pearson.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
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The above copyright notice and this permission notice shall be included in all
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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******************************************************************************/
 
#ifndef ETL_PEARSON_INCLUDED
#define ETL_PEARSON_INCLUDED
 
#include "platform.h"
#include "array.h"
#include "ihash.h"
#include "iterator.h"
#include "static_assert.h"
#include "type_traits.h"
 
#include <stdint.h>
 
ETL_STATIC_ASSERT(ETL_USING_8BIT_TYPES, "This file does not currently support targets with no 8bit type");
 
#if defined(ETL_COMPILER_KEIL)
  #pragma diag_suppress 1300
#endif

 
namespace etl
{
  //***************************************************************************
  //***************************************************************************
  template <size_t HASH_LENGTH>
  class pearson
  {
  public:
 
    typedef etl::array<uint8_t, HASH_LENGTH> value_type;
 
    //*************************************************************************
    //*************************************************************************
    pearson()
      : first(true)
    {
      reset();
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename TIterator>
    pearson(TIterator begin, const TIterator end)
      : first(true)
    {
      ETL_STATIC_ASSERT(sizeof(typename etl::iterator_traits<TIterator>::value_type) == 1, "Type not supported");
 
      reset();
      add(begin, end);
    }
 
    //*************************************************************************
    //*************************************************************************
    void reset()
    {
      hash.fill(0);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename TIterator>
    void add(TIterator begin, const TIterator end)
    {
      ETL_STATIC_ASSERT(sizeof(typename etl::iterator_traits<TIterator>::value_type) == 1, "Type not supported");
 
      while (begin != end)
      {
        add(static_cast<uint8_t>(*begin));
        ++begin;
      }
    }
 
    //*************************************************************************
    //*************************************************************************
    void add(uint8_t value_)
    {
      static ETL_CONSTANT uint8_t PEARSON_LOOKUP[] = {
        228, 39,  61,  95,  227, 187, 0,   197, 31,  189, 161, 222, 34,  15,  221, 246, 19,  234, 6,   50,  113, 3,   91,  63,  77,  245,
        144, 2,   183, 196, 25,  226, 97,  126, 48,  59,  217, 4,   100, 145, 12,  88,  203, 149, 80,  154, 38,  27,  224, 218, 158, 115,
        202, 79,  53,  83,  242, 36,  139, 131, 136, 191, 42,  170, 23,  99,  156, 51,  143, 60,  233, 206, 62,  108, 17,  67,  81,  71,
        93,  195, 26,  231, 247, 96,  24,  200, 176, 209, 152, 212, 138, 165, 75,  185, 130, 248, 125, 110, 10,  116, 201, 90,  69,  204,
        85,  251, 78,  157, 47,  184, 169, 141, 134, 230, 89,  21,  146, 46,  55,  128, 148, 207, 216, 11,  114, 199, 103, 102, 166, 244,
        5,   104, 225, 160, 132, 28,  172, 65,  121, 140, 153, 119, 198, 210, 58,  87,  117, 177, 33,  22,  13,  37,  49,  174, 109, 40,
        73,  211, 18,  167, 164, 252, 168, 74,  30,  173, 35,  98,  66,  193, 94,  175, 86,  54,  179, 122, 220, 151, 192, 29,  133, 254,
        155, 127, 240, 232, 190, 180, 8,   68,  236, 20,  137, 92,  219, 208, 52,  250, 147, 142, 111, 112, 120, 45,  135, 255, 123, 229,
        57,  182, 243, 124, 186, 253, 7,   237, 9,   16,  70,  171, 235, 107, 223, 118, 215, 178, 194, 181, 43,  188, 106, 105, 64,  241,
        84,  238, 159, 44,  32,  76,  213, 163, 150, 101, 129, 14,  249, 205, 214, 1,   41,  56,  162, 72,  239, 82};
 
      if (first)
      {
        for (size_t i = 0UL; i < HASH_LENGTH; ++i)
        {
          hash[i] = PEARSON_LOOKUP[(uint32_t(value_) + i) % 256];
        }
 
        first = false;
      }
      else
      {
        for (size_t i = 0UL; i < HASH_LENGTH; ++i)
        {
          hash[i] = PEARSON_LOOKUP[hash[i] ^ value_];
        }
      }
    }
 
    //*************************************************************************
    //*************************************************************************
    value_type value() const
    {
      return hash;
    }
 
    //*************************************************************************
    //*************************************************************************
    operator value_type() const
    {
      return value();
    }
 
  private:
 
    bool       first;
    value_type hash;
  };
} // namespace etl
 
#endif