Gaudi::Utils::QuasiRandom Namespace Reference

Functions
uint32_t	mix (uint32_t state)
	Create a hash with a large avalanche effect from a 32 bit integer. More...
uint32_t	mix32 (uint32_t state, uint32_t extra)
	mix some 'extra' entropy into 'state' and return result More...
uint32_t	mix64 (uint32_t state, uint64_t extra)
	mix some 'extra' entropy into 'state' and return result More...
uint32_t	mixString (uint32_t state, const std::string &extra)
	mix some 'extra' entropy into 'state' and return result More...

Function Documentation

uint32_t Gaudi::Utils::QuasiRandom::mix

(

uint32_t

state

)

Create a hash with a large avalanche effect from a 32 bit integer.

Definition at line 11 of file QuasiRandom.cpp.

{
   state += (state << 16); state ^= (state >> 13);
   state += (state <<  4); state ^= (state >>  7);
   state += (state << 10); state ^= (state >>  5);
   state += (state <<  8); state ^= (state >> 16);
   return state;
}

uint32_t Gaudi::Utils::QuasiRandom::mix32	(	uint32_t	state,
		uint32_t	extra
	)

mix some 'extra' entropy into 'state' and return result

Definition at line 20 of file QuasiRandom.cpp.

{
   return mix( state + extra );
}

uint32_t Gaudi::Utils::QuasiRandom::mix64	(	uint32_t	state,
		uint64_t	extra
	)

mix some 'extra' entropy into 'state' and return result

Definition at line 25 of file QuasiRandom.cpp.

{
   typedef boost::low_bits_mask_t<32>  mask_t;
   state = mix32( state , uint32_t( extra        & mask_t::sig_bits_fast) );
   return  mix32( state , uint32_t((extra >> 32) & mask_t::sig_bits_fast) );
}

uint32_t Gaudi::Utils::QuasiRandom::mixString	(	uint32_t	state,
		const std::string &	extra
	)

mix some 'extra' entropy into 'state' and return result

Definition at line 32 of file QuasiRandom.cpp.

{
   // prefix name with ' ' until the size is a multiple of 4.
   std::string s = std::string((4 - extra.size() % 4) % 4, ' ') + extra;
   for (size_t i=0; i < s.size() / 4; ++i) {
      //FIXME: this might do something different on big endian vs. small endian machines...
      uint32_t x = uint32_t(s[i * 4])
         | uint32_t(s[i * 4 + 1]) << 8
         | uint32_t(s[i * 4 + 2]) << 16
         | uint32_t(s[i * 4 + 3]) << 24 ;
      state = mix32(state , x);
   }
   return state;
}