wksq = Square((idx >> 0) & 0x3F);
bksq = Square((idx >> 6) & 0x3F);
us = Color ((idx >> 12) & 0x01);
psq = File ((idx >> 13) & 0x03) | Rank(RANK_7 - (idx >> 15));
wksq = Square((idx >> 0) & 0x3F);
bksq = Square((idx >> 6) & 0x3F);
us = Color ((idx >> 12) & 0x01);
psq = File ((idx >> 13) & 0x03) | Rank(RANK_7 - (idx >> 15));