package SWISS::CRC64;
   
# ** Initialisation
#32 first bits of generator polynomial for CRC64
#the 32 lower bits are assumed to be zero
my $POLY64REVh = 0xd8000000; 
my @CRCTableh = 256;
my @CRCTablel = 256;
my $initialized;


sub crc64 {	
  my $sequence = shift;
  my $crcl = 0;
  my $crch = 0;
  if (!$initialized) {
    $initialized = 1;
    for (my $i=0; $i<256; $i++) {
      my $partl = $i;
      my $parth = 0;
      for (my $j=0; $j<8; $j++) {
	my $rflag = $partl & 1;
	$partl >>= 1;
	$partl |= (1 << 31) if $parth & 1;
	$parth >>= 1;
	$parth ^= $POLY64REVh if $rflag;
      }
      $CRCTableh[$i] = $parth;
      $CRCTablel[$i] = $partl;
    }
  }
  
  foreach (split '', $sequence) {
    my $shr = ($crch & 0xFF) << 24;
    my $temp1h = $crch >> 8;
    my $temp1l = ($crcl >> 8) | $shr;
    my $tableindex = ($crcl ^ (unpack "C", $_)) & 0xFF;
    $crch = $temp1h ^ $CRCTableh[$tableindex];
    $crcl = $temp1l ^ $CRCTablel[$tableindex];
  }
  return wantarray ? ($crch, $crcl) : sprintf("%08X%08X", $crch, $crcl);
}
    
1;