hash.hpp

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/*
 * Copyright (c) 2013, Lawrence Livermore National Security, LLC. 
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 * Written by Roger Pearce <rpearce@llnl.gov>. 
 * LLNL-CODE-644630. 
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#ifndef HAVOQGT_DETAIL_HASH_HPP_INCLUDED
#define HAVOQGT_DETAIL_HASH_HPP_INCLUDED

#include <stdint.h>

namespace havoqgt { namespace detail {

inline uint32_t hash32( uint32_t a)
{
   a = (a+0x7ed55d16) + (a<<12);
   a = (a^0xc761c23c) ^ (a>>19);
   a = (a+0x165667b1) + (a<<5);
   a = (a+0xd3a2646c) ^ (a<<9);
   a = (a+0xfd7046c5) + (a<<3);
   a = (a^0xb55a4f09) ^ (a>>16);
   return a;
}

inline uint16_t hash16( uint16_t a)
{
   a = (a+0x5d16) + (a<<6);
   a = (a^0xc23c) ^ (a>>9);
   a = (a+0x67b1) + (a<<5);
   a = (a+0x646c) ^ (a<<7);
   a = (a+0x46c5) + (a<<3);
   a = (a^0x4f09) ^ (a>>8);
   return a;
}

inline uint64_t shifted_n_hash32(uint64_t input, int n) {
  uint64_t to_hash = input >> n;
  uint64_t mask    = 0xFFFFFFFF;
  to_hash &= mask;
  to_hash = hash32(to_hash);

  to_hash <<= n;
  mask    <<= n;
  //clear bits
  input &= ~mask;
  input |= to_hash;
  return input;
}

inline uint64_t shifted_n_hash16(uint64_t input, int n) {
  uint64_t to_hash = input >> n;
  uint64_t mask    = 0xFFFF;
  to_hash &= mask;
  to_hash = hash16(to_hash);

  to_hash <<= n;
  mask    <<= n;
  //clear bits
  input &= ~mask;
  input |= to_hash;
  return input;
}

inline uint64_t hash_nbits(uint64_t input, int n) {
  //std::cout << "hash_nbits(" << input << ", " << n << ") = ";
  if(n==32) {
    input =  hash32(input);
  } else if(n>32){
    assert(n>32);
    n -= 32;
    for(int i=0; i<=n; ++i) {
      input = shifted_n_hash32(input, i);
    }
    for(int i=n; i>=0; --i) {
      input = shifted_n_hash32(input, i);
    }
  } else if(n<32) {
    assert(n<32);
    assert(n>16 && "Hashing less than 16bits is not supported");
    n -= 16;
    for(int i=0; i<=n; ++i) {
      input = shifted_n_hash16(input, i);
    }
    for(int i=n; i>=0; --i) {
      input = shifted_n_hash16(input, i);
    }
  }
  //std::cout << input << std::endl;
  return input;
}


}} // end namespace havoqgt::detail



#endif