etl/murmur3.h

///\file

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

Embedded Template Library.
https://github.com/ETLCPP/etl

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_MURMUR3__
#define __ETL_MURMUR3__

#include <stdint.h>

#include "endian.h"
#include "ihash.h"
#include "binary.h"
#include "error_handler.h"

#if defined(COMPILER_KEIL)
#pragma diag_suppress 1300
#endif

///\defgroup murmur3 Murmur3 hash calculations
///\ingroup maths

namespace etl
{
  //***************************************************************************
  /// Calculates the murmur3_32 hash.
  /// See https://en.wikipedia.org/wiki/MurmurHash for more details.
  ///\tparam ENDIANNESS The endianness of the calculation for input types larger than uint8_t. Default = endian::little.
  ///\ingroup murmur3_32
  //***************************************************************************
  template <const int ENDIANNESS = endian::little>
  class murmur3_32 : public etl::ihash
  {
  public:

    typedef uint32_t value_type;

    //*************************************************************************
    /// Default constructor.
    /// \param seed The seed value. Default = 0.
    //*************************************************************************
    murmur3_32(value_type seed = 0)
      : seed(seed),
        ihash(etl::endian(ENDIANNESS))
    {
      reset();
    }

    //*************************************************************************
    /// Constructor from range.
    /// \param begin Start of the range.
    /// \param end   End of the range.
    /// \param seed  The seed value. Default = 0.
    //*************************************************************************
    template<typename TIterator>
    murmur3_32(TIterator begin, const TIterator end, value_type seed = 0)
      : seed(seed), 
        ihash(etl::endian(ENDIANNESS))
    {
      reset();
      add(begin, end);
    }

    //*************************************************************************
    /// Resets the hash to the initial state.
    //*************************************************************************
    void reset()
    {
      hash             = seed;
      char_count       = 0;
      block            = 0;
      block_fill_count = 0;
      is_finalised     = false;
    }

    //*************************************************************************
    /// Adds a range.
    /// \param begin
    /// \param end
    //*************************************************************************
    template<typename TIterator>
    void add(TIterator begin, const TIterator end)
    {
      ihash::add(begin, end);
    }

    //*************************************************************************
    /// Adds a value.
    /// \param value The value to add to the hash.
    //*************************************************************************
    template<typename TValue>
    void add(TValue value)
    {
      ihash::add(value);
    }

    //*************************************************************************
    /// Adds a uint8_t value.
    /// If the hash has already been finalised then a 'hash_finalised' error will be emitted.
    /// \param value The char to add to the hash.
    //*************************************************************************
    void add(uint8_t value)
    {
      // We can't add to a finalised hash!
      if (is_finalised)
      {
        ETL_ERROR(hash_finalised());
      }
      else
      {
        block |= value << (block_fill_count * 8);

        if (++block_fill_count == FULL_BLOCK)
        {
          add_block();
          block_fill_count = 0;
          block = 0;
        }

        ++char_count;
      }
    }

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

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

    //*************************************************************************
    /// Gets the generic digest value.
    //*************************************************************************
    generic_digest digest()
    {
      finalise();
      return ihash::get_digest(hash);
    }

  private:

    //*************************************************************************
    /// Adds a filled block to the hash.
    //*************************************************************************
    void add_block()
    {
      block *= CONSTANT1;
      block = rotate_left(block, SHIFT1);
      block *= CONSTANT2;

      hash ^= block;
      hash = rotate_left(hash, SHIFT2);
      hash = (hash * MULTIPLY) + ADD;
    }

    //*************************************************************************
    /// Finalises the hash.
    //*************************************************************************
    void finalise()
    {
      if (!is_finalised)
      {
        block *= CONSTANT1;
        block = rotate_left(block, SHIFT1);
        block *= CONSTANT2;

        hash ^= block;
        hash ^= char_count;
        hash ^= (hash >> 16);
        hash *= 0x85EBCA6B;
        hash ^= (hash >> 13);
        hash *= 0xC2B2AE35;
        hash ^= (hash >> 16);

        is_finalised = true;
      }
    }

    bool       is_finalised;
    uint8_t    block_fill_count;
    size_t     char_count;
    value_type block;
    value_type hash;
    value_type seed;

    static const uint8_t    FULL_BLOCK = 4;
    static const value_type CONSTANT1  = 0xCC9E2D51;
    static const value_type CONSTANT2  = 0x1B873593;
    static const value_type SHIFT1     = 15;
    static const value_type SHIFT2     = 13;
    static const value_type MULTIPLY   = 5;
    static const value_type ADD        = 0xE6546B64;
  };
}

#endif // MURMUR3_H