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public/tier1/generichash.h

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+//======= Copyright <20> 2005, , Valve Corporation, All rights reserved. =========
+//
+// Purpose: Variant Pearson Hash general purpose hashing algorithm described
+//			by Cargill in C++ Report 1994. Generates a 16-bit result.
+//
+//=============================================================================
+
+#ifndef GENERICHASH_H
+#define GENERICHASH_H
+
+#if defined(_WIN32)
+#pragma once
+#endif
+
+//-----------------------------------------------------------------------------
+
+unsigned FASTCALL HashString( const char *pszKey );
+unsigned FASTCALL HashStringCaseless( const char *pszKey );
+unsigned FASTCALL HashStringCaselessConventional( const char *pszKey );
+unsigned FASTCALL Hash4( const void *pKey );
+unsigned FASTCALL Hash8( const void *pKey );
+unsigned FASTCALL Hash12( const void *pKey );
+unsigned FASTCALL Hash16( const void *pKey );
+unsigned FASTCALL HashBlock( const void *pKey, unsigned size );
+
+unsigned FASTCALL HashInt( const int key );
+
+// hash a uint32 into a uint32
+FORCEINLINE uint32 HashIntAlternate( uint32 n)
+{
+	n = ( n + 0x7ed55d16 ) + ( n << 12 );
+	n = ( n ^ 0xc761c23c ) ^ ( n >> 19 );
+	n = ( n + 0x165667b1 ) + ( n << 5 );
+	n = ( n + 0xd3a2646c ) ^ ( n << 9 );
+	n = ( n + 0xfd7046c5 ) + ( n << 3 );
+	n = ( n ^ 0xb55a4f09 ) ^ ( n >> 16 );
+	return n;
+}
+
+
+inline uint64 HashUint64( uint64 s )
+{
+	// Thomas Wang hash, http://www.concentric.net/~ttwang/tech/inthash.htm
+	s = ( ~s ) + ( s << 21 ); // s = (s << 21) - s - 1;
+	s = s ^ ( s >> 24 );
+	s = ( s + ( s << 3 ) ) + ( s << 8 ); // s * 265
+	s = s ^ ( s >> 14 );
+	s = ( s + ( s << 2 ) ) + ( s << 4 ); // s * 21
+	s = s ^ ( s >> 28 );
+	s = s + ( s << 31 );
+	return s;
+}
+
+
+inline intp HashIntp( intp s )
+{
+#ifdef PLATFORM_64BITS
+	COMPILE_TIME_ASSERT( sizeof( s ) == sizeof( uint64 ) );
+	return ( intp )HashUint64( ( uint64 )s );
+#else
+	return HashInt( s );
+#endif
+}
+
+inline unsigned HashIntConventional( const int n ) // faster but less effective
+{
+	// first byte
+	unsigned hash = 0xAAAAAAAA + (n & 0xFF);
+	// second byte
+	hash = ( hash << 5 ) + hash + ( (n >> 8) & 0xFF );
+	// third byte
+	hash = ( hash << 5 ) + hash + ( (n >> 16) & 0xFF );
+	// fourth byte
+	hash = ( hash << 5 ) + hash + ( (n >> 24) & 0xFF );
+
+	return hash;
+
+	/* this is the old version, which would cause a load-hit-store on every
+	   line on a PowerPC, and therefore took hundreds of clocks to execute!
+	  
+	byte *p = (byte *)&n;
+	unsigned hash = 0xAAAAAAAA + *p++;
+	hash = ( ( hash << 5 ) + hash ) + *p++;
+	hash = ( ( hash << 5 ) + hash ) + *p++;
+	return ( ( hash << 5 ) + hash ) + *p;
+	*/
+}
+
+//-----------------------------------------------------------------------------
+
+template <typename T>
+inline unsigned HashItem( const T &item )
+{
+	// TODO: Confirm comiler optimizes out unused paths
+	if ( sizeof(item) == 4 )
+		return Hash4( &item );
+	else if ( sizeof(item) == 8 )
+		return Hash8( &item );
+	else if ( sizeof(item) == 12 )
+		return Hash12( &item );
+	else if ( sizeof(item) == 16 )
+		return Hash16( &item );
+	else
+		return HashBlock( &item, sizeof(item) );
+}
+
+template <> inline unsigned HashItem<int>(const int &key )
+{
+	return HashInt( key );
+}
+
+template <> inline unsigned HashItem<unsigned>(const unsigned &key )
+{
+	return HashInt( (int)key );
+}
+
+template<> inline unsigned HashItem<const char *>(const char * const &pszKey )
+{
+	return HashString( pszKey );
+}
+
+template<> inline unsigned HashItem<char *>(char * const &pszKey )
+{
+	return HashString( pszKey );
+}
+
+//-----------------------------------------------------------------------------
+
+
+//-----------------------------------------------------------------------------
+// Murmur hash
+//-----------------------------------------------------------------------------
+uint32 MurmurHash2( const void * key, int len, uint32 seed );
+
+// return murmurhash2 of a downcased string
+uint32 MurmurHash2LowerCase( char const *pString, uint32 nSeed );
+
+uint64 MurmurHash64( const void * key, int len, uint32 seed );
+
+
+#endif /* !GENERICHASH_H */