third_party/WebKit/Source/wtf/text/AtomicStringHash.h

   1 /*
   2  * Copyright (C) 2008 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  *
   8  * 1.  Redistributions of source code must retain the above copyright
   9  *     notice, this list of conditions and the following disclaimer.
  10  * 2.  Redistributions in binary form must reproduce the above copyright
  11  *     notice, this list of conditions and the following disclaimer in the
  12  *     documentation and/or other materials provided with the distribution.
  13  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
  14  *     its contributors may be used to endorse or promote products derived
  15  *     from this software without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
  18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  20  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
  21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  24  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 #ifndef AtomicStringHash_h
  30 #define AtomicStringHash_h
  31
  32 #include "wtf/text/AtomicString.h"
  33 #include "wtf/HashTraits.h"
  34
  35 namespace WTF {
  36
  37     struct AtomicStringHash {
  38         static unsigned hash(const AtomicString& key)
  39         {
  40             return key.impl()->existingHash();
  41         }
  42
  43         static bool equal(const AtomicString& a, const AtomicString& b)
  44         {
  45             return a == b;
  46         }
  47
  48         static const bool safeToCompareToEmptyOrDeleted = false;
  49     };
  50
  51     // AtomicStringHash is the default hash for AtomicString
  52     template<> struct HashTraits<AtomicString> : SimpleClassHashTraits<AtomicString> {
  53         // Unlike other types, we can return a const reference for AtomicString's empty value (nullAtom).
  54         typedef const AtomicString& PeekOutType;
  55
  56         static const AtomicString& emptyValue() { return nullAtom; }
  57         static PeekOutType peek(const AtomicString& value) { return value; }
  58
  59         static const bool hasIsEmptyValueFunction = true;
  60         static bool isEmptyValue(const AtomicString& value) { return value.isNull(); }
  61     };
  62
  63 }
  64
  65 using WTF::AtomicStringHash;
  66
  67 #endif