4-Bit Full Adder Circuit Implementation in Verilog

This\ module\ implements\ a\ 4-bit\ full\ adder\ circuit.\ The\ inputs\ A,\ B,\ and\ C\ are\ the\ three\ bits\ to\ be\ added,\ and\ the\ outputs\ S,\ S1,\ S2,\ S3,\ and\ Ci\ represent\ the\ sum\ and\ carry-out\ bits.\ \n\ \nThe\ sum\ bit\ S\ is\ calculated\ by\ first\ performing\ an\ XOR\ operation\ between\ A\ and\ B,\ and\ then\ XORing\ the\ result\ with\ C.\ This\ is\ represented\ by\ the\ line\ xor(S,S1,C). \ \n\ \nThe\ carry-out\ bit\ Ci\ is\ calculated\ by\ first\ performing\ an\ AND\ operation\ between\ A\ and\ B,\ and\ then\ ORing\ the\ result\ with\ the\ AND\ operation\ between\ S1\ and\ C.\ This\ is\ represented\ by\ the\ line\ or(Ci,S2,S3). \ \n\ \nThe\ intermediate\ wires\ S1,\ S2,\ and\ S3\ are\ used\ to\ store\ the\ results\ of\ the\ XOR\ and\ AND\ operations\ for\ later\ use\ in\ calculating\ S\ and\ Ci.\ \n\ \nNote:\ There\ are\ two\ possible\ implementations\ for\ the\ sum\ and\ carry-out\ calculations.\ The\ commented\ lines\ represent\ an\ alternative\ implementation.