'operation' : unsafe mix of type 'type' and signed bitfield of type 'type'
This warning is generated when comparing a one-bit signed bit field to a bool variable. Since a one-bit signed bit field can only contain the values -1 or 0, it is dangerous to compare it to bool. No warnings are generated about mixing bool and one-bit unsigned bitfields since they are identical to bool and can only hold 0 or 1.