code: func NewOpenBitSetOf(numBits int64) *OpenBitSet {
  	assert(numBits > 0)
  	bits := make([]int64, bits2words(numBits))
  	return &OpenBitSet{
  		numBits: numBits,
  		bits:    bits,
  		wlen:    len(bits),
  	}
  }
docs: /* Constructs an OpenBitSet large enough to hold numBits. */