PC_FREE0
static const uint64_t pc_freemask[_NPCM] = { PC_FREE0, PC_FREE1 };
pc->pc_map[0] = PC_FREE0;
if (pc->pc_map[0] == PC_FREE0 && pc->pc_map[1] == PC_FREE1) {
if (pc->pc_map[0] != PC_FREE0 || pc->pc_map[1] != PC_FREE1) {
pc->pc_map[0] = PC_FREE0 & ~1ul; /* preallocated bit 0 */