DRUM - A C++ Implementation for the URL-seen Test of a Web Crawler

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 Copyright (c) 2009 Leandro T. C. Melo

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#ifndef RABIN_FINGERPRINT_HPP
#define RABIN_FINGERPRINT_HPP

#include <boost/cstdint.hpp>

/*
 * Rabin Fingerprint - Implementation as suggested by Broder
 * (http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.53.6172)
 *
 * - This is based on http://sourceforge.net/projects/webcat/ and
 *   http://sourceforge.net/projects/rabinhash/. However, I thinks there's a bug in the current
 *   webcat version (16-03-2009).
 * - Make sure your compiler is standard complaint regarding array initialization. When it's in the
 *   initialization list of the constructor, default-initialization should be provided. This means
 *   zero-initialization for boost::int64_t.
 */


class RabinFingerprint
{
public:
  RabinFingerprint();
  explicit RabinFingerprint(boost::uint64_t);

  boost::uint64_t Compute(boost::int64_t const* A, std::size_t size)const;
  boost::uint64_t Compute(boost::int32_t const* A, std::size_t size)const;
  boost::uint64_t Compute(boost::int16_t const* A, std::size_t size)const;
  boost::uint64_t Compute(boost::int8_t const* A, std::size_t size)const;
  boost::uint64_t Compute(char const* A, std::size_t size)const;

private:
  //Disable.
  RabinFingerprint(RabinFingerprint const&);
  RabinFingerprint const& operator=(RabinFingerprint const&);

  void InitTables();
  boost::uint64_t & ComputeTablesSum(boost::uint64_t & w)const;

  //It's not necessary to provide definitions for such integral constant variables as long as their
  //addresses are not taken.
  static int const K = 64; //Degree of the polynomial P.
  static boost::int64_t const T_K_minus_1 = 1LL << (K - 1); //Represents t^(K-1).

  //Bit 64 of the polynomial P is always 1 and not treated directly. This is the polynomial
  //with the leading coefficient removed (lcr).
  boost::uint64_t const p_lcr;

  //Broder's paper presents four pre-computed tables because words are considered to be 32-bit.
  //In this implementation W is a 64-bit integral type. Eight tables are used.
  //Table A is i1^127 + i2^126 + ... + i8^120.
  //Table B is i1^119 + i2^118 + ... + i8^112.
  //Table C, D, ..
  //Table E is i1^95  + i2^94  + ... + i8^88. (This is table A in the paper.)
  //Table F, G, H.
  boost::int64_t tableA_[256]; //Assuming byte size 8.
  boost::int64_t tableB_[256];
  boost::int64_t tableC_[256];
  boost::int64_t tableD_[256];
  boost::int64_t tableE_[256];
  boost::int64_t tableF_[256];
  boost::int64_t tableG_[256];
  boost::int64_t tableH_[256];
};

#endif //RABIN_FINGERPRINT_HPP