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
copies of the Software, and to permit persons to whom the Software is
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.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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SOFTWARE.
******************************************************************************/
 
#ifndef ETL_BLOOM_FILTER_INCLUDED
#define ETL_BLOOM_FILTER_INCLUDED
 
#include "platform.h"
#include "parameter_type.h"
#include "bitset.h"
#include "type_traits.h"
#include "binary.h"
#include "log.h"
#include "power.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;
      }
    };
  }
 
  //***************************************************************************
  //***************************************************************************
  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;
  };
}
 
#endif