_ak_f_n_v_hash_8h

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Wwise SDK 2019.2.15

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 /*******************************************************************************

 The content of this file includes portions of the AUDIOKINETIC Wwise Technology

 released in source code form as part of the SDK installer package.

 Commercial License Usage

 Licensees holding valid commercial licenses to the AUDIOKINETIC Wwise Technology

 may use this file in accordance with the end user license agreement provided 

 with the software or, alternatively, in accordance with the terms contained in a

 written agreement between you and Audiokinetic Inc.

 Apache License Usage

 Alternatively, this file may be used under the Apache License, Version 2.0 (the 

 "Apache License"); you may not use this file except in compliance with the 

 Apache License. You may obtain a copy of the Apache License at 

 http://www.apache.org/licenses/LICENSE-2.0.

 Unless required by applicable law or agreed to in writing, software distributed

 under the Apache License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES

 OR CONDITIONS OF ANY KIND, either express or implied. See the Apache License for

 the specific language governing permissions and limitations under the License.

   Version: <VERSION>  Build: <BUILDNUMBER>

   Copyright (c) <COPYRIGHTYEAR> Audiokinetic Inc.

 *******************************************************************************/

 #ifndef _FNVHASH_H

 #define _FNVHASH_H

 // http://www.isthe.com/chongo/tech/comp/fnv/

 //////////////////////////////////////////////////////////////////

 //

 // ***************************************************************

 //

 // IMPORTANT: The Migration Utility contains a C# version of this

 // class, to assign Short IDs to objects created during migration.

 // If you modify this class, be sure to update its C# counterpart,

 // ShortIDGenerator, at the same time.

 //

 // ***************************************************************

 //

 //////////////////////////////////////////////////////////////////

 namespace AK

 {

     struct Hash32

     {

         typedef unsigned int HashType;

         typedef unsigned int SizeType;

         static inline unsigned int Bits() {return 32;}

         static inline HashType Prime() {return 16777619;}

         static const HashType s_offsetBasis = 2166136261U;

     };

     struct Hash30 : public Hash32

     {

         static inline unsigned int Bits() {return 30;}

     };

     struct Hash64

     {

         typedef unsigned long long HashType;

         typedef unsigned long long SizeType;

         static inline unsigned int Bits() {return 64;}

         static inline HashType Prime() {return 1099511628211ULL;}

         static const HashType s_offsetBasis = 14695981039346656037ULL;

     };

     template <class HashParams> 

     class FNVHash

     {

     public:

         inline FNVHash( typename HashParams::HashType in_uBase = HashParams::s_offsetBasis );   ///< Constructor

         /// Turn the provided data into a hash value.

         /// When Wwise uses this hash with strings, it always provides lower case strings only.

         /// Call this repeatedly on the same instance to build a hash incrementally.

         inline typename HashParams::HashType Compute( const void* in_pData, typename HashParams::SizeType in_dataSize );

         inline typename HashParams::HashType Get() const { return m_uHash; }

         template <typename T>

         inline typename HashParams::HashType Compute(const T& in_pData) { return Compute(&in_pData, sizeof(T)); }

     private:

         typename HashParams::HashType m_uHash;

     };

     #if defined(_MSC_VER)

     #pragma warning(push)

     #pragma warning(disable:4127)

     #endif

     template <class HashParams> 

     FNVHash<HashParams>::FNVHash( typename HashParams::HashType in_uBase )

         : m_uHash( in_uBase )

     {

     }

     template <class HashParams> 

     typename HashParams::HashType FNVHash<HashParams>::Compute( const void* in_pData, typename HashParams::SizeType in_dataSize )

     {

         const unsigned char* pData = (const unsigned char*) in_pData;

         const unsigned char* pEnd = pData + in_dataSize;        /* beyond end of buffer */

         typename HashParams::HashType hval = m_uHash;

         // FNV-1 hash each octet in the buffer

         while( pData < pEnd ) 

         {

             hval *= HashParams::Prime(); // multiply by the 32 bit FNV magic prime mod 2^32

             hval ^= *pData++; // xor the bottom with the current octet

         }

         m_uHash = hval;

         // XOR-Fold to the required number of bits

         if( HashParams::Bits() >= sizeof(typename HashParams::HashType) * 8 )

             return hval;

         typename HashParams::HashType mask = static_cast<typename HashParams::HashType>(((typename HashParams::HashType)1 << HashParams::Bits())-1);

         return (typename HashParams::HashType)(hval >> HashParams::Bits()) ^ (hval & mask);

     }

     #if defined(_MSC_VER)

     #pragma warning(pop)

     #endif

     typedef FNVHash<Hash32> FNVHash32;

     typedef FNVHash<Hash30> FNVHash30;

     typedef FNVHash<Hash64> FNVHash64;

 }

 #endif