Fixed-point multiplication with "altmult_complex" megafunction

The answer is yes to both of your questions, unless you multiply the two maximum negative numbers.

Even more useful is the fixed point rules. If you have a 16 bit number with 8 bit integer and 8 bits fraction, you multiply it by a 10 bit number with 3 bits integer and 7 bits fractional, you get an 11.15 bit result. You simply add together the integer and fraactional bits.