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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) { mUnion.table = nullptr; }
~nsCheapSet() { Clear(); }
/**
* Remove all entries.
*/
void Clear() {
switch (mState) {
case ZERO:
break;
case ONE:
GetSingleEntry()->~EntryType();
break;
case MANY:
delete mUnion.table;
break;
default:
MOZ_ASSERT_UNREACHABLE("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:
MOZ_ASSERT_UNREACHABLE("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:
MOZ_ASSERT_UNREACHABLE("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;
}
[[fallthrough]];
case MANY:
mUnion.table->PutEntry(aVal);
return;
default:
MOZ_ASSERT_UNREACHABLE("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:
MOZ_ASSERT_UNREACHABLE("bogus state");
break;
}
}
#endif