etl/crc16.h

///\file

/******************************************************************************
The MIT License(MIT)

Embedded Template Library.

Copyright(c) 2014 jwellbelove

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files(the "Software"), to deal
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******************************************************************************/

#ifndef __ETL_CRC16__
#define __ETL_CRC16__

#include <cstdint>

///\defgroup crc16 Sixteen bit CRC calculation
///\ingroup crc

namespace etl
{
  //***************************************************************************
  /// CRC16 table
  /// \ingroup crc16
  //***************************************************************************
  extern const uint16_t CRC16[];

  //***************************************************************************
  /// Calculates CRC16 using polynomial 0x8005.
  /// \ingroup crc16
  //***************************************************************************
  class crc16
  {
  public:

    typedef uint16_t value_type;

    //*************************************************************************
    /// Default constructor.
    //*************************************************************************
    crc16()
    {
      reset();
    }

    //*************************************************************************
    /// Constructor from range.
    /// \param begin Start of the range.
    /// \param end   End of the range.
    /// \return The CRC result.
    //*************************************************************************
    template<typename TIterator>
    crc16(TIterator begin, const TIterator end)
    {
      reset();
      add(begin, end);
    }

    //*************************************************************************
    /// Resets the CRC to the initial state.
    //*************************************************************************
    void reset()
    {
      crc = 0;
    }

    //*************************************************************************
    /// \param value The value to add to the CRC.
    /// \return The CRC result.
    //*************************************************************************
    template<typename TValue>
    void add(TValue value)
    {
      // How many steps in a value?
      size_t steps = sizeof(TValue) / sizeof(uint8_t);

      uint8_t* p_data = reinterpret_cast<uint8_t*>(&value);

      for (size_t i = 0; i < steps; ++i)
      {
        crc = (crc >> 8) ^ CRC16[(crc ^ p_data[i]) & 0xFF];
      }
    }

    //*************************************************************************
    /// \param begin Start of the range.
    /// \param end   End of the range.
    /// \return The CRC result.
    //*************************************************************************
    template<typename TIterator>
    void add(TIterator begin, const TIterator end)
    {
      while (begin != end)
      {
        add(*begin);
        ++begin;
      }
    }

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

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

  private:

    value_type crc;
  };
}

#endif