code: func NewCigarOp(t CigarOpType, n int) CigarOp {
  	if uint64(n) > 1<<28-1 {
  		panic("sam: illegal CIGAR op length")
  	}
  	return CigarOp(t) | (CigarOp(n) << 4)
  }
docs: // NewCigarOp returns a CIGAR operation of the specified type with length n.
  // Due to a limitation of the BAM format, CIGAR operation lengths are limited
  // to 2^28-1, and NewCigarOp will panic if n is above this or negative.