **SmallStorage, const SmallPtrSetImpl& that);
  explicit SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize) :
    SmallArray(SmallStorage), CurArray(SmallStorage), CurArraySize(SmallSize) {
    assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
           "Initial size must be a power of two!");
    // The end pointer, always valid, is set to a valid element to help the
    // iterator.
    CurArray[SmallSize] = 0;
    clear();
  }
  ~SmallPtrSetImpl();

public:
  bool empty() const { return size() == 0; }
  unsigned size() const { return NumElements; }

  void clear() {
    // If the capacity of the array is huge, and the # elements used is small,
    // shrink the array.
    if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32)
      return shrink_and_clear();

    // Fill the array with empty markers.
    memset(CurArray, -1, CurArraySize*sizeof(void*));
    NumElements = 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);
  }

  bool insert_imp(const void * Ptr);

  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+NumElements; APtr != E; ++APtr)
        if (*APtr == Ptr)
          return true;
      return false;
    }

    // Big set case.
    return *FindBucketFor(Ptr) == Ptr;
  }

private:
  bool isSmall() const { return CurArray == SmallArray; }

  unsigned Hash(const void *Ptr) const {
    return static_cast<unsigned>(((uintptr_t)Ptr >> 4) & (CurArraySize-1));
  }
  const void * const *FindBucketFor(const void *Ptr) const;
  void shrink_and_clear();

  void Grow(unsigned NewSize);

  void operator=(const SmallPtrSetImpl &RHS);  // DO NOT IMPLEMENT.
protected:
  void CopyFrom(const SmallPtrSetImpl &RHS);
};

class SmallPtrSetIteratorImpl {
protected:
  const void *const *Bucket;
public:
  explicit SmallPtrSetIteratorImpl(const void *const *BP) : Bucket(BP) {
    AdvanceIfNotValid();
  }

  bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
    return Bucket == RHS.Bucket;
  }
  bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
    return Bucket != RHS.Bucket;
  }

protected:
  void AdvanceIfNotValid() {
    while (*Bucket == SmallPtrSetImpl::getEmptyMarker() ||
           *Bucket == SmallPtrSetImpl::getTombstoneMarker())
      ++Bucket;
  }
};

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)
    : SmallPtrSetIteratorImpl(BP) {}

  // Most methods provided by baseclass.

  const PtrTy operator*() const {
    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;
  }
};

template<unsigned N>
struct 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 };
};
  

template<class PtrType, unsigned SmallSize>
class SmallPtrSet : public SmallPtrSetImpl {
  // Make sure that SmallSize is a power of two, round up if not.
  enum { SmallSizePowTwo = RoundUpToPowerOfTwo<SmallSize>::Val };
  const void *SmallStorage[SmallSizePowTwo+1];
  typedef PointerLikeTypeTraits<PtrType> PtrTraits;
public:
  SmallPtrSet() : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {}
  SmallPtrSet(const SmallPtrSet &that) : SmallPtrSetImpl(SmallStorage, that) {}

  template<typename It>
  SmallPtrSet(It I, It E) : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {
    insert(I, E);
  }

  bool insert(PtrType Ptr) {
    return insert_imp(PtrTraits::getAsVoidPointer(Ptr));
  }

  bool erase(PtrType Ptr) {
    return erase_imp(PtrTraits::getAsVoidPointer(Ptr));
  }

  bool count(PtrType Ptr) const {
    return count_imp(PtrTraits::getAsVoidPointer(Ptr));
  }

  template <typename IterT>
  void insert(IterT I, IterT E) {
    for (; I != E; ++I)
      insert(*I);
  }

  typedef SmallPtrSetIterator<PtrType> iterator;
  typedef SmallPtrSetIterator<PtrType> const_iterator;
  inline iterator begin() const {
    return iterator(CurArray);
  }
  inline iterator end() const {
    return iterator(CurArray+CurArraySize);
  }

  // Allow assignment from any smallptrset with the same element type even if it
  // doesn't have the same smallsize.
  const SmallPtrSet<PtrType, SmallSize>&
  operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) {
    CopyFrom(RHS);
    return *this;
  }

};

}

#endif

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