module mrl(a,b,res,rs);
input [3:0]a;
input [3:0]b;
output [5:0]res;
output rs;
reg overflow;
reg [2:0]r;
reg [1:0]sum;
reg [2:0]cb;
reg [1:0]carry;
integer ii;
always @(a[1] || a[2] || a[3] || a[0] || b[0] ||b[1]||b[2]||b[3])
begin
sum[0]=1'b1;
sum[1]=1'b1;
end
always @(*)
begin
cb[0]=b[0];
cb[1]=b[1];
cb[2]=b[2];
for(ii=0; ii<3; ii=ii+1)
begin
if(cb[0]==1'b1)
begin
r[0] = a[0]^r[0]^~cb[0];
carry[0] = (a[0]&r[0])|(r[0]&~cb[0])|(~cb[0]&a[0]);
r[1] = a[1]^r[1]^carry[0];
carry[1] = (a[1]&r[1])|(r[1]&carry[0])|(carry[0]&a[1]);
r[2] = a[2]^r[2]^carry[1];
overflow = (a[2]&r[2])|(r[2]&carry[1])|(carry[1]&a[2]);
end
cb[2]=cb[1];
cb[1]=cb[0];
cb[0]=r[2];
r[2]=r[1];
r[1]=r[0];
r[0]=overflow;
overflow=1'b0;
end
end
assign rs=a[3]^b[3];
assign res[0]=r[0];
assign res[1]=r[1];
assign res[2]=r[2];
assign res[3]=cb[0];
assign res[4]=cb[1];
assign res[5]=cb[2];
endmodule
