fixed point in verilog

hi. I understand that the fixed point in verilog is represented by signed [4:-2] where -2(2 bit for post binary point) is for tracking purpose. Pls correct me if i am wrong.

However, i have no idea on how to use in verilog for any arithmetic operation.

e.g.

module fixed_point_addition

(dataA, dataB, result_add, result_mult);

input signed [3:-1] dataA;

input signed [3:-1] dataB;

output signed [4:-2] result, result_mult;

assign result_add = dataA + dataB;

assign result_mult = dataA* dataB;

endmodule

In waveform editor, i cant set the value like 3.5. How to do this?

i set the input(dataA=0.5 and dataB=0.5) and output in fraction when performing simulation, the result(result_mult= 0.125). May i know the reason?

Can i have some simple source code in verilog(can perform 3.25 * -6.125) and how to perform the simulation?

Thanks