vhdl

Multiplication of two different bit numbers in VHDL

I have two numbers A and B, both of different sizes and i need to multiply them using VHDL. I don't know the exact logic to multiply them.

Solution

  • If you are trying to multiply two std_logic_vector, then * will fails, since std_logic_vector is just an array of std_logic elements, but does not have an inherit numerical representation.

    So take a look a the ieee.numeric_std VHDL package. This defines unsigned and signed types that assume a typical numerical representation of an array, along with operators on these types, including *. Using this package you can do:

    use ieee.numeric_std.all;
...
c <= std_logic_vector(unsigned(a) * unsigned(b));

    Note that for * the c'length is a'length + b'length.