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//==========================================================================
//--------------------------------------------------------------------------
// Copyright (C) Organisation europeenne pour la Recherche nucleaire (CERN)
// All rights reserved.
//
// For the licensing terms see $DD4hepINSTALL/LICENSE.
// For the list of contributors see $DD4hepINSTALL/doc/CREDITS.
//
// Author : A.Sailer
//
//==========================================================================
#ifndef DDG4_PLUGINS_GEANT4EVENTSEED_H
#define DDG4_PLUGINS_GEANT4EVENTSEED_H
// Framework include files
#include <DDG4/Geant4RunAction.h>
// fallthrough only exists from c++17
#if defined __has_cpp_attribute
#if __has_cpp_attribute(fallthrough)
#define ATTR_FALLTHROUGH [[fallthrough]]
#else
#define ATTR_FALLTHROUGH
#endif
#else
#define ATTR_FALLTHROUGH
#endif
/// Namespace for the AIDA detector description toolkit
/// Namespace for the Geant4 based simulation part of the AIDA detector description toolkit
/**
* \addtogroup Geant4RunActions
* @{
* \package EventSeed
* \brief Set the event seed for each event
*
* This plugins allows one to skip events and still be reproducible.
* We are using jenkins_hash from an intial seed, runID and eventID
* see http://burtleburtle.net/bob/hash/evahash.html
*
* \author A.Sailer
* \version 1.0
/// Plugin class to set the event seed for each event
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class Geant4EventSeed: public Geant4RunAction {
protected:
unsigned int m_initialSeed;
unsigned int m_runID;
std::string m_type;
bool m_initialised;
public:
/// Standard constructor with initializing arguments
Geant4EventSeed(Geant4Context*, const std::string& );
/// Default destructor
virtual ~Geant4EventSeed();
/// begin-of-run callback
void begin(const G4Run*);
/// begin-of-event callback
void beginEvent(const G4Event*);
};
/*
Hashing for random seed as used in Marlin EventSeeder processor
Original source by Bob Jenkins
http://www.burtleburtle.net/bob/hash/doobs.html
Hash a variable-length key into a 32-bit value
*/
#define hashsize(n) ( 1U << (n) )
#define hashmask(n) ( hashsize ( n ) - 1 )
/*
--------------------------------------------------------------------
mix -- mix 3 32-bit values reversibly.
For every delta with one or two bits set, and the deltas of all three
high bits or all three low bits, whether the original value of a,b,c
is almost all zero or is uniformly distributed,
* If mix() is run forward or backward, at least 32 bits in a,b,c
have at least 1/4 probability of changing.
* If mix() is run forward, every bit of c will change between 1/3 and
2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.)
mix() was built out of 36 single-cycle latency instructions in a
structure that could supported 2x parallelism, like so:
a -= b;
a -= c; x = (c>>13);
b -= c; a ^= x;
b -= a; x = (a<<8);
c -= a; b ^= x;
c -= b; x = (b>>13);
...
Unfortunately, superscalar Pentiums and Sparcs can't take advantage
of that parallelism. They've also turned some of those single-cycle
latency instructions into multi-cycle latency instructions. Still,
this is the fastest good hash I could find. There were about 2^^68
to choose from. I only looked at a billion or so.
--------------------------------------------------------------------
*/
#define mix(a,b,c) \
{ \
a -= b; a -= c; a ^= (c>>13); \
b -= c; b -= a; b ^= (a<<8); \
c -= a; c -= b; c ^= (b>>13); \
a -= b; a -= c; a ^= (c>>12); \
b -= c; b -= a; b ^= (a<<16); \
c -= a; c -= b; c ^= (b>>5); \
a -= b; a -= c; a ^= (c>>3); \
b -= c; b -= a; b ^= (a<<10); \
c -= a; c -= b; c ^= (b>>15); \
}
/*
--------------------------------------------------------------------
jenkins_hash() -- hash a variable-length key into a 32-bit value
k : the key (the unaligned variable-length array of bytes)
len : the length of the key, counting by bytes
initval : can be any 4-byte value
Returns a 32-bit value. Every bit of the key affects every bit of
the return value. Every 1-bit and 2-bit delta achieves avalanche.
About 6*len+35 instructions.
The best hash table sizes are powers of 2. There is no need to do
mod a prime (mod is sooo slow!). If you need less than 32 bits,
use a bitmask. For example, if you need only 10 bits, do
h = (h & hashmask(10));
In which case, the hash table should have hashsize(10) elements.
If you are hashing n strings (ub1 **)k, do it like this:
for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);
By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this
code any way you wish, private, educational, or commercial. It's free.
See http://burtleburtle.net/bob/hash/evahash.html
Use for hash table lookup, or anything where one collision in 2^^32 is
acceptable. Do NOT use for cryptographic purposes.
--------------------------------------------------------------------
*/
unsigned jenkins_hash ( unsigned char *k, unsigned length, unsigned initval )
{
unsigned a, b;
unsigned c = initval;
unsigned len = length;
a = b = 0x9e3779b9;
while ( len >= 12 ) {
a += ( k[0] + ( (unsigned)k[1] << 8 )
+ ( (unsigned)k[2] << 16 )
+ ( (unsigned)k[3] << 24 ) );
b += ( k[4] + ( (unsigned)k[5] << 8 )
+ ( (unsigned)k[6] << 16 )
+ ( (unsigned)k[7] << 24 ) );
c += ( k[8] + ( (unsigned)k[9] << 8 )
+ ( (unsigned)k[10] << 16 )
+ ( (unsigned)k[11] << 24 ) );
mix ( a, b, c );
k += 12;
len -= 12;
}
c += length;
switch ( len ) {
case 11: c += ( (unsigned)k[10] << 24 ); ATTR_FALLTHROUGH;
case 10: c += ( (unsigned)k[9] << 16 ); ATTR_FALLTHROUGH;
case 9 : c += ( (unsigned)k[8] << 8 ); ATTR_FALLTHROUGH;
/* First byte of c reserved for length */
case 8 : b += ( (unsigned)k[7] << 24 ); ATTR_FALLTHROUGH;
case 7 : b += ( (unsigned)k[6] << 16 ); ATTR_FALLTHROUGH;
case 6 : b += ( (unsigned)k[5] << 8 ); ATTR_FALLTHROUGH;
case 5 : b += k[4]; ATTR_FALLTHROUGH;
case 4 : a += ( (unsigned)k[3] << 24 ); ATTR_FALLTHROUGH;
case 3 : a += ( (unsigned)k[2] << 16 ); ATTR_FALLTHROUGH;
case 2 : a += ( (unsigned)k[1] << 8 ); ATTR_FALLTHROUGH;
case 1 : a += k[0];
}
mix ( a, b, c );
return c;
}
/// calculate hash from initialSeed, eventID and runID
unsigned int hash( unsigned int initialSeed, unsigned int eventNumber, unsigned int runNumber ){
unsigned int seed = 0;
unsigned char * c = (unsigned char *) &eventNumber ;
seed = jenkins_hash( c, sizeof eventNumber, seed) ;
c = (unsigned char *) &runNumber ;
seed = jenkins_hash( c, sizeof runNumber, seed) ;
c = (unsigned char *) &initialSeed ;
seed = jenkins_hash( c, sizeof initialSeed, seed) ;
return seed;
}
} // End namespace sim
} // End namespace dd4hep