js/public/HashTable.h
author Nicholas Nethercote <nnethercote@mozilla.com>
Wed, 16 Jul 2014 16:51:09 -0700
changeset 216448 8cf3f3b925a362186c6cdf408a46aa539d895db2
parent 215455 91d7659bb35145e10ff737753688e0972c1a79b5
child 221612 70803a5f468399d53409b9c3e1df441ed02d1282
permissions -rw-r--r--
Bug 1038601 - Shrink js::HashTable. r=luke. This patch reduces sizeof(js::HashTable): - On 64-bit: from 32 bytes to 24 bytes. - On 32-bit: from 24 bytes to 16 bytes. The latter is particularly nice because jemalloc rounds up allocation requests of 24 bytes to 32, but it can allocate 16 bytes without slop, so we're saving 16 bytes per heap-allocated HashTable. This is done by: - Shrinking |removedCount| and |hashShift|. - Reordering the fields. - Not defining |mutationCount| and |mEntered| in non-DEBUG builds rather than using DebugOnly<> -- in non-DEBUG builds, DebugOnly<> fields take up 1 byte each. This change saves over 55 KiB when starting Firefox and loading Gmail. The patch also uses uint32_t more consistently for the generation.

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * 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 js_HashTable_h
#define js_HashTable_h

#include "mozilla/Alignment.h"
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/Casting.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Move.h"
#include "mozilla/NullPtr.h"
#include "mozilla/PodOperations.h"
#include "mozilla/ReentrancyGuard.h"
#include "mozilla/TemplateLib.h"
#include "mozilla/TypeTraits.h"

#include "js/Utility.h"

namespace js {

class TempAllocPolicy;
template <class> struct DefaultHasher;
template <class, class> class HashMapEntry;
namespace detail {
    template <class T> class HashTableEntry;
    template <class T, class HashPolicy, class AllocPolicy> class HashTable;
}

/*****************************************************************************/

// A JS-friendly, STL-like container providing a hash-based map from keys to
// values. In particular, HashMap calls constructors and destructors of all
// objects added so non-PODs may be used safely.
//
// Key/Value requirements:
//  - movable, destructible, assignable
// HashPolicy requirements:
//  - see Hash Policy section below
// AllocPolicy:
//  - see jsalloc.h
//
// Note:
// - HashMap is not reentrant: Key/Value/HashPolicy/AllocPolicy members
//   called by HashMap must not call back into the same HashMap object.
// - Due to the lack of exception handling, the user must call |init()|.
template <class Key,
          class Value,
          class HashPolicy = DefaultHasher<Key>,
          class AllocPolicy = TempAllocPolicy>
class HashMap
{
    typedef HashMapEntry<Key, Value> TableEntry;

    struct MapHashPolicy : HashPolicy
    {
        typedef Key KeyType;
        static const Key &getKey(TableEntry &e) { return e.key(); }
        static void setKey(TableEntry &e, Key &k) { HashPolicy::rekey(e.mutableKey(), k); }
    };

    typedef detail::HashTable<TableEntry, MapHashPolicy, AllocPolicy> Impl;
    Impl impl;

  public:
    typedef typename HashPolicy::Lookup Lookup;
    typedef TableEntry Entry;

    // HashMap construction is fallible (due to OOM); thus the user must call
    // init after constructing a HashMap and check the return value.
    explicit HashMap(AllocPolicy a = AllocPolicy()) : impl(a)  {}
    bool init(uint32_t len = 16)                      { return impl.init(len); }
    bool initialized() const                          { return impl.initialized(); }

    // Return whether the given lookup value is present in the map. E.g.:
    //
    //   typedef HashMap<int,char> HM;
    //   HM h;
    //   if (HM::Ptr p = h.lookup(3)) {
    //     const HM::Entry &e = *p; // p acts like a pointer to Entry
    //     assert(p->key == 3);     // Entry contains the key
    //     char val = p->value;     // and value
    //   }
    //
    // Also see the definition of Ptr in HashTable above (with T = Entry).
    typedef typename Impl::Ptr Ptr;
    Ptr lookup(const Lookup &l) const                 { return impl.lookup(l); }

    // Like lookup, but does not assert if two threads call lookup at the same
    // time. Only use this method when none of the threads will modify the map.
    Ptr readonlyThreadsafeLookup(const Lookup &l) const { return impl.readonlyThreadsafeLookup(l); }

    // Assuming |p.found()|, remove |*p|.
    void remove(Ptr p)                                { impl.remove(p); }

    // Like |lookup(l)|, but on miss, |p = lookupForAdd(l)| allows efficient
    // insertion of Key |k| (where |HashPolicy::match(k,l) == true|) using
    // |add(p,k,v)|. After |add(p,k,v)|, |p| points to the new Entry. E.g.:
    //
    //   typedef HashMap<int,char> HM;
    //   HM h;
    //   HM::AddPtr p = h.lookupForAdd(3);
    //   if (!p) {
    //     if (!h.add(p, 3, 'a'))
    //       return false;
    //   }
    //   const HM::Entry &e = *p;   // p acts like a pointer to Entry
    //   assert(p->key == 3);       // Entry contains the key
    //   char val = p->value;       // and value
    //
    // Also see the definition of AddPtr in HashTable above (with T = Entry).
    //
    // N.B. The caller must ensure that no mutating hash table operations
    // occur between a pair of |lookupForAdd| and |add| calls. To avoid
    // looking up the key a second time, the caller may use the more efficient
    // relookupOrAdd method. This method reuses part of the hashing computation
    // to more efficiently insert the key if it has not been added. For
    // example, a mutation-handling version of the previous example:
    //
    //    HM::AddPtr p = h.lookupForAdd(3);
    //    if (!p) {
    //      call_that_may_mutate_h();
    //      if (!h.relookupOrAdd(p, 3, 'a'))
    //        return false;
    //    }
    //    const HM::Entry &e = *p;
    //    assert(p->key == 3);
    //    char val = p->value;
    typedef typename Impl::AddPtr AddPtr;
    AddPtr lookupForAdd(const Lookup &l) const {
        return impl.lookupForAdd(l);
    }

    template<typename KeyInput, typename ValueInput>
    bool add(AddPtr &p, KeyInput &&k, ValueInput &&v) {
        Entry e(mozilla::Forward<KeyInput>(k), mozilla::Forward<ValueInput>(v));
        return impl.add(p, mozilla::Move(e));
    }

    template<typename KeyInput>
    bool add(AddPtr &p, KeyInput &&k) {
        Entry e(mozilla::Forward<KeyInput>(k), Value());
        return impl.add(p, mozilla::Move(e));
    }

    template<typename KeyInput, typename ValueInput>
    bool relookupOrAdd(AddPtr &p, KeyInput &&k, ValueInput &&v) {
        Entry e(mozilla::Forward<KeyInput>(k), mozilla::Forward<ValueInput>(v));
        return impl.relookupOrAdd(p, e.key(), mozilla::Move(e));
    }

    // |all()| returns a Range containing |count()| elements. E.g.:
    //
    //   typedef HashMap<int,char> HM;
    //   HM h;
    //   for (HM::Range r = h.all(); !r.empty(); r.popFront())
    //     char c = r.front().value();
    //
    // Also see the definition of Range in HashTable above (with T = Entry).
    typedef typename Impl::Range Range;
    Range all() const                                 { return impl.all(); }

    // Typedef for the enumeration class. An Enum may be used to examine and
    // remove table entries:
    //
    //   typedef HashMap<int,char> HM;
    //   HM s;
    //   for (HM::Enum e(s); !e.empty(); e.popFront())
    //     if (e.front().value() == 'l')
    //       e.removeFront();
    //
    // Table resize may occur in Enum's destructor. Also see the definition of
    // Enum in HashTable above (with T = Entry).
    typedef typename Impl::Enum Enum;

    // Remove all entries. This does not shrink the table. For that consider
    // using the finish() method.
    void clear()                                      { impl.clear(); }

    // Remove all the entries and release all internal buffers. The map must
    // be initialized again before any use.
    void finish()                                     { impl.finish(); }

    // Does the table contain any entries?
    bool empty() const                                { return impl.empty(); }

    // Number of live elements in the map.
    uint32_t count() const                            { return impl.count(); }

    // Total number of allocation in the dynamic table. Note: resize will
    // happen well before count() == capacity().
    size_t capacity() const                           { return impl.capacity(); }

    // Don't just call |impl.sizeOfExcludingThis()| because there's no
    // guarantee that |impl| is the first field in HashMap.
    size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
        return impl.sizeOfExcludingThis(mallocSizeOf);
    }
    size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
        return mallocSizeOf(this) + impl.sizeOfExcludingThis(mallocSizeOf);
    }

    // If |generation()| is the same before and after a HashMap operation,
    // pointers into the table remain valid.
    uint32_t generation() const                       { return impl.generation(); }

    /************************************************** Shorthand operations */

    bool has(const Lookup &l) const {
        return impl.lookup(l) != nullptr;
    }

    // Overwrite existing value with v. Return false on oom.
    template<typename KeyInput, typename ValueInput>
    bool put(KeyInput &&k, ValueInput &&v) {
        AddPtr p = lookupForAdd(k);
        if (p) {
            p->value() = mozilla::Forward<ValueInput>(v);
            return true;
        }
        return add(p, mozilla::Forward<KeyInput>(k), mozilla::Forward<ValueInput>(v));
    }

    // Like put, but assert that the given key is not already present.
    template<typename KeyInput, typename ValueInput>
    bool putNew(KeyInput &&k, ValueInput &&v) {
        Entry e(mozilla::Forward<KeyInput>(k), mozilla::Forward<ValueInput>(v));
        return impl.putNew(e.key(), mozilla::Move(e));
    }

    // Add (k,defaultValue) if |k| is not found. Return a false-y Ptr on oom.
    Ptr lookupWithDefault(const Key &k, const Value &defaultValue) {
        AddPtr p = lookupForAdd(k);
        if (p)
            return p;
        (void)add(p, k, defaultValue);  // p is left false-y on oom.
        return p;
    }

    // Remove if present.
    void remove(const Lookup &l) {
        if (Ptr p = lookup(l))
            remove(p);
    }

    // Infallibly rekey one entry, if necessary.
    // Requires template parameters Key and HashPolicy::Lookup to be the same type.
    void rekeyIfMoved(const Key &old_key, const Key &new_key) {
        if (old_key != new_key)
            rekeyAs(old_key, new_key, new_key);
    }

    // Infallibly rekey one entry, if present.
    void rekeyAs(const Lookup &old_lookup, const Lookup &new_lookup, const Key &new_key) {
        if (Ptr p = lookup(old_lookup))
            impl.rekeyAndMaybeRehash(p, new_lookup, new_key);
    }

    // HashMap is movable
    HashMap(HashMap &&rhs) : impl(mozilla::Move(rhs.impl)) {}
    void operator=(HashMap &&rhs) {
        MOZ_ASSERT(this != &rhs, "self-move assignment is prohibited");
        impl = mozilla::Move(rhs.impl);
    }

  private:
    // HashMap is not copyable or assignable
    HashMap(const HashMap &hm) MOZ_DELETE;
    HashMap &operator=(const HashMap &hm) MOZ_DELETE;

    friend class Impl::Enum;
};

/*****************************************************************************/

// A JS-friendly, STL-like container providing a hash-based set of values. In
// particular, HashSet calls constructors and destructors of all objects added
// so non-PODs may be used safely.
//
// T requirements:
//  - movable, destructible, assignable
// HashPolicy requirements:
//  - see Hash Policy section below
// AllocPolicy:
//  - see jsalloc.h
//
// Note:
// - HashSet is not reentrant: T/HashPolicy/AllocPolicy members called by
//   HashSet must not call back into the same HashSet object.
// - Due to the lack of exception handling, the user must call |init()|.
template <class T,
          class HashPolicy = DefaultHasher<T>,
          class AllocPolicy = TempAllocPolicy>
class HashSet
{
    struct SetOps : HashPolicy
    {
        typedef T KeyType;
        static const KeyType &getKey(const T &t) { return t; }
        static void setKey(T &t, KeyType &k) { HashPolicy::rekey(t, k); }
    };

    typedef detail::HashTable<const T, SetOps, AllocPolicy> Impl;
    Impl impl;

  public:
    typedef typename HashPolicy::Lookup Lookup;
    typedef T Entry;

    // HashSet construction is fallible (due to OOM); thus the user must call
    // init after constructing a HashSet and check the return value.
    explicit HashSet(AllocPolicy a = AllocPolicy()) : impl(a)  {}
    bool init(uint32_t len = 16)                      { return impl.init(len); }
    bool initialized() const                          { return impl.initialized(); }

    // Return whether the given lookup value is present in the map. E.g.:
    //
    //   typedef HashSet<int> HS;
    //   HS h;
    //   if (HS::Ptr p = h.lookup(3)) {
    //     assert(*p == 3);   // p acts like a pointer to int
    //   }
    //
    // Also see the definition of Ptr in HashTable above.
    typedef typename Impl::Ptr Ptr;
    Ptr lookup(const Lookup &l) const                 { return impl.lookup(l); }

    // Like lookup, but does not assert if two threads call lookup at the same
    // time. Only use this method when none of the threads will modify the map.
    Ptr readonlyThreadsafeLookup(const Lookup &l) const { return impl.readonlyThreadsafeLookup(l); }

    // Assuming |p.found()|, remove |*p|.
    void remove(Ptr p)                                { impl.remove(p); }

    // Like |lookup(l)|, but on miss, |p = lookupForAdd(l)| allows efficient
    // insertion of T value |t| (where |HashPolicy::match(t,l) == true|) using
    // |add(p,t)|. After |add(p,t)|, |p| points to the new element. E.g.:
    //
    //   typedef HashSet<int> HS;
    //   HS h;
    //   HS::AddPtr p = h.lookupForAdd(3);
    //   if (!p) {
    //     if (!h.add(p, 3))
    //       return false;
    //   }
    //   assert(*p == 3);   // p acts like a pointer to int
    //
    // Also see the definition of AddPtr in HashTable above.
    //
    // N.B. The caller must ensure that no mutating hash table operations
    // occur between a pair of |lookupForAdd| and |add| calls. To avoid
    // looking up the key a second time, the caller may use the more efficient
    // relookupOrAdd method. This method reuses part of the hashing computation
    // to more efficiently insert the key if it has not been added. For
    // example, a mutation-handling version of the previous example:
    //
    //    HS::AddPtr p = h.lookupForAdd(3);
    //    if (!p) {
    //      call_that_may_mutate_h();
    //      if (!h.relookupOrAdd(p, 3, 3))
    //        return false;
    //    }
    //    assert(*p == 3);
    //
    // Note that relookupOrAdd(p,l,t) performs Lookup using |l| and adds the
    // entry |t|, where the caller ensures match(l,t).
    typedef typename Impl::AddPtr AddPtr;
    AddPtr lookupForAdd(const Lookup &l) const        { return impl.lookupForAdd(l); }

    template <typename U>
    bool add(AddPtr &p, U &&u) {
        return impl.add(p, mozilla::Forward<U>(u));
    }

    template <typename U>
    bool relookupOrAdd(AddPtr &p, const Lookup &l, U &&u) {
        return impl.relookupOrAdd(p, l, mozilla::Forward<U>(u));
    }

    // |all()| returns a Range containing |count()| elements:
    //
    //   typedef HashSet<int> HS;
    //   HS h;
    //   for (HS::Range r = h.all(); !r.empty(); r.popFront())
    //     int i = r.front();
    //
    // Also see the definition of Range in HashTable above.
    typedef typename Impl::Range Range;
    Range all() const                                 { return impl.all(); }

    // Typedef for the enumeration class. An Enum may be used to examine and
    // remove table entries:
    //
    //   typedef HashSet<int> HS;
    //   HS s;
    //   for (HS::Enum e(s); !e.empty(); e.popFront())
    //     if (e.front() == 42)
    //       e.removeFront();
    //
    // Table resize may occur in Enum's destructor. Also see the definition of
    // Enum in HashTable above.
    typedef typename Impl::Enum Enum;

    // Remove all entries. This does not shrink the table. For that consider
    // using the finish() method.
    void clear()                                      { impl.clear(); }

    // Remove all the entries and release all internal buffers. The set must
    // be initialized again before any use.
    void finish()                                     { impl.finish(); }

    // Does the table contain any entries?
    bool empty() const                                { return impl.empty(); }

    // Number of live elements in the map.
    uint32_t count() const                            { return impl.count(); }

    // Total number of allocation in the dynamic table. Note: resize will
    // happen well before count() == capacity().
    size_t capacity() const                           { return impl.capacity(); }

    // Don't just call |impl.sizeOfExcludingThis()| because there's no
    // guarantee that |impl| is the first field in HashSet.
    size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
        return impl.sizeOfExcludingThis(mallocSizeOf);
    }
    size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
        return mallocSizeOf(this) + impl.sizeOfExcludingThis(mallocSizeOf);
    }

    // If |generation()| is the same before and after a HashSet operation,
    // pointers into the table remain valid.
    uint32_t generation() const                       { return impl.generation(); }

    /************************************************** Shorthand operations */

    bool has(const Lookup &l) const {
        return impl.lookup(l) != nullptr;
    }

    // Add |u| if it is not present already. Return false on oom.
    template <typename U>
    bool put(U &&u) {
        AddPtr p = lookupForAdd(u);
        return p ? true : add(p, mozilla::Forward<U>(u));
    }

    // Like put, but assert that the given key is not already present.
    template <typename U>
    bool putNew(U &&u) {
        return impl.putNew(u, mozilla::Forward<U>(u));
    }

    template <typename U>
    bool putNew(const Lookup &l, U &&u) {
        return impl.putNew(l, mozilla::Forward<U>(u));
    }

    void remove(const Lookup &l) {
        if (Ptr p = lookup(l))
            remove(p);
    }

    // Infallibly rekey one entry, if present.
    // Requires template parameters T and HashPolicy::Lookup to be the same type.
    void rekeyIfMoved(const Lookup &old_value, const T &new_value) {
        if (old_value != new_value)
            rekeyAs(old_value, new_value, new_value);
    }

    // Infallibly rekey one entry, if present.
    void rekeyAs(const Lookup &old_lookup, const Lookup &new_lookup, const T &new_value) {
        if (Ptr p = lookup(old_lookup))
            impl.rekeyAndMaybeRehash(p, new_lookup, new_value);
    }

    // Infallibly rekey one entry with a new key that is equivalent.
    void rekeyInPlace(Ptr p, const T &new_value)
    {
        MOZ_ASSERT(HashPolicy::match(*p, new_value));
        impl.rekeyInPlace(p, new_value);
    }

    // HashSet is movable
    HashSet(HashSet &&rhs) : impl(mozilla::Move(rhs.impl)) {}
    void operator=(HashSet &&rhs) {
        MOZ_ASSERT(this != &rhs, "self-move assignment is prohibited");
        impl = mozilla::Move(rhs.impl);
    }

  private:
    // HashSet is not copyable or assignable
    HashSet(const HashSet &hs) MOZ_DELETE;
    HashSet &operator=(const HashSet &hs) MOZ_DELETE;

    friend class Impl::Enum;
};

/*****************************************************************************/

// Hash Policy
//
// A hash policy P for a hash table with key-type Key must provide:
//  - a type |P::Lookup| to use to lookup table entries;
//  - a static member function |P::hash| with signature
//
//      static js::HashNumber hash(Lookup)
//
//    to use to hash the lookup type; and
//  - a static member function |P::match| with signature
//
//      static bool match(Key, Lookup)
//
//    to use to test equality of key and lookup values.
//
// Normally, Lookup = Key. In general, though, different values and types of
// values can be used to lookup and store. If a Lookup value |l| is != to the
// added Key value |k|, the user must ensure that |P::match(k,l)|. E.g.:
//
//   js::HashSet<Key, P>::AddPtr p = h.lookup(l);
//   if (!p) {
//     assert(P::match(k, l));  // must hold
//     h.add(p, k);
//   }

// Pointer hashing policy that strips the lowest zeroBits when calculating the
// hash to improve key distribution.
template <typename Key, size_t zeroBits>
struct PointerHasher
{
    typedef Key Lookup;
    static HashNumber hash(const Lookup &l) {
        MOZ_ASSERT(!JS::IsPoisonedPtr(l));
        size_t word = reinterpret_cast<size_t>(l) >> zeroBits;
        JS_STATIC_ASSERT(sizeof(HashNumber) == 4);
#if JS_BITS_PER_WORD == 32
        return HashNumber(word);
#else
        JS_STATIC_ASSERT(sizeof word == 8);
        return HashNumber((word >> 32) ^ word);
#endif
    }
    static bool match(const Key &k, const Lookup &l) {
        MOZ_ASSERT(!JS::IsPoisonedPtr(k));
        MOZ_ASSERT(!JS::IsPoisonedPtr(l));
        return k == l;
    }
    static void rekey(Key &k, const Key& newKey) {
        k = newKey;
    }
};

// Default hash policy: just use the 'lookup' value. This of course only
// works if the lookup value is integral. HashTable applies ScrambleHashCode to
// the result of the 'hash' which means that it is 'ok' if the lookup value is
// not well distributed over the HashNumber domain.
template <class Key>
struct DefaultHasher
{
    typedef Key Lookup;
    static HashNumber hash(const Lookup &l) {
        // Hash if can implicitly cast to hash number type.
        return l;
    }
    static bool match(const Key &k, const Lookup &l) {
        // Use builtin or overloaded operator==.
        return k == l;
    }
    static void rekey(Key &k, const Key& newKey) {
        k = newKey;
    }
};

// Specialize hashing policy for pointer types. It assumes that the type is
// at least word-aligned. For types with smaller size use PointerHasher.
template <class T>
struct DefaultHasher<T *> : PointerHasher<T *, mozilla::tl::FloorLog2<sizeof(void *)>::value>
{};

// For doubles, we can xor the two uint32s.
template <>
struct DefaultHasher<double>
{
    typedef double Lookup;
    static HashNumber hash(double d) {
        JS_STATIC_ASSERT(sizeof(HashNumber) == 4);
        uint64_t u = mozilla::BitwiseCast<uint64_t>(d);
        return HashNumber(u ^ (u >> 32));
    }
    static bool match(double lhs, double rhs) {
        return mozilla::BitwiseCast<uint64_t>(lhs) == mozilla::BitwiseCast<uint64_t>(rhs);
    }
};

template <>
struct DefaultHasher<float>
{
    typedef float Lookup;
    static HashNumber hash(float f) {
        JS_STATIC_ASSERT(sizeof(HashNumber) == 4);
        return HashNumber(mozilla::BitwiseCast<uint32_t>(f));
    }
    static bool match(float lhs, float rhs) {
        return mozilla::BitwiseCast<uint32_t>(lhs) == mozilla::BitwiseCast<uint32_t>(rhs);
    }
};

/*****************************************************************************/

// Both HashMap and HashSet are implemented by a single HashTable that is even
// more heavily parameterized than the other two. This leaves HashTable gnarly
// and extremely coupled to HashMap and HashSet; thus code should not use
// HashTable directly.

template <class Key, class Value>
class HashMapEntry
{
    Key key_;
    Value value_;

    template <class, class, class> friend class detail::HashTable;
    template <class> friend class detail::HashTableEntry;
    template <class, class, class, class> friend class HashMap;

    Key & mutableKey() { return key_; }

  public:
    template<typename KeyInput, typename ValueInput>
    HashMapEntry(KeyInput &&k, ValueInput &&v)
      : key_(mozilla::Forward<KeyInput>(k)),
        value_(mozilla::Forward<ValueInput>(v))
    {}

    HashMapEntry(HashMapEntry &&rhs)
      : key_(mozilla::Move(rhs.key_)),
        value_(mozilla::Move(rhs.value_))
    {}

    typedef Key KeyType;
    typedef Value ValueType;

    const Key & key() const { return key_; }
    const Value & value() const { return value_; }
    Value & value() { return value_; }

  private:
    HashMapEntry(const HashMapEntry &) MOZ_DELETE;
    void operator=(const HashMapEntry &) MOZ_DELETE;
};

} // namespace js

namespace mozilla {

template <typename T>
struct IsPod<js::detail::HashTableEntry<T> > : IsPod<T> {};

template <typename K, typename V>
struct IsPod<js::HashMapEntry<K, V> >
  : IntegralConstant<bool, IsPod<K>::value && IsPod<V>::value>
{};

} // namespace mozilla

namespace js {

namespace detail {

template <class T, class HashPolicy, class AllocPolicy>
class HashTable;

template <class T>
class HashTableEntry
{
    template <class, class, class> friend class HashTable;
    typedef typename mozilla::RemoveConst<T>::Type NonConstT;

    HashNumber keyHash;
    mozilla::AlignedStorage2<NonConstT> mem;

    static const HashNumber sFreeKey = 0;
    static const HashNumber sRemovedKey = 1;
    static const HashNumber sCollisionBit = 1;

    static bool isLiveHash(HashNumber hash)
    {
        return hash > sRemovedKey;
    }

    HashTableEntry(const HashTableEntry &) MOZ_DELETE;
    void operator=(const HashTableEntry &) MOZ_DELETE;
    ~HashTableEntry() MOZ_DELETE;

  public:
    // NB: HashTableEntry is treated as a POD: no constructor or destructor calls.

    void destroyIfLive() {
        if (isLive())
            mem.addr()->~T();
    }

    void destroy() {
        MOZ_ASSERT(isLive());
        mem.addr()->~T();
    }

    void swap(HashTableEntry *other) {
        mozilla::Swap(keyHash, other->keyHash);
        mozilla::Swap(mem, other->mem);
    }

    T &get() { MOZ_ASSERT(isLive()); return *mem.addr(); }

    bool isFree() const    { return keyHash == sFreeKey; }
    void clearLive()       { MOZ_ASSERT(isLive()); keyHash = sFreeKey; mem.addr()->~T(); }
    void clear()           { if (isLive()) mem.addr()->~T(); keyHash = sFreeKey; }
    bool isRemoved() const { return keyHash == sRemovedKey; }
    void removeLive()      { MOZ_ASSERT(isLive()); keyHash = sRemovedKey; mem.addr()->~T(); }
    bool isLive() const    { return isLiveHash(keyHash); }
    void setCollision()               { MOZ_ASSERT(isLive()); keyHash |= sCollisionBit; }
    void setCollision(HashNumber bit) { MOZ_ASSERT(isLive()); keyHash |= bit; }
    void unsetCollision()             { keyHash &= ~sCollisionBit; }
    bool hasCollision() const         { return keyHash & sCollisionBit; }
    bool matchHash(HashNumber hn)     { return (keyHash & ~sCollisionBit) == hn; }
    HashNumber getKeyHash() const     { return keyHash & ~sCollisionBit; }

    template <class U>
    void setLive(HashNumber hn, U &&u)
    {
        MOZ_ASSERT(!isLive());
        keyHash = hn;
        new(mem.addr()) T(mozilla::Forward<U>(u));
        MOZ_ASSERT(isLive());
    }
};

template <class T, class HashPolicy, class AllocPolicy>
class HashTable : private AllocPolicy
{
    friend class mozilla::ReentrancyGuard;

    typedef typename mozilla::RemoveConst<T>::Type NonConstT;
    typedef typename HashPolicy::KeyType Key;
    typedef typename HashPolicy::Lookup Lookup;

  public:
    typedef HashTableEntry<T> Entry;

    // A nullable pointer to a hash table element. A Ptr |p| can be tested
    // either explicitly |if (p.found()) p->...| or using boolean conversion
    // |if (p) p->...|. Ptr objects must not be used after any mutating hash
    // table operations unless |generation()| is tested.
    class Ptr
    {
        friend class HashTable;
        typedef void (Ptr::* ConvertibleToBool)();
        void nonNull() {}

        Entry *entry_;
#ifdef DEBUG
        const HashTable *table_;
        uint32_t generation;
#endif

      protected:
        Ptr(Entry &entry, const HashTable &tableArg)
          : entry_(&entry)
#ifdef DEBUG
          , table_(&tableArg)
          , generation(tableArg.generation())
#endif
        {}

      public:
        // Leaves Ptr uninitialized.
        Ptr() {
#ifdef JS_DEBUG
            entry_ = (Entry *)0xbad;
#endif
        }

        bool found() const {
            MOZ_ASSERT(generation == table_->generation());
            return entry_->isLive();
        }

        operator ConvertibleToBool() const {
            return found() ? &Ptr::nonNull : 0;
        }

        bool operator==(const Ptr &rhs) const {
            MOZ_ASSERT(found() && rhs.found());
            return entry_ == rhs.entry_;
        }

        bool operator!=(const Ptr &rhs) const {
            MOZ_ASSERT(generation == table_->generation());
            return !(*this == rhs);
        }

        T &operator*() const {
            MOZ_ASSERT(generation == table_->generation());
            return entry_->get();
        }

        T *operator->() const {
            MOZ_ASSERT(generation == table_->generation());
            return &entry_->get();
        }
    };

    // A Ptr that can be used to add a key after a failed lookup.
    class AddPtr : public Ptr
    {
        friend class HashTable;
        HashNumber keyHash;
#ifdef DEBUG
        uint64_t mutationCount;
#endif

        AddPtr(Entry &entry, const HashTable &tableArg, HashNumber hn)
          : Ptr(entry, tableArg)
          , keyHash(hn)
#ifdef DEBUG
          , mutationCount(tableArg.mutationCount)
#endif
        {}

      public:
        // Leaves AddPtr uninitialized.
        AddPtr() {}
    };

    // A collection of hash table entries. The collection is enumerated by
    // calling |front()| followed by |popFront()| as long as |!empty()|. As
    // with Ptr/AddPtr, Range objects must not be used after any mutating hash
    // table operation unless the |generation()| is tested.
    class Range
    {
      protected:
        friend class HashTable;

        Range(const HashTable &tableArg, Entry *c, Entry *e)
          : cur(c)
          , end(e)
#ifdef DEBUG
          , table_(&tableArg)
          , mutationCount(tableArg.mutationCount)
          , generation(tableArg.generation())
          , validEntry(true)
#endif
        {
            while (cur < end && !cur->isLive())
                ++cur;
        }

        Entry *cur, *end;
#ifdef DEBUG
        const HashTable *table_;
        uint64_t mutationCount;
        uint32_t generation;
        bool validEntry;
#endif

      public:
        Range()
          : cur(nullptr)
          , end(nullptr)
#ifdef DEBUG
          , table_(nullptr)
          , mutationCount(0)
          , generation(0)
          , validEntry(false)
#endif
        {}

        bool empty() const {
            MOZ_ASSERT(generation == table_->generation());
            MOZ_ASSERT(mutationCount == table_->mutationCount);
            return cur == end;
        }

        T &front() const {
            MOZ_ASSERT(validEntry);
            MOZ_ASSERT(!empty());
            MOZ_ASSERT(generation == table_->generation());
            MOZ_ASSERT(mutationCount == table_->mutationCount);
            return cur->get();
        }

        void popFront() {
            MOZ_ASSERT(!empty());
            MOZ_ASSERT(generation == table_->generation());
            MOZ_ASSERT(mutationCount == table_->mutationCount);
            while (++cur < end && !cur->isLive())
                continue;
#ifdef DEBUG
            validEntry = true;
#endif
        }
    };

    // A Range whose lifetime delimits a mutating enumeration of a hash table.
    // Since rehashing when elements were removed during enumeration would be
    // bad, it is postponed until the Enum is destructed.  Since the Enum's
    // destructor touches the hash table, the user must ensure that the hash
    // table is still alive when the destructor runs.
    class Enum : public Range
    {
        friend class HashTable;

        HashTable &table_;
        bool rekeyed;
        bool removed;

        /* Not copyable. */
        Enum(const Enum &) MOZ_DELETE;
        void operator=(const Enum &) MOZ_DELETE;

      public:
        template<class Map> explicit
        Enum(Map &map) : Range(map.all()), table_(map.impl), rekeyed(false), removed(false) {}

        // Removes the |front()| element from the table, leaving |front()|
        // invalid until the next call to |popFront()|. For example:
        //
        //   HashSet<int> s;
        //   for (HashSet<int>::Enum e(s); !e.empty(); e.popFront())
        //     if (e.front() == 42)
        //       e.removeFront();
        void removeFront() {
            table_.remove(*this->cur);
            removed = true;
#ifdef DEBUG
            this->validEntry = false;
            this->mutationCount = table_.mutationCount;
#endif
        }

        // Removes the |front()| element and re-inserts it into the table with
        // a new key at the new Lookup position.  |front()| is invalid after
        // this operation until the next call to |popFront()|.
        void rekeyFront(const Lookup &l, const Key &k) {
            Ptr p(*this->cur, table_);
            table_.rekeyWithoutRehash(p, l, k);
            rekeyed = true;
#ifdef DEBUG
            this->validEntry = false;
            this->mutationCount = table_.mutationCount;
#endif
        }

        void rekeyFront(const Key &k) {
            rekeyFront(k, k);
        }

        // Potentially rehashes the table.
        ~Enum() {
            if (rekeyed) {
                table_.gen++;
                table_.checkOverRemoved();
            }

            if (removed)
                table_.compactIfUnderloaded();
        }
    };

    // HashTable is movable
    HashTable(HashTable &&rhs)
      : AllocPolicy(rhs)
    {
        mozilla::PodAssign(this, &rhs);
        rhs.table = nullptr;
    }
    void operator=(HashTable &&rhs) {
        MOZ_ASSERT(this != &rhs, "self-move assignment is prohibited");
        if (table)
            destroyTable(*this, table, capacity());
        mozilla::PodAssign(this, &rhs);
        rhs.table = nullptr;
    }

  private:
    // HashTable is not copyable or assignable
    HashTable(const HashTable &) MOZ_DELETE;
    void operator=(const HashTable &) MOZ_DELETE;

  private:
    static const size_t CAP_BITS = 24;

  public:
    Entry       *table;                 // entry storage
    uint32_t    gen;                    // entry storage generation number
    uint32_t    entryCount;             // number of entries in table
    uint32_t    removedCount:CAP_BITS;  // removed entry sentinels in table
    uint32_t    hashShift:8;            // multiplicative hash shift

#ifdef JS_DEBUG
    mozilla::DebugOnly<uint64_t>     mutationCount;
    mutable mozilla::DebugOnly<bool> mEntered;
    mutable struct Stats
    {
        uint32_t        searches;       // total number of table searches
        uint32_t        steps;          // hash chain links traversed
        uint32_t        hits;           // searches that found key
        uint32_t        misses;         // searches that didn't find key
        uint32_t        addOverRemoved; // adds that recycled a removed entry
        uint32_t        removes;        // calls to remove
        uint32_t        removeFrees;    // calls to remove that freed the entry
        uint32_t        grows;          // table expansions
        uint32_t        shrinks;        // table contractions
        uint32_t        compresses;     // table compressions
        uint32_t        rehashes;       // tombstone decontaminations
    } stats;
#   define METER(x) x
#else
#   define METER(x)
#endif

    // The default initial capacity is 32 (enough to hold 16 elements), but it
    // can be as low as 4.
    static const unsigned sMinCapacityLog2 = 2;
    static const unsigned sMinCapacity  = 1 << sMinCapacityLog2;
    static const unsigned sMaxInit      = JS_BIT(CAP_BITS - 1);
    static const unsigned sMaxCapacity  = JS_BIT(CAP_BITS);
    static const unsigned sHashBits     = mozilla::tl::BitSize<HashNumber>::value;

    // Hash-table alpha is conceptually a fraction, but to avoid floating-point
    // math we implement it as a ratio of integers.
    static const uint8_t sAlphaDenominator = 4;
    static const uint8_t sMinAlphaNumerator = 1; // min alpha: 1/4
    static const uint8_t sMaxAlphaNumerator = 3; // max alpha: 3/4

    static const HashNumber sFreeKey = Entry::sFreeKey;
    static const HashNumber sRemovedKey = Entry::sRemovedKey;
    static const HashNumber sCollisionBit = Entry::sCollisionBit;

    void setTableSizeLog2(unsigned sizeLog2)
    {
        hashShift = sHashBits - sizeLog2;
    }

    static bool isLiveHash(HashNumber hash)
    {
        return Entry::isLiveHash(hash);
    }

    static HashNumber prepareHash(const Lookup& l)
    {
        HashNumber keyHash = ScrambleHashCode(HashPolicy::hash(l));

        // Avoid reserved hash codes.
        if (!isLiveHash(keyHash))
            keyHash -= (sRemovedKey + 1);
        return keyHash & ~sCollisionBit;
    }

    static Entry *createTable(AllocPolicy &alloc, uint32_t capacity)
    {
        static_assert(sFreeKey == 0,
                      "newly-calloc'd tables have to be considered empty");
        static_assert(sMaxCapacity <= SIZE_MAX / sizeof(Entry),
                      "would overflow allocating max number of entries");
        return static_cast<Entry*>(alloc.calloc_(capacity * sizeof(Entry)));
    }

    static void destroyTable(AllocPolicy &alloc, Entry *oldTable, uint32_t capacity)
    {
        for (Entry *e = oldTable, *end = e + capacity; e < end; ++e)
            e->destroyIfLive();
        alloc.free_(oldTable);
    }

  public:
    explicit HashTable(AllocPolicy ap)
      : AllocPolicy(ap)
      , table(nullptr)
      , gen(0)
      , entryCount(0)
      , removedCount(0)
      , hashShift(sHashBits)
#ifdef DEBUG
      , mutationCount(0)
      , mEntered(false)
#endif
    {}

    MOZ_WARN_UNUSED_RESULT bool init(uint32_t length)
    {
        MOZ_ASSERT(!initialized());

        // Reject all lengths whose initial computed capacity would exceed
        // sMaxCapacity.  Round that maximum length down to the nearest power
        // of two for speedier code.
        if (length > sMaxInit) {
            this->reportAllocOverflow();
            return false;
        }

        static_assert((sMaxInit * sAlphaDenominator) / sAlphaDenominator == sMaxInit,
                      "multiplication in numerator below could overflow");
        static_assert(sMaxInit * sAlphaDenominator <= UINT32_MAX - sMaxAlphaNumerator,
                      "numerator calculation below could potentially overflow");

        // Compute the smallest capacity allowing |length| elements to be
        // inserted without rehashing: ceil(length / max-alpha).  (Ceiling
        // integral division: <http://stackoverflow.com/a/2745086>.)
        uint32_t newCapacity =
            (length * sAlphaDenominator + sMaxAlphaNumerator - 1) / sMaxAlphaNumerator;
        if (newCapacity < sMinCapacity)
            newCapacity = sMinCapacity;

        // FIXME: use JS_CEILING_LOG2 when PGO stops crashing (bug 543034).
        uint32_t roundUp = sMinCapacity, roundUpLog2 = sMinCapacityLog2;
        while (roundUp < newCapacity) {
            roundUp <<= 1;
            ++roundUpLog2;
        }

        newCapacity = roundUp;
        MOZ_ASSERT(newCapacity >= length);
        MOZ_ASSERT(newCapacity <= sMaxCapacity);

        table = createTable(*this, newCapacity);
        if (!table)
            return false;

        setTableSizeLog2(roundUpLog2);
        METER(memset(&stats, 0, sizeof(stats)));
        return true;
    }

    bool initialized() const
    {
        return !!table;
    }

    ~HashTable()
    {
        if (table)
            destroyTable(*this, table, capacity());
    }

  private:
    HashNumber hash1(HashNumber hash0) const
    {
        return hash0 >> hashShift;
    }

    struct DoubleHash
    {
        HashNumber h2;
        HashNumber sizeMask;
    };

    DoubleHash hash2(HashNumber curKeyHash) const
    {
        unsigned sizeLog2 = sHashBits - hashShift;
        DoubleHash dh = {
            ((curKeyHash << sizeLog2) >> hashShift) | 1,
            (HashNumber(1) << sizeLog2) - 1
        };
        return dh;
    }

    static HashNumber applyDoubleHash(HashNumber h1, const DoubleHash &dh)
    {
        return (h1 - dh.h2) & dh.sizeMask;
    }

    bool overloaded()
    {
        static_assert(sMaxCapacity <= UINT32_MAX / sMaxAlphaNumerator,
                      "multiplication below could overflow");
        return entryCount + removedCount >=
               capacity() * sMaxAlphaNumerator / sAlphaDenominator;
    }

    // Would the table be underloaded if it had the given capacity and entryCount?
    static bool wouldBeUnderloaded(uint32_t capacity, uint32_t entryCount)
    {
        static_assert(sMaxCapacity <= UINT32_MAX / sMinAlphaNumerator,
                      "multiplication below could overflow");
        return capacity > sMinCapacity &&
               entryCount <= capacity * sMinAlphaNumerator / sAlphaDenominator;
    }

    bool underloaded()
    {
        return wouldBeUnderloaded(capacity(), entryCount);
    }

    static bool match(Entry &e, const Lookup &l)
    {
        return HashPolicy::match(HashPolicy::getKey(e.get()), l);
    }

    Entry &lookup(const Lookup &l, HashNumber keyHash, unsigned collisionBit) const
    {
        MOZ_ASSERT(isLiveHash(keyHash));
        MOZ_ASSERT(!(keyHash & sCollisionBit));
        MOZ_ASSERT(collisionBit == 0 || collisionBit == sCollisionBit);
        MOZ_ASSERT(table);
        METER(stats.searches++);

        // Compute the primary hash address.
        HashNumber h1 = hash1(keyHash);
        Entry *entry = &table[h1];

        // Miss: return space for a new entry.
        if (entry->isFree()) {
            METER(stats.misses++);
            return *entry;
        }

        // Hit: return entry.
        if (entry->matchHash(keyHash) && match(*entry, l)) {
            METER(stats.hits++);
            return *entry;
        }

        // Collision: double hash.
        DoubleHash dh = hash2(keyHash);

        // Save the first removed entry pointer so we can recycle later.
        Entry *firstRemoved = nullptr;

        while(true) {
            if (MOZ_UNLIKELY(entry->isRemoved())) {
                if (!firstRemoved)
                    firstRemoved = entry;
            } else {
                entry->setCollision(collisionBit);
            }

            METER(stats.steps++);
            h1 = applyDoubleHash(h1, dh);

            entry = &table[h1];
            if (entry->isFree()) {
                METER(stats.misses++);
                return firstRemoved ? *firstRemoved : *entry;
            }

            if (entry->matchHash(keyHash) && match(*entry, l)) {
                METER(stats.hits++);
                return *entry;
            }
        }
    }

    // This is a copy of lookup hardcoded to the assumptions:
    //   1. the lookup is a lookupForAdd
    //   2. the key, whose |keyHash| has been passed is not in the table,
    //   3. no entries have been removed from the table.
    // This specialized search avoids the need for recovering lookup values
    // from entries, which allows more flexible Lookup/Key types.
    Entry &findFreeEntry(HashNumber keyHash)
    {
        MOZ_ASSERT(!(keyHash & sCollisionBit));
        MOZ_ASSERT(table);
        METER(stats.searches++);

        // We assume 'keyHash' has already been distributed.

        // Compute the primary hash address.
        HashNumber h1 = hash1(keyHash);
        Entry *entry = &table[h1];

        // Miss: return space for a new entry.
        if (!entry->isLive()) {
            METER(stats.misses++);
            return *entry;
        }

        // Collision: double hash.
        DoubleHash dh = hash2(keyHash);

        while(true) {
            MOZ_ASSERT(!entry->isRemoved());
            entry->setCollision();

            METER(stats.steps++);
            h1 = applyDoubleHash(h1, dh);

            entry = &table[h1];
            if (!entry->isLive()) {
                METER(stats.misses++);
                return *entry;
            }
        }
    }

    enum RebuildStatus { NotOverloaded, Rehashed, RehashFailed };

    RebuildStatus changeTableSize(int deltaLog2)
    {
        // Look, but don't touch, until we succeed in getting new entry store.
        Entry *oldTable = table;
        uint32_t oldCap = capacity();
        uint32_t newLog2 = sHashBits - hashShift + deltaLog2;
        uint32_t newCapacity = JS_BIT(newLog2);
        if (newCapacity > sMaxCapacity) {
            this->reportAllocOverflow();
            return RehashFailed;
        }

        Entry *newTable = createTable(*this, newCapacity);
        if (!newTable)
            return RehashFailed;

        // We can't fail from here on, so update table parameters.
        setTableSizeLog2(newLog2);
        removedCount = 0;
        gen++;
        table = newTable;

        // Copy only live entries, leaving removed ones behind.
        for (Entry *src = oldTable, *end = src + oldCap; src < end; ++src) {
            if (src->isLive()) {
                HashNumber hn = src->getKeyHash();
                findFreeEntry(hn).setLive(hn, mozilla::Move(src->get()));
                src->destroy();
            }
        }

        // All entries have been destroyed, no need to destroyTable.
        this->free_(oldTable);
        return Rehashed;
    }

    RebuildStatus checkOverloaded()
    {
        if (!overloaded())
            return NotOverloaded;

        // Compress if a quarter or more of all entries are removed.
        int deltaLog2;
        if (removedCount >= (capacity() >> 2)) {
            METER(stats.compresses++);
            deltaLog2 = 0;
        } else {
            METER(stats.grows++);
            deltaLog2 = 1;
        }

        return changeTableSize(deltaLog2);
    }

    // Infallibly rehash the table if we are overloaded with removals.
    void checkOverRemoved()
    {
        if (overloaded()) {
            if (checkOverloaded() == RehashFailed)
                rehashTableInPlace();
        }
    }

    void remove(Entry &e)
    {
        MOZ_ASSERT(table);
        METER(stats.removes++);

        if (e.hasCollision()) {
            e.removeLive();
            removedCount++;
        } else {
            METER(stats.removeFrees++);
            e.clearLive();
        }
        entryCount--;
#ifdef DEBUG
        mutationCount++;
#endif
    }

    void checkUnderloaded()
    {
        if (underloaded()) {
            METER(stats.shrinks++);
            (void) changeTableSize(-1);
        }
    }

    // Resize the table down to the largest capacity which doesn't underload the
    // table.  Since we call checkUnderloaded() on every remove, you only need
    // to call this after a bulk removal of items done without calling remove().
    void compactIfUnderloaded()
    {
        int32_t resizeLog2 = 0;
        uint32_t newCapacity = capacity();
        while (wouldBeUnderloaded(newCapacity, entryCount)) {
            newCapacity = newCapacity >> 1;
            resizeLog2--;
        }

        if (resizeLog2 != 0) {
            changeTableSize(resizeLog2);
        }
    }

    // This is identical to changeTableSize(currentSize), but without requiring
    // a second table.  We do this by recycling the collision bits to tell us if
    // the element is already inserted or still waiting to be inserted.  Since
    // already-inserted elements win any conflicts, we get the same table as we
    // would have gotten through random insertion order.
    void rehashTableInPlace()
    {
        METER(stats.rehashes++);
        removedCount = 0;
        for (size_t i = 0; i < capacity(); ++i)
            table[i].unsetCollision();

        for (size_t i = 0; i < capacity();) {
            Entry *src = &table[i];

            if (!src->isLive() || src->hasCollision()) {
                ++i;
                continue;
            }

            HashNumber keyHash = src->getKeyHash();
            HashNumber h1 = hash1(keyHash);
            DoubleHash dh = hash2(keyHash);
            Entry *tgt = &table[h1];
            while (true) {
                if (!tgt->hasCollision()) {
                    src->swap(tgt);
                    tgt->setCollision();
                    break;
                }

                h1 = applyDoubleHash(h1, dh);
                tgt = &table[h1];
            }
        }

        // TODO: this algorithm leaves collision bits on *all* elements, even if
        // they are on no collision path. We have the option of setting the
        // collision bits correctly on a subsequent pass or skipping the rehash
        // unless we are totally filled with tombstones: benchmark to find out
        // which approach is best.
    }

  public:
    void clear()
    {
        if (mozilla::IsPod<Entry>::value) {
            memset(table, 0, sizeof(*table) * capacity());
        } else {
            uint32_t tableCapacity = capacity();
            for (Entry *e = table, *end = table + tableCapacity; e < end; ++e)
                e->clear();
        }
        removedCount = 0;
        entryCount = 0;
#ifdef DEBUG
        mutationCount++;
#endif
    }

    void finish()
    {
        MOZ_ASSERT(!mEntered);

        if (!table)
            return;

        destroyTable(*this, table, capacity());
        table = nullptr;
        gen++;
        entryCount = 0;
        removedCount = 0;
#ifdef DEBUG
        mutationCount++;
#endif
    }

    Range all() const
    {
        MOZ_ASSERT(table);
        return Range(*this, table, table + capacity());
    }

    bool empty() const
    {
        MOZ_ASSERT(table);
        return !entryCount;
    }

    uint32_t count() const
    {
        MOZ_ASSERT(table);
        return entryCount;
    }

    uint32_t capacity() const
    {
        MOZ_ASSERT(table);
        return JS_BIT(sHashBits - hashShift);
    }

    uint32_t generation() const
    {
        MOZ_ASSERT(table);
        return gen;
    }

    size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const
    {
        return mallocSizeOf(table);
    }

    size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const
    {
        return mallocSizeOf(this) + sizeOfExcludingThis(mallocSizeOf);
    }

    Ptr lookup(const Lookup &l) const
    {
        mozilla::ReentrancyGuard g(*this);
        HashNumber keyHash = prepareHash(l);
        return Ptr(lookup(l, keyHash, 0), *this);
    }

    Ptr readonlyThreadsafeLookup(const Lookup &l) const
    {
        HashNumber keyHash = prepareHash(l);
        return Ptr(lookup(l, keyHash, 0), *this);
    }

    AddPtr lookupForAdd(const Lookup &l) const
    {
        mozilla::ReentrancyGuard g(*this);
        HashNumber keyHash = prepareHash(l);
        Entry &entry = lookup(l, keyHash, sCollisionBit);
        AddPtr p(entry, *this, keyHash);
        return p;
    }

    template <class U>
    bool add(AddPtr &p, U &&u)
    {
        mozilla::ReentrancyGuard g(*this);
        MOZ_ASSERT(table);
        MOZ_ASSERT(!p.found());
        MOZ_ASSERT(!(p.keyHash & sCollisionBit));

        // Changing an entry from removed to live does not affect whether we
        // are overloaded and can be handled separately.
        if (p.entry_->isRemoved()) {
            METER(stats.addOverRemoved++);
            removedCount--;
            p.keyHash |= sCollisionBit;
        } else {
            // Preserve the validity of |p.entry_|.
            RebuildStatus status = checkOverloaded();
            if (status == RehashFailed)
                return false;
            if (status == Rehashed)
                p.entry_ = &findFreeEntry(p.keyHash);
        }

        p.entry_->setLive(p.keyHash, mozilla::Forward<U>(u));
        entryCount++;
#ifdef DEBUG
        mutationCount++;
        p.generation = generation();
        p.mutationCount = mutationCount;
#endif
        return true;
    }

    // Note: |l| may be a reference to a piece of |u|, so this function
    // must take care not to use |l| after moving |u|.
    template <class U>
    void putNewInfallible(const Lookup &l, U &&u)
    {
        MOZ_ASSERT(table);

        HashNumber keyHash = prepareHash(l);
        Entry *entry = &findFreeEntry(keyHash);

        if (entry->isRemoved()) {
            METER(stats.addOverRemoved++);
            removedCount--;
            keyHash |= sCollisionBit;
        }

        entry->setLive(keyHash, mozilla::Forward<U>(u));
        entryCount++;
#ifdef DEBUG
        mutationCount++;
#endif
    }

    // Note: |l| may be a reference to a piece of |u|, so this function
    // must take care not to use |l| after moving |u|.
    template <class U>
    bool putNew(const Lookup &l, U &&u)
    {
        if (checkOverloaded() == RehashFailed)
            return false;

        putNewInfallible(l, mozilla::Forward<U>(u));
        return true;
    }

    // Note: |l| may be a reference to a piece of |u|, so this function
    // must take care not to use |l| after moving |u|.
    template <class U>
    bool relookupOrAdd(AddPtr& p, const Lookup &l, U &&u)
    {
#ifdef DEBUG
        p.generation = generation();
        p.mutationCount = mutationCount;
#endif
        {
            mozilla::ReentrancyGuard g(*this);
            MOZ_ASSERT(prepareHash(l) == p.keyHash); // l has not been destroyed
            p.entry_ = &lookup(l, p.keyHash, sCollisionBit);
        }
        return p.found() || add(p, mozilla::Forward<U>(u));
    }

    void remove(Ptr p)
    {
        MOZ_ASSERT(table);
        mozilla::ReentrancyGuard g(*this);
        MOZ_ASSERT(p.found());
        remove(*p.entry_);
        checkUnderloaded();
    }

    void rekeyWithoutRehash(Ptr p, const Lookup &l, const Key &k)
    {
        MOZ_ASSERT(table);
        mozilla::ReentrancyGuard g(*this);
        MOZ_ASSERT(p.found());
        typename HashTableEntry<T>::NonConstT t(mozilla::Move(*p));
        HashPolicy::setKey(t, const_cast<Key &>(k));
        remove(*p.entry_);
        putNewInfallible(l, mozilla::Move(t));
    }

    void rekeyAndMaybeRehash(Ptr p, const Lookup &l, const Key &k)
    {
        rekeyWithoutRehash(p, l, k);
        checkOverRemoved();
    }

    void rekeyInPlace(Ptr p, const Key &k)
    {
        MOZ_ASSERT(table);
        mozilla::ReentrancyGuard g(*this);
        MOZ_ASSERT(p.found());
        HashPolicy::rekey(const_cast<Key &>(*p), const_cast<Key &>(k));
    }

#undef METER
};

}  // namespace detail
}  // namespace js

#endif  /* js_HashTable_h */