hash_utils::murmurhash2 Struct Reference

#include <hash.h>

List of all members.

Public Member Functions
	murmurhash2 (UInt_t seed)
UInt_t	operator() (const void *key, int len) const
Public Attributes
const UInt_t	fSeed

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Detailed Description

Functor copy of murmurhash2 (Public Domain / MIT liscence) by Austin Appleby If it's good enoiugh for gcc...

Definition at line 10 of file hash.h.

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Constructor & Destructor Documentation

hash_utils::murmurhash2::murmurhash2

(

UInt_t

seed

)

[inline]

Definition at line 11 of file hash.h.

: fSeed(seed) {};

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Member Function Documentation

UInt_t hash_utils::murmurhash2::operator()	(	const void *	key,
		int	len
	)			const

Definition at line 4 of file hash.cpp.

References fSeed.

{
  // 'm' and 'r' are mixing constants generated offline.
  // They're not really 'magic', they just happen to work well.
  const UInt_t m = 0x5bd1e995;
  const Int_t r = 24;
  
  // Initialize the hash to a 'random' value
  UInt_t h = fSeed ^ len;
  
  // Mix 4 bytes at a time into the hash
  const Byte_t* data = (const Byte_t*) key;
  
  while(len >= 4){
    UInt_t k = *(UInt_t *)data;
    
    k *= m; 
    k ^= k >> r; 
    k *= m; 
    
    h *= m; 
    h ^= k;
    
    data += 4;
    len -= 4;
  }
  
  // Handle the last few bytes of the input array 
  // fallthrough is intended 
  switch(len) {
  case 3: h ^= data[2] << 16; 
  case 2: h ^= data[1] << 8;
  case 1: h ^= data[0];
    h *= m;
  };
  
  // Do a few final mixes of the hash to ensure the last few
  // bytes are well-incorporated.
  h ^= h >> 13;
  h *= m;
  h ^= h >> 15;
  
  return h;
}

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Member Data Documentation

const UInt_t hash_utils::murmurhash2::fSeed

Definition at line 13 of file hash.h.

Referenced by operator()().

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The documentation for this struct was generated from the following files:

• rootana/src/framework/hash.h
• rootana/src/framework/hash.cpp