mirror of
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135 lines
2.7 KiB
C++
135 lines
2.7 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef __nsCheapSets_h__
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#define __nsCheapSets_h__
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#include "nsTHashtable.h"
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#include "mozilla/StandardInteger.h"
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/**
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* A set that takes up minimal size when there are 0 or 1 entries in the set.
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* Use for cases where sizes of 0 and 1 are even slightly common.
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*/
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template<typename EntryType>
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class nsCheapSet
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{
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public:
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typedef typename EntryType::KeyType KeyType;
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nsCheapSet() : mState(ZERO)
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{
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}
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~nsCheapSet()
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{
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switch (mState) {
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case ZERO:
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break;
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case ONE:
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GetSingleEntry()->~EntryType();
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break;
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case MANY:
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delete mUnion.table;
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break;
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default:
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NS_NOTREACHED("bogus state");
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break;
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}
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}
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nsresult Put(const KeyType aVal);
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void Remove(const KeyType aVal);
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bool Contains(const KeyType aVal)
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{
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switch (mState) {
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case ZERO:
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return false;
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case ONE:
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return GetSingleEntry()->KeyEquals(EntryType::KeyToPointer(aVal));
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case MANY:
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return !!mUnion.table->GetEntry(aVal);
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default:
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NS_NOTREACHED("bogus state");
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return false;
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}
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}
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private:
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EntryType* GetSingleEntry()
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{
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return reinterpret_cast<EntryType*>(&mUnion.singleEntry[0]);
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}
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enum SetState {
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ZERO,
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ONE,
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MANY
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};
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union {
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nsTHashtable<EntryType> *table;
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char singleEntry[sizeof(EntryType)];
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} mUnion;
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enum SetState mState;
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};
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template<typename EntryType>
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nsresult
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nsCheapSet<EntryType>::Put(const KeyType aVal)
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{
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switch (mState) {
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case ZERO:
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new (GetSingleEntry()) EntryType(EntryType::KeyToPointer(aVal));
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mState = ONE;
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return NS_OK;
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case ONE:
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{
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nsTHashtable<EntryType> *table = new nsTHashtable<EntryType>();
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if (!table) {
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return NS_ERROR_OUT_OF_MEMORY;
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}
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table->Init();
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EntryType *entry = GetSingleEntry();
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table->PutEntry(entry->GetKey());
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entry->~EntryType();
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mUnion.table = table;
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mState = MANY;
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}
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// Fall through.
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case MANY:
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mUnion.table->PutEntry(aVal);
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return NS_OK;
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default:
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NS_NOTREACHED("bogus state");
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return NS_OK;
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}
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}
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template<typename EntryType>
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void
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nsCheapSet<EntryType>::Remove(const KeyType aVal)
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{
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switch (mState) {
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case ZERO:
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break;
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case ONE:
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if (Contains(aVal)) {
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GetSingleEntry()->~EntryType();
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mState = ZERO;
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}
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break;
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case MANY:
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mUnion.table->RemoveEntry(aVal);
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break;
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default:
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NS_NOTREACHED("bogus state");
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break;
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}
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}
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#endif
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