_ak_f_n_v_hash_8h

Wwise SDK 2024.1.4

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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