$lcu

$lcu (P, G, CI, CO)

Lookahead carry unit A building block dedicated to fast computation of carry-bits used in binary arithmetic operations. By replacing the ripple carry structure used in full-adder blocks, the more significant bits of the sum can be expected to be computed more quickly. Typically created during techmap of $alu cells (see the “_90_alu” rule in +/techmap.v). Simulation model (Verilog) ————————–

Listing 304 simlib.v:554

module \$lcu (P, G, CI, CO);

    parameter WIDTH = 1;

    input [WIDTH-1:0] P;    // Propagate
    input [WIDTH-1:0] G;    // Generate
    input CI;               // Carry-in

    output reg [WIDTH-1:0] CO; // Carry-out

    integer i;
    always @* begin
        CO = 'bx;
        if (^{P, G, CI} !== 1'bx) begin
            CO[0] = G[0] || (P[0] && CI);
            for (i = 1; i < WIDTH; i = i+1)
                CO[i] = G[i] || (P[i] && CO[i-1]);
        end
    end

endmodule

Note

This page was auto-generated from the output of help $lcu.