llvm/ADT/DenseMap.h

//===- llvm/ADT/DenseMap.h - Dense probed hash table ------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Chris Lattner and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the DenseMap class.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_DENSEMAP_H
#define LLVM_ADT_DENSEMAP_H

#include "llvm/Support/DataTypes.h"
#include <cassert>

namespace llvm {

template<typename T>
struct DenseMapKeyInfo {
  //static inline T getEmptyKey();
  //static inline T getTombstoneKey();
  //static unsigned getHashValue(const T &Val);
  //static bool isPod()
};

template<typename T>
struct DenseMapKeyInfo<T*> {
  static inline T* getEmptyKey() { return (T*)-1; }
  static inline T* getTombstoneKey() { return (T*)-2; }
  static unsigned getHashValue(const T *PtrVal) {
    return (unsigned)((uintptr_t)PtrVal >> 4) ^
           (unsigned)((uintptr_t)PtrVal >> 9);
  }
  static bool isPod() { return true; }
};


template<typename KeyT, typename ValueT>
class DenseMap {
  struct BucketT { KeyT Key; ValueT Value; };
  unsigned NumBuckets;
  BucketT *Buckets;

  unsigned NumEntries;
  DenseMap(const DenseMap &); // not implemented.
public:
  explicit DenseMap(unsigned NumInitBuckets = 8) {
    init(NumInitBuckets);
  }
  ~DenseMap() {
    const KeyT EmptyKey = getEmptyKey(), TombstoneKey = getTombstoneKey();
    for (BucketT *P = Buckets, *E = Buckets+NumBuckets; P != E; ++P) {
      if (P->Key != EmptyKey && P->Key != TombstoneKey)
        P->Value.~ValueT();
      P->Key.~KeyT();
    }
    delete[] (char*)Buckets;
  }

  unsigned size() const { return NumEntries; }

  void clear() {
    const KeyT EmptyKey = getEmptyKey(), TombstoneKey = getTombstoneKey();
    for (BucketT *P = Buckets, *E = Buckets+NumBuckets; P != E; ++P) {
      if (P->Key != EmptyKey && P->Key != TombstoneKey) {
        P->Key = EmptyKey;
        P->Value.~ValueT();
        --NumEntries;
      }
    }
    assert(NumEntries == 0 && "Node count imbalance!");
  }

  /// count - Return true if the specified key is in the map.
  bool count(const KeyT &Val) const {
    BucketT *TheBucket;
    return LookupBucketFor(Val, TheBucket);
  }

  ValueT &operator[](const KeyT &Val) {
    BucketT *TheBucket;
    if (LookupBucketFor(Val, TheBucket))
      return TheBucket->Value;

    // If the load of the hash table is more than 3/4, grow it.
    if (NumEntries*4 >= NumBuckets*3) {
      this->grow();
      LookupBucketFor(Val, TheBucket);
    }
    ++NumEntries;
    TheBucket->Key = Val;
    new (&TheBucket->Value) ValueT();
    return TheBucket->Value;
  }

private:
  unsigned getHashValue(const KeyT &Val) const {
    return DenseMapKeyInfo<KeyT>::getHashValue(Val);
  }
  const KeyT getEmptyKey() const { return DenseMapKeyInfo<KeyT>::getEmptyKey();}
  const KeyT getTombstoneKey() const {
    return DenseMapKeyInfo<KeyT>::getTombstoneKey();
  }

  /// LookupBucketFor - Lookup the appropriate bucket for Val, returning it in
  /// FoundBucket.  If the bucket contains the key and a value, this returns
  /// true, otherwise it returns a bucket with an empty marker or tombstone and
  /// returns false.
  bool LookupBucketFor(const KeyT &Val, BucketT *&FoundBucket) const {
    unsigned BucketNo = getHashValue(Val);
    unsigned ProbeAmt = 1;
    BucketT *BucketsPtr = Buckets;

    // FoundTombstone - Keep track of whether we find a tombstone while probing.
    BucketT *FoundTombstone = 0;
    const KeyT EmptyKey = getEmptyKey();
    const KeyT TombstoneKey = getTombstoneKey();
    assert(Val != EmptyKey && Val != TombstoneKey &&
           "Empty/Tombstone value shouldn't be inserted into map!");

    while (1) {
      BucketT *ThisBucket = BucketsPtr + (BucketNo & (NumBuckets-1));
      // Found Val's bucket?  If so, return it.
      if (ThisBucket->Key == Val) {
        FoundBucket = ThisBucket;
        return true;
      }

      // If we found an empty bucket, the key doesn't exist in the set.
      // Insert it and return the default value.
      if (ThisBucket->Key == EmptyKey) {
        // If we've already seen a tombstone while probing, fill it in instead
        // of the empty bucket we eventually probed to.
        if (FoundTombstone) ThisBucket = FoundTombstone;
        FoundBucket = FoundTombstone ? FoundTombstone : ThisBucket;
        return false;
      }

      // If this is a tombstone, remember it.  If Val ends up not in the map, we
      // prefer to return it than something that would require more probing.
      if (ThisBucket->Key == TombstoneKey && !FoundTombstone)
        FoundTombstone = ThisBucket;  // Remember the first tombstone found.

      // Otherwise, it's a hash collision or a tombstone, continue quadratic
      // probing.
      BucketNo += ProbeAmt++;
    }
  }

  void init(unsigned InitBuckets) {
    NumEntries = 0;
    NumBuckets = InitBuckets;
    assert(InitBuckets && (InitBuckets & InitBuckets-1) == 0 &&
           "# initial buckets must be a power of two!");
    Buckets = (BucketT*)new char[sizeof(BucketT)*InitBuckets];
    // Initialize all the keys to EmptyKey.
    const KeyT EmptyKey = getEmptyKey();
    for (unsigned i = 0; i != InitBuckets; ++i)
      new (&Buckets[i].Key) KeyT(EmptyKey);
  }

  void grow() {
    unsigned OldNumBuckets = NumBuckets;
    BucketT *OldBuckets = Buckets;

    // Double the number of buckets.
    NumBuckets <<= 1;
    Buckets = (BucketT*)new char[sizeof(BucketT)*NumBuckets];

    // Initialize all the keys to EmptyKey.
    const KeyT EmptyKey = getEmptyKey();
    for (unsigned i = 0, e = NumBuckets; i != e; ++i)
      new (&Buckets[i].Key) KeyT(EmptyKey);

    // Insert all the old elements.
    const KeyT TombstoneKey = getTombstoneKey();
    for (BucketT *B = OldBuckets, *E = OldBuckets+OldNumBuckets; B != E; ++B) {
      if (B->Key != EmptyKey && B->Key != TombstoneKey) {
        // Insert the key/value into the new table.
        BucketT *DestBucket;
        bool FoundVal = LookupBucketFor(B->Key, DestBucket);
        assert(!FoundVal && "Key already in new map?");
        DestBucket->Key = B->Key;
        new (&DestBucket->Value) ValueT(B->Value);

        // Free the value.
        B->Value.~ValueT();
      }
      B->Key.~KeyT();
    }

    // Free the old table.
    delete[] (char*)OldBuckets;
  }
};

} // end namespace llvm

#endif