1/*
2 * Copyright (C) 2006, 2007, 2008, 2012, 2013 Apple Inc. All rights reserved
3 * Copyright (C) Research In Motion Limited 2009. All rights reserved.
4 *
5 * This library is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU Library General Public
7 * License as published by the Free Software Foundation; either
8 * version 2 of the License, or (at your option) any later version.
9 *
10 * This library is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13 * Library General Public License for more details.
14 *
15 * You should have received a copy of the GNU Library General Public License
16 * along with this library; see the file COPYING.LIB.  If not, write to
17 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
18 * Boston, MA 02110-1301, USA.
19 *
20 */
21
22#ifndef StringHash_h
23#define StringHash_h
24
25#include "wtf/text/AtomicString.h"
26#include "wtf/HashTraits.h"
27#include "wtf/StringHasher.h"
28
29namespace WTF {
30
31    inline bool HashTraits<String>::isEmptyValue(const String& value)
32    {
33        return value.isNull();
34    }
35
36    // The hash() functions on StringHash and CaseFoldingHash do not support
37    // null strings. get(), contains(), and add() on HashMap<String,..., StringHash>
38    // cause a null-pointer dereference when passed null strings.
39
40    // FIXME: We should really figure out a way to put the computeHash function that's
41    // currently a member function of StringImpl into this file so we can be a little
42    // closer to having all the nearly-identical hash functions in one place.
43
44    struct StringHash {
45        static unsigned hash(StringImpl* key) { return key->hash(); }
46        static inline bool equal(const StringImpl* a, const StringImpl* b)
47        {
48            return equalNonNull(a, b);
49        }
50
51        static unsigned hash(const RefPtr<StringImpl>& key) { return key->hash(); }
52        static bool equal(const RefPtr<StringImpl>& a, const RefPtr<StringImpl>& b)
53        {
54            return equal(a.get(), b.get());
55        }
56
57        static unsigned hash(const String& key) { return key.impl()->hash(); }
58        static bool equal(const String& a, const String& b)
59        {
60            return equal(a.impl(), b.impl());
61        }
62
63        static const bool safeToCompareToEmptyOrDeleted = false;
64    };
65
66    class CaseFoldingHash {
67    public:
68        template<typename T> static inline UChar foldCase(T ch)
69        {
70            return WTF::Unicode::foldCase(ch);
71        }
72
73        static unsigned hash(const UChar* data, unsigned length)
74        {
75            return StringHasher::computeHashAndMaskTop8Bits<UChar, foldCase<UChar> >(data, length);
76        }
77
78        static unsigned hash(StringImpl* str)
79        {
80            if (str->is8Bit())
81                return hash(str->characters8(), str->length());
82            return hash(str->characters16(), str->length());
83        }
84
85        static unsigned hash(const LChar* data, unsigned length)
86        {
87            return StringHasher::computeHashAndMaskTop8Bits<LChar, foldCase<LChar> >(data, length);
88        }
89
90        static inline unsigned hash(const char* data, unsigned length)
91        {
92            return CaseFoldingHash::hash(reinterpret_cast<const LChar*>(data), length);
93        }
94
95        static inline bool equal(const StringImpl* a, const StringImpl* b)
96        {
97            return equalIgnoringCaseNonNull(a, b);
98        }
99
100        static unsigned hash(const RefPtr<StringImpl>& key)
101        {
102            return hash(key.get());
103        }
104
105        static bool equal(const RefPtr<StringImpl>& a, const RefPtr<StringImpl>& b)
106        {
107            return equal(a.get(), b.get());
108        }
109
110        static unsigned hash(const String& key)
111        {
112            return hash(key.impl());
113        }
114        static unsigned hash(const AtomicString& key)
115        {
116            return hash(key.impl());
117        }
118        static bool equal(const String& a, const String& b)
119        {
120            return equal(a.impl(), b.impl());
121        }
122        static bool equal(const AtomicString& a, const AtomicString& b)
123        {
124            return (a == b) || equal(a.impl(), b.impl());
125        }
126
127        static const bool safeToCompareToEmptyOrDeleted = false;
128    };
129
130    // This hash can be used in cases where the key is a hash of a string, but we don't
131    // want to store the string. It's not really specific to string hashing, but all our
132    // current uses of it are for strings.
133    struct AlreadyHashed : IntHash<unsigned> {
134        static unsigned hash(unsigned key) { return key; }
135
136        // To use a hash value as a key for a hash table, we need to eliminate the
137        // "deleted" value, which is negative one. That could be done by changing
138        // the string hash function to never generate negative one, but this works
139        // and is still relatively efficient.
140        static unsigned avoidDeletedValue(unsigned hash)
141        {
142            ASSERT(hash);
143            unsigned newHash = hash | (!(hash + 1) << 31);
144            ASSERT(newHash);
145            ASSERT(newHash != 0xFFFFFFFF);
146            return newHash;
147        }
148    };
149
150}
151
152using WTF::AlreadyHashed;
153using WTF::CaseFoldingHash;
154using WTF::StringHash;
155
156#endif
157