大于/小于对fmax的影响

module A_prj
    (
    clk,
    D,
 E,
    x,
    y,
    m,
    n,
    z
    );

input clk;
input [31:0] D, E;
input [31:0] x, y;
input [31:0] m, n;

output [31:0] z;

reg   P, L;
reg  [31:0] D_in, E_in;
reg  [31:0] x_in, y_in;
reg  [31:0] m_in, n_in;
reg  [31:0] s, v;
reg  [31:0] z;

always @(posedge clk)
begin
    D_in <= D;
    E_in <= E;
    x_in <= x;
    y_in <= y;
    m_in <= m;
    n_in <= n;
end

/*
//slow
always @(posedge clk)
    if (D_in >= E_in)
        s <= x_in + y_in;
    else
        s <= x_in - y_in;
always @(posedge clk)
 if (D_in >= E_in)
        v <= m_in + n_in;
    else
        v <= m_in - n_in;
*/
/*
//normal
always @(posedge clk)
    if (D_in >= E_in)
        P <= 1'b1;
    else
        P <= 1'b0;
always @(posedge clk)
 if (P)
        s <= x_in + y_in;
    else
        s <= x_in - y_in;
always @(posedge clk)
 if (P)
        v <= m_in + n_in;
    else
        v <= m_in - n_in;
*/

//fast
always @(posedge clk)
    if (D_in >= E_in)
        P <= 1'b1;
    else
        P <= 1'b0;
always @(posedge clk)
    if (D_in >= E_in)
        L <= 1'b1;
    else
        L <= 1'b0;
always @(posedge clk)
 if (P)
        s <= x_in + y_in;
    else
        s <= x_in - y_in;
always @(posedge clk)
 if (L)
        v <= m_in + n_in;
    else
        v <= m_in - n_in;

always @(posedge clk)
 z <= s + v;

endmodule