VHDL code for logarithme

Altera_Forum · ‎09-26-2011

Hi,

There are somoene that release a vhdl code for log or have any idea about it.

I need any tutorial or helps to start release it.

Thank you.

Altera_Forum · ‎09-26-2011

like log base 2?

this function will return the nearest log2 of a number (but I wouldnt recommend synthesising as a real time function) Its useful for determining how many bits you need for a vector.


function log2(x : integer) return integer is
  variable temp : integer :=x;
  variable n : integer := 1;
begin
  while temp > 1 loop
    temp := temp/2;
    n := n + 1;
  end loop;
 
  return n;
end function log2;

Altera_Forum · ‎09-26-2011

--- Quote Start ---

like log base 2?

this function will return the nearest log2 of a number (but I wouldnt recommend synthesising as a real time function) Its useful for determining how many bits you need for a vector.


function log2(x : integer) return integer is
  variable temp : integer :=x;
  variable n : integer := 1;
begin
  while temp > 1 loop
    temp := temp/2;
    n := n + 1;
  end loop;
 
  return n;
end function log2;

--- Quote End ---

Think you very much for your reply,

ok for this function it is clear, but that i need is a function that can execute during a minimum of clock cycle.

ThAnk you

Altera_Forum · ‎09-26-2011

if you need a synthesisable version, I suggest you use a look-up table.

Altera_Forum · ‎09-27-2011

--- Quote Start ---

if you need a synthesisable version, I suggest you use a look-up table.

--- Quote End ---

Ok thank you, already i use LUT, but i search if it is possible to find a synthetisable code for log.

Altera_Forum · ‎09-27-2011

LUT is the easiest. But you should be able to generate the table using a function.

Altera_Forum · ‎09-27-2011

--- Quote Start ---

LUT is the easiest. But you should be able to generate the table using a function.

--- Quote End ---

I generate the LUT through Matlab. And i initialize memory with the generated data.