crc32.h

// //////////////////////////////////////////////////////////
// crc32.h
// Copyright (c) 2014,2015 Stephan Brumme. All rights reserved.
// see http://create.stephan-brumme.com/disclaimer.html
//

#pragma once

//#include "hash.h"
#include <string>

// define fixed size integer types
#ifdef _MSC_VER
// Windows
typedef unsigned __int8  uint8_t;
typedef unsigned __int32 uint32_t;
#else
// GCC
#include <stdint.h>
#endif


/// compute CRC32 hash, based on Intel's Slicing-by-8 algorithm
/** Usage:
    CRC32 crc32;
    std::string myHash  = crc32("Hello World");     // std::string
    std::string myHash2 = crc32("How are you", 11); // arbitrary data, 11 bytes

    // or in a streaming fashion:

    CRC32 crc32;
    while (more data available)
      crc32.add(pointer to fresh data, number of new bytes);
    std::string myHash3 = crc32.getHash();

    Note:
    You can find code for the faster Slicing-by-16 algorithm on my website, too:
    http://create.stephan-brumme.com/crc32/
    Its unrolled version is about twice as fast but its look-up table doubled in size as well.
  */
class CRC32 //: public Hash
{
public:
  /// hash is 4 bytes long
  enum { HashBytes = 4 };

  /// same as reset()
  CRC32();

  /// compute CRC32 of a memory block
  std::string operator()(const void* data, size_t numBytes);
  /// compute CRC32 of a string, excluding final zero
  std::string operator()(const std::string& text);

  /// add arbitrary number of bytes
  void add(const void* data, size_t numBytes);

  /// return latest hash as 8 hex characters
  std::string getHash();
  /// return latest hash as bytes
  void        getHash(unsigned char buffer[HashBytes]);

  /// restart
  void reset();

private:
  /// hash
  uint32_t m_hash;
};