_BITS
#define _PC_N ((_PC_LAST + _BITS - 1) / _BITS)
#define _PC_ISSET(n, a) (a[(n) / _BITS] & (1 << ((n) % _BITS)))
#define _PC_SET(n, a) (a[(n) / _BITS] |= (1 << ((n) % _BITS)))