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vhdlfpga

Multiply and add operators in vhdl

Is there any library in vhdl that defines * and + operators? I need to multiply and add more than 128 bit numbers .if yes, are they sythesizable?. Please help.

Solution

  • Yes. For example:

    library ieee;
use ieee.numeric_std.all;

...

  signal a : signed(31 downto 0); -- 32-bit signed value
  signal b : signed(7 downto 0);  -- 8-bit signed value
  signal c : signed(39 downto 0); -- 40-bit signed value

...

  c <= a * b;  -- Note 'c' is as wide as the sum of a's length and b's length

    The numeric_std package defines unsigned and signed types. It also defines operators for these as well. Note it is also permissible (subject to some restrictions) to mix signed and unsigned with integers and naturals. For example:

      signal a : signed(31 downto 0);
  signal b : signed(31 downto 0);

...

  b <= a * 17;  -- Multiply by a constant

    Care must be taken in these cases to ensure overflow does not occur.

    And these are synthesizable (we use them all the time in real designs).