etl/include/etl/pearson.h

///\file

/******************************************************************************
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
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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
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
******************************************************************************/

#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

///\defgroup pearson Pearson hash calculation
///\ingroup pearson

namespace etl
{
  //***************************************************************************
  /// Calculates a Pearson hash
  ///\tparam HASH_LENGTH The number of elements in the hash.
  /// \ingroup pearson
  //***************************************************************************
  template <size_t HASH_LENGTH>
  class pearson
  {
  public:

    typedef etl::array<uint8_t, HASH_LENGTH> value_type;

    //*************************************************************************
    /// Default constructor.
    //*************************************************************************
    pearson()
      : first(true)
    {
      reset();
    }

    //*************************************************************************
    /// Constructor from range.
    /// \param begin Start of the range.
    /// \param end   End of the range.
    //*************************************************************************
    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);
    }

    //*************************************************************************
    /// Resets the hash to the initial state.
    //*************************************************************************
    void reset()
    {
      hash.fill(0);
      first = true;
    }

    //*************************************************************************
    /// Adds a range.
    /// \param begin
    /// \param end
    //*************************************************************************
    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;
      }
    }

    //*************************************************************************
    /// \param value The char to add to the hash.
    //*************************************************************************
    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_];
        }
      }
    }

    //*************************************************************************
    /// Gets the hash value.
    //*************************************************************************
    value_type value() const
    {
      return hash;
    }

    //*************************************************************************
    /// Conversion operator to value_type.
    //*************************************************************************
    operator value_type() const
    {
      return value();
    }

  private:

    bool       first;
    value_type hash;
  };
} // namespace etl

#endif