bloom_filter.h

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/******************************************************************************
The MIT License(MIT)
 
Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com
 
Copyright(c) 2014 John Wellbelove
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files(the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
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furnished to do so, subject to the following conditions :
 
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
 
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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******************************************************************************/
 
#ifndef ETL_BLOOM_FILTER_INCLUDED
#define ETL_BLOOM_FILTER_INCLUDED
 
#include "platform.h"
#include "binary.h"
#include "bitset.h"
#include "log.h"
#include "parameter_type.h"
#include "power.h"
#include "type_traits.h"

 
namespace etl
{
  namespace private_bloom_filter
  {
    // Placeholder null hash for defaulted template parameters.
    struct null_hash
    {
      template <typename T>
      size_t operator()(T)
      {
        return 0;
      }
    };
  } // namespace private_bloom_filter
 
  //***************************************************************************
  //***************************************************************************
  template <size_t Desired_Width, typename THash1, typename THash2 = private_bloom_filter::null_hash,
            typename THash3 = private_bloom_filter::null_hash>
  class bloom_filter
  {
  private:
 
    typedef typename etl::parameter_type<typename THash1::argument_type>::type parameter_t;
    typedef private_bloom_filter::null_hash                                    null_hash;
 
  public:
 
    enum
    {
      // Make the most efficient use of the bitset.
      WIDTH = etl::bitset<Desired_Width>::Allocated_Bits
    };
 
    //***************************************************************************
    //***************************************************************************
    void clear()
    {
      flags.reset();
    }
 
    //***************************************************************************
    //***************************************************************************
    void add(parameter_t key)
    {
      flags.set(get_hash<THash1>(key));
 
      if (!etl::is_same<THash2, null_hash>::value)
      {
        flags.set(get_hash<THash2>(key));
      }
 
      if (!etl::is_same<THash3, null_hash>::value)
      {
        flags.set(get_hash<THash3>(key));
      }
    }
 
    //***************************************************************************
    //***************************************************************************
    bool exists(parameter_t key) const
    {
      bool exists1 = flags[get_hash<THash1>(key)];
      bool exists2 = true;
      bool exists3 = true;
 
      // Do we have a second hash?
      if (!etl::is_same<THash2, null_hash>::value)
      {
        exists2 = flags[get_hash<THash2>(key)];
      }
 
      // Do we have a third hash?
      if (!etl::is_same<THash3, null_hash>::value)
      {
        exists3 = flags[get_hash<THash3>(key)];
      }
 
      return exists1 && exists2 && exists3;
    }
 
    //***************************************************************************
    //***************************************************************************
    size_t width() const
    {
      return WIDTH;
    }
 
    //***************************************************************************
    //***************************************************************************
    size_t usage() const
    {
      return (100 * count()) / WIDTH;
    }
 
    //***************************************************************************
    //***************************************************************************
    size_t count() const
    {
      return flags.count();
    }
 
  private:
 
    //***************************************************************************
    //***************************************************************************
    template <typename THash>
    size_t get_hash(parameter_t key) const
    {
      size_t hash = THash()(key);
 
      // Fold the hash down to fit the width.
      return fold_bits<size_t, etl::log2<WIDTH>::value>(hash);
    }

    etl::bitset<WIDTH> flags;
  };
} // namespace etl
 
#endif