VHDL: use the length of an integer generic to determine number of select lines

Question

I\'m trying to create a reusable barrel shifter; it takes an input array of bits and shifts them a certain number of positions (determined by another input). I want to parameter

Answer 1

You can use the math library to calculate log2 and ceil of the logarit result to declare the size of SHIFT_CNT.

use IEEE.math_real.all;

or specific functions

use IEEE.math_real."ceil";
use IEEE.math_real."log2";

For example you want to calculate clog2 of value a

result := integer(ceil(log2(real(a))));

If you just use these function to calculate paramater, your code is synthesizable (I did it).

If you don't want use it in entities, you can declare them in a library or generic with these functions.