WebCore/platform/text/StringHash.h - platform/external/webkit - Git at Google

 /*
  * 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
	/*
	* 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