write a constraint for upper bit is equal to lower bit

 module test();

class packet;

rand bit {31:0] a;

constraint   c1 { foreach(a[i)

{

a[i]==a[31-i]}};}

endclass

packet p1=new();

initial begin

p1.randomize();

$display("the value is =%p", p1.a);

end

endmodule