FCL/sf/mw/qtwebkit: comparison JavaScriptCore/wtf/text/StringHash.h

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+/*
+* Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved
+* Copyright (C) Research In Motion Limited 2009. All rights reserved.
+*
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU Library General Public
+* License as published by the Free Software Foundation; either
+* version 2 of the License, or (at your option) any later version.
+*
+* This library is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+* Library General Public License for more details.
+*
+* You should have received a copy of the GNU Library General Public License
+* along with this library; see the file COPYING.LIB.  If not, write to
+* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+* Boston, MA 02110-1301, USA.
+*
+*/
+#ifndef StringHash_h
+#define StringHash_h
+#include "AtomicString.h"
+#include "WTFString.h"
+#include <wtf/HashTraits.h>
+#include <wtf/StringHashFunctions.h>
+#include <wtf/unicode/Unicode.h>
+// FIXME: This is a temporary layering violation while we move string code to WTF.
+// Landing the file moves in one patch, will follow on with patches to change the namespaces.
+namespace WebCore {
+// The hash() functions on StringHash and CaseFoldingHash do not support
+// null strings. get(), contains(), and add() on HashMap<String,..., StringHash>
+// cause a null-pointer dereference when passed null strings.
+// FIXME: We should really figure out a way to put the computeHash function that's
+// currently a member function of StringImpl into this file so we can be a little
+// closer to having all the nearly-identical hash functions in one place.
+struct StringHash {
+static unsigned hash(StringImpl* key) { return key->hash(); }
+static bool equal(const StringImpl* a, const StringImpl* b)
+{
+if (a == b)
+return true;
+if (!a || !b)
+return false;
+unsigned aLength = a->length();
+unsigned bLength = b->length();
+if (aLength != bLength)
+return false;
+// FIXME: perhaps we should have a more abstract macro that indicates when
+// going 4 bytes at a time is unsafe
+#if CPU(ARM) || CPU(SH4)
+const UChar* aChars = a->characters();
+const UChar* bChars = b->characters();
+for (unsigned i = 0; i != aLength; ++i) {
+if (*aChars++ != *bChars++)
+return false;
+}
+return true;
+#else
+/* Do it 4-bytes-at-a-time on architectures where it's safe */
+const uint32_t* aChars = reinterpret_cast<const uint32_t*>(a->characters());
+const uint32_t* bChars = reinterpret_cast<const uint32_t*>(b->characters());
+unsigned halfLength = aLength >> 1;
+for (unsigned i = 0; i != halfLength; ++i)
+if (*aChars++ != *bChars++)
+return false;
+if (aLength & 1 && *reinterpret_cast<const uint16_t*>(aChars) != *reinterpret_cast<const uint16_t*>(bChars))
+return false;
+return true;
+#endif
+}
+static unsigned hash(const RefPtr<StringImpl>& key) { return key->hash(); }
+static bool equal(const RefPtr<StringImpl>& a, const RefPtr<StringImpl>& b)
+{
+return equal(a.get(), b.get());
+}
+static unsigned hash(const String& key) { return key.impl()->hash(); }
+static bool equal(const String& a, const String& b)
+{
+return equal(a.impl(), b.impl());
+}
+static const bool safeToCompareToEmptyOrDeleted = false;
+};
+class CaseFoldingHash {
+public:
+// Paul Hsieh's SuperFastHash
+// http://www.azillionmonkeys.com/qed/hash.html
+static unsigned hash(const UChar* data, unsigned length)
+{
+unsigned l = length;
+const UChar* s = data;
+uint32_t hash = WTF::stringHashingStartValue;
+uint32_t tmp;
+int rem = l & 1;
+l >>= 1;
+// Main loop.
+for (; l > 0; l--) {
+hash += WTF::Unicode::foldCase(s[0]);
+tmp = (WTF::Unicode::foldCase(s[1]) << 11) ^ hash;
+hash = (hash << 16) ^ tmp;
+s += 2;
+hash += hash >> 11;
+}
+// Handle end case.
+if (rem) {
+hash += WTF::Unicode::foldCase(s[0]);
+hash ^= hash << 11;
+hash += hash >> 17;
+}
+// Force "avalanching" of final 127 bits.
+hash ^= hash << 3;
+hash += hash >> 5;
+hash ^= hash << 2;
+hash += hash >> 15;
+hash ^= hash << 10;
+// This avoids ever returning a hash code of 0, since that is used to
+// signal "hash not computed yet", using a value that is likely to be
+// effectively the same as 0 when the low bits are masked.
+hash |= !hash << 31;
+return hash;
+}
+static unsigned hash(StringImpl* str)
+{
+return hash(str->characters(), str->length());
+}
+static unsigned hash(const char* str, unsigned length)
+{
+// This hash is designed to work on 16-bit chunks at a time. But since the normal case
+// (above) is to hash UTF-16 characters, we just treat the 8-bit chars as if they
+// were 16-bit chunks, which will give matching results.
+unsigned l = length;
+const char* s = str;
+uint32_t hash = WTF::stringHashingStartValue;
+uint32_t tmp;
+int rem = l & 1;
+l >>= 1;
+// Main loop
+for (; l > 0; l--) {
+hash += WTF::Unicode::foldCase(s[0]);
+tmp = (WTF::Unicode::foldCase(s[1]) << 11) ^ hash;
+hash = (hash << 16) ^ tmp;
+s += 2;
+hash += hash >> 11;
+}
+// Handle end case
+if (rem) {
+hash += WTF::Unicode::foldCase(s[0]);
+hash ^= hash << 11;
+hash += hash >> 17;
+}
+// Force "avalanching" of final 127 bits
+hash ^= hash << 3;
+hash += hash >> 5;
+hash ^= hash << 2;
+hash += hash >> 15;
+hash ^= hash << 10;
+// this avoids ever returning a hash code of 0, since that is used to
+// signal "hash not computed yet", using a value that is likely to be
+// effectively the same as 0 when the low bits are masked
+hash |= !hash << 31;
+return hash;
+}
+static bool equal(const StringImpl* a, const StringImpl* b)
+{
+if (a == b)
+return true;
+if (!a || !b)
+return false;
+unsigned length = a->length();
+if (length != b->length())
+return false;
+return WTF::Unicode::umemcasecmp(a->characters(), b->characters(), length) == 0;
+}
+static unsigned hash(const RefPtr<StringImpl>& key)
+{
+return hash(key.get());
+}
+static bool equal(const RefPtr<StringImpl>& a, const RefPtr<StringImpl>& b)
+{
+return equal(a.get(), b.get());
+}
+static unsigned hash(const String& key)
+{
+return hash(key.impl());
+}
+static unsigned hash(const AtomicString& key)
+{
+return hash(key.impl());
+}
+static bool equal(const String& a, const String& b)
+{
+return equal(a.impl(), b.impl());
+}
+static bool equal(const AtomicString& a, const AtomicString& b)
+{
+return (a == b) || equal(a.impl(), b.impl());
+}
+static const bool safeToCompareToEmptyOrDeleted = false;
+};
+// This hash can be used in cases where the key is a hash of a string, but we don't
+// want to store the string. It's not really specific to string hashing, but all our
+// current uses of it are for strings.
+struct AlreadyHashed : IntHash<unsigned> {
+static unsigned hash(unsigned key) { return key; }
+// To use a hash value as a key for a hash table, we need to eliminate the
+// "deleted" value, which is negative one. That could be done by changing
+// the string hash function to never generate negative one, but this works
+// and is still relatively efficient.
+static unsigned avoidDeletedValue(unsigned hash)
+{
+ASSERT(hash);
+unsigned newHash = hash | (!(hash + 1) << 31);
+ASSERT(newHash);
+ASSERT(newHash != 0xFFFFFFFF);
+return newHash;
+}
+};
+}
+namespace WTF {
+template<> struct HashTraits<WebCore::String> : GenericHashTraits<WebCore::String> {
+static const bool emptyValueIsZero = true;
+static void constructDeletedValue(WebCore::String& slot) { new (&slot) WebCore::String(HashTableDeletedValue); }
+static bool isDeletedValue(const WebCore::String& slot) { return slot.isHashTableDeletedValue(); }
+};
+}
+#endif