/*
* 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 "PlatformString.h"
#include <wtf/HashTraits.h>
#include <wtf/StringHashFunctions.h>
#include <wtf/unicode/Unicode.h>
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(StringImpl* a, 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(StringImpl* a, 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