CRC32.c

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#include "libFireBird.h"
 
dword                   CRC32Table[256];
bool                    CRCTableOK = FALSE;
 
void make_crc_table(void);
 
void make_crc_table(void)
{
  TRACEENTER();
 
  dword                dwCRC;
  dword                CRCPOLY = 0;
  dword                i, j;
  bool                 topbit;
  byte                 poly[15] = { 0, 1, 2, 4, 5, 7, 8, 10, 11, 12, 16, 22, 23, 26 };
 
  for(i = 0; i < 15; ++i)
    CRCPOLY |= (1 << poly[i]);
 
  for(i = 0; i < 256; i++)
  {
    dwCRC = i << 24;
    for(j = 0; j < 8; ++j)
    {
      topbit = (dwCRC >> 31);
      dwCRC <<= 1;
      if(topbit) dwCRC ^= CRCPOLY;
    }
    CRC32Table[i] = dwCRC;
  }
  CRCTableOK = TRUE;
 
  TRACEEXIT();
}
 
 
dword CRC32(dword StartValue, void *StartAddress, dword Length)
{
  TRACEENTER();
 
  volatile byte         *pData;
  dword                 crc = StartValue;   //Normaly 0xffffffff
 
  if(!StartAddress)
  {
    TRACEEXIT();
    return crc;
  }
 
  if(!CRCTableOK) make_crc_table();
 
  for(pData = StartAddress; pData < (byte *) StartAddress + Length; pData++)
    crc = (crc << 8) ^ CRC32Table[((crc >> 24) ^ *pData) & 0xff];
 
  TRACEEXIT();
  return crc;
}