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//
// Compile-time string hashing function.
//
// Example of usage:
// printf( "Hash test: %u", StringHash("test").GetHash() );
// printf( "Hash test: %u", StringHash("aVeryLongTestWhichStillWorks").GetHash() );
//
#ifndef STRING_HASH_H
#define STRING_HASH_H
// Try and use an inline that will force it to happen.
// icc -inline-level=1 -inline-forceinline, and with Apple's gcc you can use gcc -obey-inline.
#if defined(_MSC_VER)
// MSVC is __forceinline.
#define FORCE_INLINE __forceinline
#elif defined(__GNUC__)
// gcc is an attribute.
#define FORCE_INLINE __attribute__((always_inline))
#else
// default to inline.
#define FORCE_INLINE inline
#endif
// Hashing function. If the FNV is not working well, we can try Murmur Hash or City Hash
template <unsigned int N, unsigned int I>
struct FnvHash
{
FORCE_INLINE static unsigned int Hash(const char (&str)[N])
{
return( (FnvHash<N, I-1>::Hash(str) ^ str[I-1]) * 16777619u );
}
};
template <unsigned int N>
struct FnvHash<N, 1>
{
FORCE_INLINE static unsigned int Hash(const char (&str)[N])
{
return( (2166136261u ^ str[0]) * 16777619u );
}
};
class StringHash
{
public:
template <unsigned int N>
FORCE_INLINE StringHash(const char (&str)[N])
: m_hash(FnvHash<N, N>::Hash(str))
{
}
FORCE_INLINE unsigned int GetHash() { return( m_hash ); }
private:
unsigned int m_hash;
};
#endif // STRING_HASH_H
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