
A priority encoder is a combinational circuit that, when given an input
bit vector, outputs the position of the first 1 bit in the vector. For
example, a 8-bit priority encoder given the input 8'b10010000 would
output 3'd4, because bit[4] is first bit that is high. Build a 4-bit
priority encoder. For this problem, if none of the input bits are high
(i.e., input is zero), output zero. Note that a 4-bit number has 16
possible combinations.

module TopModule (
  input [3:0] in,
  output reg [1:0] pos
);

