_ak_f_n_v_hash_8h

Other Documentation

Wwise SDK 2022.1.4

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 #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.

 //

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

 //

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

 #include <AK/SoundEngine/Common/AkNumeralTypes.h>

 namespace AK

 {

     struct Hash32

     {

         typedef AkUInt32 HashType;

         typedef AkUInt32 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 AkUInt64 HashType;

         typedef AkUInt64 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)); }

         static inline typename HashParams::HashType ComputeLowerCase(const char* in_pData);

     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);

     }

     template <class HashParams>

     typename HashParams::HashType FNVHash<HashParams>::ComputeLowerCase(const char* in_pData)

     {       

         typename HashParams::HashType hval = HashParams::s_offsetBasis;

         //Convert to lowercase and hash the string in one loop

         while (*in_pData != 0)

         {

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

             unsigned char c = (unsigned char)*in_pData++;

             c = (c >= 'A' && c <= 'Z') ? c - 'A' + 'a' : c;

             hval ^= c; // xor the bottom with the current octet

         }

         // 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