SW_Top_Shift
((S387->swd & ~SW_Top & 0xffff) | ((S387->ftop << SW_Top_Shift) & SW_Top))
S387->ftop = (S387->swd >> SW_Top_Shift) & 7;
top = (partial_status >> SW_Top_Shift) & 7;
((partial_status & ~SW_Top & 0xffff) | ((top << SW_Top_Shift) & SW_Top))