llvm/ADT/StringMap.h

//===--- StringMap.h - String Hash table map interface ----------*- 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 StringMap class.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_STRINGMAP_H
#define LLVM_ADT_STRINGMAP_H

#include "llvm/Support/Allocator.h"
#include <cstring>

namespace llvm {

/// StringMapEntryBase - Shared base class of StringMapEntry instances.
class StringMapEntryBase {
  unsigned StrLen;
public:
  StringMapEntryBase(unsigned Len) : StrLen(Len) {}

  unsigned getKeyLength() const { return StrLen; }
};

/// StringMapVisitor - Subclasses of this class may be implemented to walk all
/// of the items in a StringMap.
class StringMapVisitor {
public:
  virtual ~StringMapVisitor();
  virtual void Visit(const char *Key, StringMapEntryBase *Value) const = 0;
};

/// StringMapImpl - This is the base class of StringMap that is shared among
/// all of its instantiations.
class StringMapImpl {
protected:
  /// ItemBucket - The hash table consists of an array of these.  If Item is
  /// non-null, this is an extant entry, otherwise, it is a hole.
  struct ItemBucket {
    /// FullHashValue - This remembers the full hash value of the key for
    /// easy scanning.
    unsigned FullHashValue;

    /// Item - This is a pointer to the actual item object.
    StringMapEntryBase *Item;
  };

  ItemBucket *TheTable;
  unsigned NumBuckets;
  unsigned NumItems;
  unsigned ItemSize;
protected:
  StringMapImpl(unsigned InitSize, unsigned ItemSize);
  void RehashTable();

  /// LookupBucketFor - Look up the bucket that the specified string should end
  /// up in.  If it already exists as a key in the map, the Item pointer for the
  /// specified bucket will be non-null.  Otherwise, it will be null.  In either
  /// case, the FullHashValue field of the bucket will be set to the hash value
  /// of the string.
  unsigned LookupBucketFor(const char *KeyStart, const char *KeyEnd);

public:
  unsigned getNumBuckets() const { return NumBuckets; }
  unsigned getNumItems() const { return NumItems; }

  void VisitEntries(const StringMapVisitor &Visitor) const;
};

/// StringMapEntry - This is used to represent one value that is inserted into
/// a StringMap.  It contains the Value itself and the key: the string length
/// and data.
template<typename ValueTy>
class StringMapEntry : public StringMapEntryBase {
  ValueTy Val;
public:
  StringMapEntry(unsigned StrLen)
    : StringMapEntryBase(StrLen), Val() {}
  StringMapEntry(unsigned StrLen, const ValueTy &V)
    : StringMapEntryBase(StrLen), Val(V) {}

  const ValueTy &getValue() const { return Val; }
  ValueTy &getValue() { return Val; }

  void setValue(const ValueTy &V) { Val = V; }

  /// getKeyData - Return the start of the string data that is the key for this
  /// value.  The string data is always stored immediately after the
  /// StringMapEntry object.
  const char *getKeyData() const {return reinterpret_cast<const char*>(this+1);}
};


/// StringMap - This is an unconventional map that is specialized for handling
/// keys that are "strings", which are basically ranges of bytes. This does some
/// funky memory allocation and hashing things to make it extremely efficient,
/// storing the string data *after* the value in the map.
template<typename ValueTy, typename AllocatorTy = MallocAllocator>
class StringMap : public StringMapImpl {
  AllocatorTy Allocator;
  typedef StringMapEntry<ValueTy> MapEntryTy;
public:
  StringMap(unsigned InitialSize = 0)
    : StringMapImpl(InitialSize, sizeof(MapEntryTy)) {}

  AllocatorTy &getAllocator() { return Allocator; }
  const AllocatorTy &getAllocator() const { return Allocator; }

  /// FindValue - Look up the specified key in the map.  If it exists, return a
  /// pointer to the element, otherwise return null.
  MapEntryTy *FindValue(const char *KeyStart, const char *KeyEnd) {
    unsigned BucketNo = LookupBucketFor(KeyStart, KeyEnd);
    return static_cast<MapEntryTy*>(TheTable[BucketNo].Item);
  }

  /// GetOrCreateValue - Look up the specified key in the table.  If a value
  /// exists, return it.  Otherwise, default construct a value, insert it, and
  /// return.
  StringMapEntry<ValueTy> &GetOrCreateValue(const char *KeyStart,
                                            const char *KeyEnd) {
    unsigned BucketNo = LookupBucketFor(KeyStart, KeyEnd);
    ItemBucket &Bucket = TheTable[BucketNo];
    if (Bucket.Item)
      return *static_cast<MapEntryTy*>(Bucket.Item);

    unsigned KeyLength = KeyEnd-KeyStart;

    // Okay, the item doesn't already exist, and 'Bucket' is the bucket to fill
    // in.  Allocate a new item with space for the string at the end and a null
    // terminator.
    unsigned AllocSize = sizeof(MapEntryTy)+KeyLength+1;

#ifdef __GNUC__
    unsigned Alignment = __alignof__(MapEntryTy);
#else
    // FIXME: ugly.
    unsigned Alignment = 8;
#endif
    MapEntryTy *NewItem =
      static_cast<MapEntryTy*>(Allocator.Allocate(AllocSize, Alignment));

    // Default construct the value.
    new (NewItem) MapEntryTy(KeyLength);
    ++NumItems;

    // Copy the string information.
    char *StrBuffer = const_cast<char*>(NewItem->getKeyData());
    memcpy(StrBuffer, KeyStart, KeyLength);
    StrBuffer[KeyLength] = 0;  // Null terminate for convenience of clients.

    // Fill in the bucket for the hash table.  The FullHashValue was already
    // filled in by LookupBucketFor.
    Bucket.Item = NewItem;

    // If the hash table is now more than 3/4 full, rehash into a larger table.
    if (NumItems > NumBuckets*3/4)
      RehashTable();
    return *NewItem;
  }

  ~StringMap() {
    for (ItemBucket *I = TheTable, *E = TheTable+NumBuckets; I != E; ++I) {
      if (MapEntryTy *Id = static_cast<MapEntryTy*>(I->Item)) {
        // Free memory referenced by the item.
        Id->~MapEntryTy();
        Allocator.Deallocate(Id);
      }
    }
    delete [] TheTable;
  }
};

}

#endif