U64 nextBit( U64 **p, U8 *o ) {                  // p: pointer to pointer to current quad; o: pointer to current offset
    if( ++( *o ) == 64 ) {                       // increment the offset and detect transitions across quad boundaries.
        *o = 0;                                  // reset the offset.
        ++*p;                                    // increment the quad pointer.
    }
    // Get the 'current' (unshifted) quad value; and the next
    return __shiftleft128( *( *p + 1 ), **p, *o );         // return the value from the higher location with *o bits from lo shifted in from the right.
}