Compute CRC for POSNET fiscal printers

gistfile1.cs

    private static readonly Encoding encoding = Encoding.GetEncoding( 1250 );

    static readonly ushort[] Table = new ushort[256];
    static bool przeliczone = false;

    void fillTable() {

      for( int i = 0; i < Table.Length; ++i ) {
        ushort num2 = 0;
        ushort num3 = (ushort)( i << 8 );
        for( int j = 0; j < 8; ++j ) {
          if( ( ( num2 ^ num3 ) & 0x8000 ) != 0 ) {
            num2 = (ushort)( ( num2 << 1 ) ^ 0x1021 );
          } else {
            num2 = (ushort)( num2 << 1 );
          }
          num3 = (ushort)( num3 << 1 );
        }
        Table[i] = num2;
      }

    }

    byte[] computeCRC( byte[] buffer ) {
      if( !przeliczone ) {
        fillTable();
        przeliczone = true;
      }

      ushort num = 0;
      for( int i = 0; i < buffer.Length; i++ ) {
        num = (ushort)( ( num << 8 ) ^ Table[( num >> 8 ) ^ ( 0xff & buffer[i] )] );
      }

      return encoding.GetBytes( String.Format( "{0:X4}", num ) );
    }