Added files into modelsim folder

ModelSim/shifter.sv

@@ -1,9 +1,9 @@
 `ifndef SHIFTER_H_SV
 `define SHIFTER_H_SV
 module shifter #(width=2)(input logic [2:0] op,
-    input logic[2**width-1:0] A, input logic[2**width-1:0] B, input logic[width-1:0] C,
+    input logic[2**width-1:0] A, input logic[2**width-1:0] B, input logic[width-1:0] C, 
     output logic[2**width-1:0] OUT_1);
-
+// A and B are 2^n bits wide and C is n bits wide as according to the docs
     always_comb begin
         case (op)
             3'b000: OUT_1 = A << C;
@@ -16,4 +16,4 @@ module shifter #(width=2)(input logic [2:0] op,
         endcase
     end    
 endmodule
-`endif
+`endif