How to Randomize a Real Variable?

Hi Everyone !!!,

    In This session we are going to see how to Randomize a Real variable.

  Using randomize() method we can able to randomize only integral data-type variables only(bit,logic,reg,wire,integer,enum, packed struct). 

    Here I show the two ways to randomize variable of type real.

Example 1:

In below mentioned code I am trying to randomize real data types,It leads to compilation error. LRM won't support real and string data_types for Randomization.

class rand_rdata;

  rand real rdata;

endclass

module TB;

  rand_rdata r;

  initial begin

    r=new();

    r.randomize();

    repeat(5) begin

      $display(" REAL DATA %0d ",r.rdata);

    end

  end

endmodule

OUTPUT:

TimeScale is 1 ns / 1 ns

Error-[IRRVD] Illegal rand variable type
testbench.sv, 16
"rdata"
The rand variable 'rdata' must be an integral type, an enum type, a packed
struct, or of type 'bit'.
Change the type of the random variable 'rdata' to an integral, bit, packed
struct, or enum type or remove the 'rand' qualifier.

1 error

$bitstoreal converts the bit value to a real number. By using this system function real values can be generated.  Real value randomization Logic's are explained in Example 2&3.

Example 2:

class rand_real;

  rand bit [63:0] data;

  real rdata;

  function void post_randomize();

    this.rdata = $bitstoreal(data);  // This is the trick here. (Randomized data value is converted to Real value by using system function)

  endfunction

endclass

module top();

  rand_real R;

  initial begin

    R = new();

    repeat (4) begin

      if (R.randomize()) begin

        $display ("R.data=%0d, R.rdata=%e", R.data, R.rdata);

      end

      else begin

      $error ("Randomization Failed");

      end

    end

  end

endmodule

OUTPUT:

R.data=11603960314292000697, R.rdata=-1.560983e-149
R.data=5297240865832474715, R.rdata=1.397281e+46
R.data=17254093185709081402, R.rdata=-7.145857e+228
R.data=12279536430588681223, R.rdata=-2.239116e-104
V C S S i m u l a t i o n R e p o r t

Example 3:

class rand_real;

  rand integer i, j;

  real rdata;

  function void post_randomize();

    this.rdata = $bitstoreal({i, j}); //This is the trick here (Randomized i,j converted to equivalent real here)

  endfunction

endclass

module TB();

  rand_real R;

  initial begin

    R = new(); 

    repeat (5) begin

      if (R.randomize()) begin

        $display ("R.i=%0d, R.j=%0d, R.real_data=%e", R.i, R.j, R.rdata);

      end

      else begin

      $error ("Randomization Failed");

      end

    end

  end

endmodule

OUTPUT:

R.i=-384116807, R.j=-1593209748, R.real_data=-2.006518e+198
R.i=1637914715, R.j=1233360000, R.real_data=1.866503e+162
R.i=397247290, R.j=-277685674, R.real_data=1.263399e-194
R.i=-407577593, R.j=-1435914926, R.real_data=-3.717586e+191
R.i=-1298805792, R.j=-1452694196, R.real_data=-5.174229e-65
V C S S i m u l a t i o n R e p o r t

Hope this logic's will be useful to everyone !!!

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