i am trying to realize RSA algorithm in verilog but when i tried to use the divide and modulus operations for modular exponentiation . XST is giving error that "Can not simplify operator DIV." please help me with this error.

Hi dahiya,

what is the divisor of your algorithm? If it is a power of 2, then "a div 2^n"
essentially means "shift a right by n bits", and "a mod 2^n" means "use the
n least significant bits of a", so that no actual division is necessary (which
is difficult to implement automatically with tools because pure combinational
logic is out of the question for general divisors).

Hellwig