CRC32.cpp

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#include <CRC32.h>
bool CRC32::calculated = false;
u_int32_t CRC32::crc_table[256];
CRC32::CRC32()
{
  if(!calculated)
  {
    calculated = true;
    calcCrcTable();
  }
}


CRC32::~CRC32()
{
}


u_int32_t CRC32::calc(const char *data, unsigned int size)
{
  u_int32_t crc = 0xFFFFFFFF;
  for (unsigned int i = 0; i < size; i++)
  {
    crc = crc_table[(crc ^ (data[i])) & 0xFF] ^ (crc >> 8);
  }
  crc = ~crc;
  return crc;
}


void CRC32::calcCrcTable()
{
  const u_int32_t CRCPOLY = 0xEDB88320;
  register u_int32_t t;
  for (register unsigned int i = 0; i < 256; i++)
  {
    t = i;
    for (register int j = 8; j > 0; j--)
    {
      if (t & 1)
        t = (t >> 1) ^ CRCPOLY;
      else
        t >>= 1;
    }
    crc_table[i] = t;
  }
}