gecko/xpcom/ds/nsCheapSets.h

173 lines
4.3 KiB
C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla Communicator client code.
*
* The Initial Developer of the Original Code is
* Netscape Communications Corporation.
* Portions created by the Initial Developer are Copyright (C) 1998
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
*
* Alternatively, the contents of this file may be used under the terms of
* either of the GNU General Public License Version 2 or later (the "GPL"),
* or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#ifndef __nsCheapSets_h__
#define __nsCheapSets_h__
#include "nsTHashtable.h"
#include "mozilla/StandardInteger.h"
/**
* A set that takes up minimal size when there are 0 or 1 entries in the set.
* Use for cases where sizes of 0 and 1 are even slightly common.
*/
template<typename EntryType>
class nsCheapSet
{
public:
typedef typename EntryType::KeyType KeyType;
nsCheapSet() : mState(ZERO)
{
}
~nsCheapSet()
{
switch (mState) {
case ZERO:
break;
case ONE:
GetSingleEntry()->~EntryType();
break;
case MANY:
delete mUnion.table;
break;
default:
NS_NOTREACHED("bogus state");
break;
}
}
nsresult Put(const KeyType aVal);
void Remove(const KeyType aVal);
bool Contains(const KeyType aVal)
{
switch (mState) {
case ZERO:
return false;
case ONE:
return GetSingleEntry()->KeyEquals(EntryType::KeyToPointer(aVal));
case MANY:
return !!mUnion.table->GetEntry(aVal);
default:
NS_NOTREACHED("bogus state");
return false;
}
}
private:
EntryType* GetSingleEntry()
{
return reinterpret_cast<EntryType*>(&mUnion.singleEntry[0]);
}
enum SetState {
ZERO,
ONE,
MANY
};
union {
nsTHashtable<EntryType> *table;
char singleEntry[sizeof(EntryType)];
} mUnion;
enum SetState mState;
};
template<typename EntryType>
nsresult
nsCheapSet<EntryType>::Put(const KeyType aVal)
{
switch (mState) {
case ZERO:
new (GetSingleEntry()) EntryType(EntryType::KeyToPointer(aVal));
mState = ONE;
return NS_OK;
case ONE:
{
nsTHashtable<EntryType> *table = new nsTHashtable<EntryType>();
if (!table) {
return NS_ERROR_OUT_OF_MEMORY;
}
if (!table->Init()) {
return NS_ERROR_FAILURE;
}
EntryType *entry = GetSingleEntry();
if (!table->PutEntry(entry->GetKey())) {
return NS_ERROR_OUT_OF_MEMORY;
}
entry->~EntryType();
mUnion.table = table;
mState = MANY;
}
// Fall through.
case MANY:
if (!mUnion.table->PutEntry(aVal)) {
return NS_ERROR_OUT_OF_MEMORY;
}
return NS_OK;
default:
NS_NOTREACHED("bogus state");
return NS_OK;
}
}
template<typename EntryType>
void
nsCheapSet<EntryType>::Remove(const KeyType aVal)
{
switch (mState) {
case ZERO:
break;
case ONE:
if (Contains(aVal)) {
GetSingleEntry()->~EntryType();
mState = ZERO;
}
break;
case MANY:
mUnion.table->RemoveEntry(aVal);
break;
default:
NS_NOTREACHED("bogus state");
break;
}
}
#endif