--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/JavaScriptCore/wtf/text/StringHash.h Fri Sep 17 09:02:29 2010 +0300
@@ -0,0 +1,268 @@
+/*
+ * 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