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-rw-r--r--xpcom/ds/nsCheapSets.h171
1 files changed, 171 insertions, 0 deletions
diff --git a/xpcom/ds/nsCheapSets.h b/xpcom/ds/nsCheapSets.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef __nsCheapSets_h__
+#define __nsCheapSets_h__
+
+#include "nsTHashtable.h"
+#include <stdint.h>
+
+enum nsCheapSetOperator
+{
+ OpNext = 0, // enumerator says continue
+ OpRemove = 1, // enumerator says remove and continue
+};
+
+/**
+ * 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;
+ typedef nsCheapSetOperator (*Enumerator)(EntryType* aEntry, void* userArg);
+
+ nsCheapSet() : mState(ZERO) {}
+ ~nsCheapSet() { Clear(); }
+
+ /**
+ * Remove all entries.
+ */
+ void Clear()
+ {
+ switch (mState) {
+ case ZERO:
+ break;
+ case ONE:
+ GetSingleEntry()->~EntryType();
+ break;
+ case MANY:
+ delete mUnion.table;
+ break;
+ default:
+ NS_NOTREACHED("bogus state");
+ break;
+ }
+ mState = ZERO;
+ }
+
+ void 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;
+ }
+ }
+
+ uint32_t EnumerateEntries(Enumerator aEnumFunc, void* aUserArg)
+ {
+ switch (mState) {
+ case ZERO:
+ return 0;
+ case ONE:
+ if (aEnumFunc(GetSingleEntry(), aUserArg) == OpRemove) {
+ GetSingleEntry()->~EntryType();
+ mState = ZERO;
+ }
+ return 1;
+ case MANY: {
+ uint32_t n = mUnion.table->Count();
+ for (auto iter = mUnion.table->Iter(); !iter.Done(); iter.Next()) {
+ auto entry = static_cast<EntryType*>(iter.Get());
+ if (aEnumFunc(entry, aUserArg) == OpRemove) {
+ iter.Remove();
+ }
+ }
+ return n;
+ }
+ default:
+ NS_NOTREACHED("bogus state");
+ return 0;
+ }
+ }
+
+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>
+void
+nsCheapSet<EntryType>::Put(const KeyType aVal)
+{
+ switch (mState) {
+ case ZERO:
+ new (GetSingleEntry()) EntryType(EntryType::KeyToPointer(aVal));
+ mState = ONE;
+ return;
+ case ONE: {
+ nsTHashtable<EntryType>* table = new nsTHashtable<EntryType>();
+ EntryType* entry = GetSingleEntry();
+ table->PutEntry(entry->GetKey());
+ entry->~EntryType();
+ mUnion.table = table;
+ mState = MANY;
+ }
+ MOZ_FALLTHROUGH;
+
+ case MANY:
+ mUnion.table->PutEntry(aVal);
+ return;
+ default:
+ NS_NOTREACHED("bogus state");
+ return;
+ }
+}
+
+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