CRC32CheckSum.hpp

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/*  Visualization Library                                                             */
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#ifndef CRC32CheckSum_INCLUDE_ONCE
#define CRC32CheckSum_INCLUDE_ONCE

#include <vlCore/VirtualFile.hpp>

namespace vl
{
  class CRC32CheckSum
  {
    // Lower this if you need to limit the amount of data allocated to the stack, for example to 16K.
    static const int CHUNK_SIZE = 128*1024;

  public:
    CRC32CheckSum() { crc32_init(); }

    unsigned int compute(const void* buf, int length)
    {
      const unsigned char* buffer = (const unsigned char*)buf;
      mCRC32 = 0xffffffff;
      while(length--)
        mCRC32 = (mCRC32 >> 8) ^ crc32_table[(mCRC32 & 0xFF) ^ *buffer++];
      return mCRC32 ^ 0xffffffff;
    }

    unsigned int compute(VirtualFile* stream)
    {
      std::vector<unsigned char> buffer;
      buffer.resize(CHUNK_SIZE);
      unsigned char *ptr = &buffer.front();
      startCRC32();

      for( int length = (int)stream->read(ptr, CHUNK_SIZE); length; length = (int)stream->read(ptr, CHUNK_SIZE) )
        continueCRC32(ptr,length);

      return finalizeCRC32();
    }

    void startCRC32() { mCRC32 = 0xffffffff; }
    unsigned int finalizeCRC32() { return mCRC32 ^ 0xffffffff; }
    void continueCRC32(unsigned char* ptr, int length)
    {
      while(length--)
        mCRC32 = (mCRC32 >> 8) ^ crc32_table[(mCRC32 & 0xFF) ^ *ptr++];
    }

  protected:
    void crc32_init()
    {
      mCRC32 = 0;
      unsigned int ulPolynomial = 0x04c11db7;
      for(int i = 0; i <= 0xFF; i++)
      {
        crc32_table[i]=reflect(i, 8) << 24;
        for (int j = 0; j < 8; j++)
          crc32_table[i] = (crc32_table[i] << 1) ^ (crc32_table[i] & (1 << 31) ? ulPolynomial : 0);
        crc32_table[i] = reflect(crc32_table[i], 32);
      }
    }

    unsigned int reflect(unsigned int val, char ch)
    {
      unsigned int refl = 0;
      for(int i = 1; i < (ch + 1); i++)
      {
        if(val & 1)
          refl |= 1 << (ch - i);
        val >>= 1;
      }
      return refl;
    }

  protected:
    unsigned int mCRC32;
    unsigned int crc32_table[256];
  };
}

#endif