THashTable.cxx

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// @(#)root/cont:$Id$
// Author: Fons Rademakers   27/09/95

/*************************************************************************
 * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

/** \class THashTable
THashTable implements a hash table to store TObject's. The hash
value is calculated using the value returned by the TObject's
Hash() function. Each class inheriting from TObject can override
Hash() as it sees fit.

THashTable does not preserve the insertion order of the objects.
If the insertion order is important AND fast retrieval is needed
use THashList instead.
*/

#include "THashTable.h"
#include "TObjectTable.h"
#include "TList.h"
#include "TError.h"

ClassImp(THashTable)

////////////////////////////////////////////////////////////////////////////////
/// Create a THashTable object. Capacity is the initial hashtable capacity
/// (i.e. number of slots), by default kInitHashTableCapacity = 17, and
/// rehashlevel is the value at which a rehash will be triggered. I.e. when
/// the average size of the linked lists at a slot becomes longer than
/// rehashlevel then the hashtable will be resized and refilled to reduce
/// the collision rate to about 1. The higher the collision rate, i.e. the
/// longer the linked lists, the longer lookup will take. If rehashlevel=0
/// the table will NOT automatically be rehashed. Use Rehash() for manual
/// rehashing.

THashTable::THashTable(Int_t capacity, Int_t rehashlevel)
{
   if (capacity < 0) {
      Warning("THashTable", "capacity (%d) < 0", capacity);
      capacity = TCollection::kInitHashTableCapacity;
   } else if (capacity == 0)
      capacity = TCollection::kInitHashTableCapacity;

   fSize = (Int_t)TMath::NextPrime(TMath::Max(capacity,(int)TCollection::kInitHashTableCapacity));
   fCont = new TList* [fSize];
   memset(fCont, 0, fSize*sizeof(TList*));

   fEntries   = 0;
   fUsedSlots = 0;
   if (rehashlevel < 2) rehashlevel = 0;
   fRehashLevel = rehashlevel;
}

////////////////////////////////////////////////////////////////////////////////
/// Delete a hashtable. Objects are not deleted unless the THashTable is the
/// owner (set via SetOwner()).

THashTable::~THashTable()
{
   if (fCont) Clear();
   delete [] fCont;
   fCont = 0;
   fSize = 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Add object to the hash table. Its position in the table will be
/// determined by the value returned by its Hash() function.

void THashTable::Add(TObject *obj)
{
   if (IsArgNull("Add", obj)) return;

   Int_t slot = GetHashValue(obj);
   if (!fCont[slot]) {
      fCont[slot] = new TList;
      fUsedSlots++;
   }
   fCont[slot]->Add(obj);
   fEntries++;

   if (fRehashLevel && AverageCollisions() > fRehashLevel)
      Rehash(fEntries);
}

////////////////////////////////////////////////////////////////////////////////
/// Add object to the hash table. Its position in the table will be
/// determined by the value returned by its Hash() function.
/// If and only if 'before' is in the same bucket as obj, obj is added
/// in front of 'before' within the bucket's list.

void THashTable::AddBefore(const TObject *before, TObject *obj)
{
   if (IsArgNull("Add", obj)) return;

   Int_t slot = GetHashValue(obj);
   if (!fCont[slot]) {
      fCont[slot] = new TList;
      fUsedSlots++;
   }
   if (before && GetHashValue(before) == slot) {
      fCont[slot]->AddBefore(before,obj);
   } else {
      fCont[slot]->Add(obj);
   }
   fEntries++;

   if (fRehashLevel && AverageCollisions() > fRehashLevel)
      Rehash(fEntries);
}

////////////////////////////////////////////////////////////////////////////////
/// Add all objects from collection col to this collection.
/// Implemented for more efficient rehashing.

void THashTable::AddAll(const TCollection *col)
{
   // Hashing after AddAll can be much more expensive than
   // hashing before, as we need to add more elements.
   // We assume an ideal hash, i.e. fUsedSlots==fSize.
   Int_t sumEntries=fEntries+col->GetEntries();
   Bool_t rehashBefore=fRehashLevel && (sumEntries > fSize*fRehashLevel);
   if (rehashBefore)
      Rehash(sumEntries);

   // prevent Add from Rehashing
   Int_t saveRehashLevel=fRehashLevel;
   fRehashLevel=0;

   TCollection::AddAll(col);

   fRehashLevel=saveRehashLevel;
   // If we didn't Rehash before, we might have to do it
   // now, due to a non-perfect hash function.
   if (!rehashBefore && fRehashLevel && AverageCollisions() > fRehashLevel)
      Rehash(fEntries);
}

////////////////////////////////////////////////////////////////////////////////
/// Remove all objects from the table. Does not delete the objects
/// unless the THashTable is the owner (set via SetOwner()).

void THashTable::Clear(Option_t *option)
{
   for (int i = 0; i < fSize; i++) {
      // option "nodelete" is passed when Clear is called from
      // THashList::Clear() or THashList::Delete() or Rehash().
      if (fCont[i]) {
         if (IsOwner())
            fCont[i]->SetOwner();
         fCont[i]->Clear(option);
      }
      SafeDelete(fCont[i]);
   }

   fEntries   = 0;
   fUsedSlots = 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Returns the number of collisions for an object with a certain name
/// (i.e. number of objects in same slot in the hash table, i.e. length
/// of linked list).

Int_t THashTable::Collisions(const char *name) const
{
   Int_t slot = GetHashValue(name);
   if (fCont[slot]) return fCont[slot]->GetSize();
   return 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Returns the number of collisions for an object (i.e. number of objects
/// in same slot in the hash table, i.e. length of linked list).

Int_t THashTable::Collisions(TObject *obj) const
{
   if (IsArgNull("Collisions", obj)) return 0;

   Int_t slot = GetHashValue(obj);
   if (fCont[slot]) return fCont[slot]->GetSize();
   return 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Remove all objects from the table AND delete all heap based objects.

void THashTable::Delete(Option_t *)
{
   for (int i = 0; i < fSize; i++)
      if (fCont[i]) {
         fCont[i]->Delete();
         SafeDelete(fCont[i]);
      }

   fEntries   = 0;
   fUsedSlots = 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Find object using its name. Uses the hash value returned by the
/// TString::Hash() after converting name to a TString.

TObject *THashTable::FindObject(const char *name) const
{
   Int_t slot = GetHashValue(name);
   if (fCont[slot]) return fCont[slot]->FindObject(name);
   return 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Find object using its hash value (returned by its Hash() member).

TObject *THashTable::FindObject(const TObject *obj) const
{
   if (IsArgNull("FindObject", obj)) return 0;

   Int_t slot = GetHashValue(obj);
   if (fCont[slot]) return fCont[slot]->FindObject(obj);
   return 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Return the TList corresponding to object's name based hash value.
/// One can iterate this list "manually" to find, e.g. objects with
/// the same name.

const TList *THashTable::GetListForObject(const char *name) const
{
   return fCont[GetHashValue(name)];
}

////////////////////////////////////////////////////////////////////////////////
/// Return the TList corresponding to object's hash value.
/// One can iterate this list "manually" to find, e.g. identical
/// objects.

const TList *THashTable::GetListForObject(const TObject *obj) const
{
   if (IsArgNull("GetListForObject", obj)) return 0;
   return fCont[GetHashValue(obj)];
}

////////////////////////////////////////////////////////////////////////////////
/// Return address of pointer to obj

TObject **THashTable::GetObjectRef(const TObject *obj) const
{
   if (IsArgNull("GetObjectRef", obj)) return 0;

   Int_t slot = GetHashValue(obj);
   if (fCont[slot]) return fCont[slot]->GetObjectRef(obj);
   return 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Returns a hash table iterator.

TIterator *THashTable::MakeIterator(Bool_t dir) const
{
   return new THashTableIter(this, dir);
}

////////////////////////////////////////////////////////////////////////////////
/// Rehash the hashtable. If the collision rate becomes too high (i.e.
/// the average size of the linked lists become too long) then lookup
/// efficiency decreases since relatively long lists have to be searched
/// every time. To improve performance rehash the hashtable. This resizes
/// the table to newCapacity slots and refills the table. Use
/// AverageCollisions() to check if you need to rehash. Set checkObjValidity
/// to kFALSE if you know that all objects in the table are still valid
/// (i.e. have not been deleted from the system in the meanwhile).

void THashTable::Rehash(Int_t newCapacity, Bool_t checkObjValidity)
{
   THashTable *ht = new THashTable(newCapacity);

   TIter next(this);
   TObject *obj;

   if (checkObjValidity && TObject::GetObjectStat() && gObjectTable) {
      while ((obj = next()))
         if (gObjectTable->PtrIsValid(obj)) ht->Add(obj);
   } else {
      while ((obj = next()))
         ht->Add(obj);
   }

   Clear("nodelete");
   delete [] fCont;
   fCont = ht->fCont;
   ht->fCont = 0;

   fSize      = ht->fSize;     // idem
   fEntries   = ht->fEntries;
   fUsedSlots = ht->fUsedSlots;

   // this should not happen, but it will prevent an endless loop
   // in case of a very bad hash function
   if (fRehashLevel && AverageCollisions() > fRehashLevel)
      fRehashLevel = (int)AverageCollisions() + 1;

   delete ht;
}

////////////////////////////////////////////////////////////////////////////////
/// Remove object from the hashtable.

TObject *THashTable::Remove(TObject *obj)
{
   Int_t slot = GetHashValue(obj);
   if (fCont[slot]) {
      TObject *ob = fCont[slot]->Remove(obj);
      if (ob) {
         fEntries--;
         if (fCont[slot]->GetSize() == 0) {
            SafeDelete(fCont[slot]);
            fUsedSlots--;
         }
         return ob;
      }
   }
   return 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Remove object from the hashtable without using the hash value.

TObject *THashTable::RemoveSlow(TObject *obj)
{
   for (int i = 0; i < fSize; i++) {
      if (fCont[i]) {
         TObject *ob = fCont[i]->Remove(obj);
         if (ob) {
            fEntries--;
            if (fCont[i]->GetSize() == 0) {
               SafeDelete(fCont[i]);
               fUsedSlots--;
            }
            return ob;
         }
      }
   }
   return 0;
}

/** \class THashTableIter
Iterator of hash table.
*/

ClassImp(THashTableIter)

////////////////////////////////////////////////////////////////////////////////
/// Create a hashtable iterator. By default the iteration direction
/// is kIterForward. To go backward use kIterBackward.

THashTableIter::THashTableIter(const THashTable *ht, Bool_t dir)
{
   fTable      = ht;
   fDirection  = dir;
   fListCursor = 0;
   Reset();
}

////////////////////////////////////////////////////////////////////////////////
/// Copy ctor.

THashTableIter::THashTableIter(const THashTableIter &iter) : TIterator(iter)
{
   fTable      = iter.fTable;
   fDirection  = iter.fDirection;
   fCursor     = iter.fCursor;
   fListCursor = 0;
   if (iter.fListCursor) {
      fListCursor = (TListIter *)iter.fListCursor->GetCollection()->MakeIterator();
      if (fListCursor)
         fListCursor->operator=(*iter.fListCursor);
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Overridden assignment operator.

TIterator &THashTableIter::operator=(const TIterator &rhs)
{
   if (this != &rhs && rhs.IsA() == THashTableIter::Class()) {
      const THashTableIter &rhs1 = (const THashTableIter &)rhs;
      fTable     = rhs1.fTable;
      fDirection = rhs1.fDirection;
      fCursor    = rhs1.fCursor;
      if (rhs1.fListCursor) {
         fListCursor = (TListIter *)rhs1.fListCursor->GetCollection()->MakeIterator();
         if (fListCursor)
            fListCursor->operator=(*rhs1.fListCursor);
      }
   }
   return *this;
}

////////////////////////////////////////////////////////////////////////////////
/// Overloaded assignment operator.

THashTableIter &THashTableIter::operator=(const THashTableIter &rhs)
{
   if (this != &rhs) {
      fTable     = rhs.fTable;
      fDirection = rhs.fDirection;
      fCursor    = rhs.fCursor;
      if (rhs.fListCursor) {
         fListCursor = (TListIter *)rhs.fListCursor->GetCollection()->MakeIterator();
         if (fListCursor)
            fListCursor->operator=(*rhs.fListCursor);
      }
   }
   return *this;
}

////////////////////////////////////////////////////////////////////////////////
/// Delete hashtable iterator.

THashTableIter::~THashTableIter()
{
   delete fListCursor;
}

////////////////////////////////////////////////////////////////////////////////
/// Return next object in hashtable. Returns 0 when no more objects in table.

TObject *THashTableIter::Next()
{
   while (kTRUE) {
      if (!fListCursor) {
         int slot = NextSlot();
         if (slot == -1) return 0;
         fListCursor = new TListIter(fTable->fCont[slot], fDirection);
      }

      TObject *obj = fListCursor->Next();
      if (obj) return obj;

      SafeDelete(fListCursor);
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Returns index of next slot in table containing list to be iterated.

Int_t THashTableIter::NextSlot()
{
   if (fDirection == kIterForward) {
      for ( ; fCursor < fTable->Capacity() && fTable->fCont[fCursor] == 0;
              fCursor++) { }

      if (fCursor < fTable->Capacity())
         return fCursor++;

   } else {
      for ( ; fCursor >= 0 && fTable->fCont[fCursor] == 0;
              fCursor--) { }

      if (fCursor >= 0)
         return fCursor--;
   }
   return -1;
}

////////////////////////////////////////////////////////////////////////////////
/// Reset the hashtable iterator. Either to beginning or end, depending on
/// the initial iteration direction.

void THashTableIter::Reset()
{
   if (fDirection == kIterForward)
      fCursor = 0;
   else
      fCursor = fTable->Capacity() - 1;
   SafeDelete(fListCursor);
}

////////////////////////////////////////////////////////////////////////////////
/// This operator compares two TIterator objects.

Bool_t THashTableIter::operator!=(const TIterator &aIter) const
{
   if (aIter.IsA() == THashTableIter::Class()) {
      const THashTableIter &iter(dynamic_cast<const THashTableIter &>(aIter));
      return (fListCursor != iter.fListCursor);
   }
   return false; // for base class we don't implement a comparison
}

////////////////////////////////////////////////////////////////////////////////
/// This operator compares two THashTableIter objects.

Bool_t THashTableIter::operator!=(const THashTableIter &aIter) const
{
   return (fListCursor != aIter.fListCursor);
}

////////////////////////////////////////////////////////////////////////////////
/// Return pointer to current object or nullptr.

TObject *THashTableIter::operator*() const
{
   return (fListCursor ? fListCursor->operator*() : nullptr);
}