gecko-dev/xpcom/ds/nsPointerHashKeys.h
Ehsan Akhgari 43091e2839 Bug 1379282 - Improve XPCOM's pointer hashing functions for pointers to neighboring memory locations; r=erahm
The simplistic shift-based hashing function creates a lot of collisions
for pointers pointing to arrays as it doesn't do a great job at distributing
the data randomly based on the input bytes.
2017-07-19 14:16:35 -04:00

50 lines
1.3 KiB
C++

/* -*- 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/. */
/* Definitions for nsPtrHashKey<T> and nsVoidPtrHashKey. */
#ifndef nsPointerHashKeys_h
#define nsPointerHashKeys_h
#include "nscore.h"
#include "mozilla/Attributes.h"
#include "mozilla/HashFunctions.h"
/**
* hashkey wrapper using T* KeyType
*
* @see nsTHashtable::EntryType for specification
*/
template<class T>
class nsPtrHashKey : public PLDHashEntryHdr
{
public:
typedef T* KeyType;
typedef const T* KeyTypePointer;
explicit nsPtrHashKey(const T* aKey) : mKey(const_cast<T*>(aKey)) {}
nsPtrHashKey(const nsPtrHashKey<T>& aToCopy) : mKey(aToCopy.mKey) {}
~nsPtrHashKey() {}
KeyType GetKey() const { return mKey; }
bool KeyEquals(KeyTypePointer aKey) const { return aKey == mKey; }
static KeyTypePointer KeyToPointer(KeyType aKey) { return aKey; }
static PLDHashNumber HashKey(KeyTypePointer aKey)
{
return mozilla::HashGeneric(aKey);
}
enum { ALLOW_MEMMOVE = true };
protected:
T* MOZ_NON_OWNING_REF mKey;
};
typedef nsPtrHashKey<const void> nsVoidPtrHashKey;
#endif // nsPointerHashKeys_h