signed/unsigned multipliers

Not commenting at all on the logistics of signed/unsigned multiplications, but more on synthesizable code, if you write:

signal sum : signed(3 downto 0);

IF(inc = '1') THEN

sum <= sum + 1;

ELSIF(dec = '1') THEN

sum <= sum - 1;

ELSE

sum <= sum;

END IF;

It will usually generate two adders and then mux the output together. However, if you were to write:

signal inc : integer range -1 to 1;

signal sum : signed(3 downto 0);

inc <= -1 when dec = '1' else

1 when inc = '1' else

0;

sum <= sum + inc;

Then it will usually generate a single adder with a mux at one of the input ports.

Obviously the summation should be in a clocked process, but i am being lazy.

Just a thought.

Kevin