vhdl multiply
First, if you are intending to use a fractional fixed notation like xxx.xxx, then you can perform multiplication by shifting each operand to the left by 8 and consider them as integers .Then, you can perform integer multiplication which can be performed by "*" .After finishing the multiplication, you must shift the result by 16 because you shifted each operand by 8 .If you only need 8 bits after the point, you can simply discard the rest of bits .
You can also use the IEEE floating point notation i.e you can represent the number as a sign ,exponent and magnitude .You simply multiply the magnitudes together and add the exponents .Note that this formats considers the number as 1.xxxeyyy i.e after magnitude multiplication, you may need to perform shifting till you achieve only 1 before the point ,and add the number of shifts to the exponent .
If your numbers' range is small I'd recommend the fixed point notation, but if you're expecting your system to handle large values of numbers, then you should consider the floating point notation .