code: func (b *OpenBitSet) Clear(index int64) {
  	wordNum := int(index >> 6) // div 64
  	if wordNum >= b.wlen {
  		return
  	}
  	bitmask := int64(1) << uint64(index)
  	b.bits[wordNum] &= ^bitmask
  }
docs: /* Clears a bit, allowing access beyond the current set size without changing the size. */