void flip(long index) {
		assert index >= 0 && index < numBits : "index=" + index + " numBits=" + numBits;
		int wordNum = (int) (index >> 6); // div 64
		long bitmask = 1L << index; // mod 64 is implicit
		bits[wordNum] ^= bitmask;
	}
void flip ( long index ) { assert index >= 0 && index < numBits : "index=" + index + " numBits=" + numBits ; int wordNum = ( int ) ( index > > 6 ) ; long bitmask = 1L << index ; bits [ wordNum ] ^= bitmask ; }
Flip the bit at the provided index.