超前进位加法器求问

时间：10-02 整理：3721RD 点击：

超前进位加法器（没有cin），为什么这样设计结果有些正确有些错误?
module carry_adder(
input [8:1] x,
input [8:1] y,
output reg [8:1] s,
output reg carry_out
);
reg [4:0] i;
reg [8:1] p;
reg [8:1] G;
reg [8:0] c;
assign carry_out=c[8];
always @(*)
begin
      c[0]=0;
      for(i=1;i<=8;i=i+1)
         begin
            p=x^y;
            G=x&y;
            c=(p&c[i-1])|G;
            s=p^c;
         end
end
endmodule

仿真结果：
0X= 14 Y= 12 S= 14 carry_out=0
               50X=  1 Y=  8 S=  9 carry_out=0
               100X=  6 Y=  2 S=  2 carry_out=0
               150X=  5 Y= 19 S= 17 carry_out=0
               200X=  9 Y= 16 S= 25 carry_out=0
               250X=  0 Y= 17 S= 17 carry_out=0
               300X=  0 Y=  7 S=  7 carry_out=0
               350X= 19 Y=  0 S= 19 carry_out=0
               400X= 10 Y= 15 S= 11 carry_out=0
               450X= 15 Y=  6 S=  7 carry_out=0
               500X=  5 Y= 15 S=  5 carry_out=0
               550X= 18 Y=  6 S= 18 carry_out=0
               600X= 19 Y= 19 S= 19 carry_out=0
               650X= 11 Y=  8 S= 11 carry_out=0
               700X=  7 Y= 16 S= 23 carry_out=0
               750X= 19 Y=  1 S= 17 carry_out=0
               800X= 14 Y= 16 S= 30 carry_out=0
               850X= 15 Y= 12 S= 15 carry_out=0
               900X=  0 Y=  6 S=  6 carry_out=0
               950X= 19 Y=  0 S= 19 carry_out=0
$finish called from file "carry_outtb.v", line 41.
$finish at simulation time             1101000
         V C S S i m u l a t i o n R e p o r t
Time: 1101000 ps
CPU Time:    0.540 seconds;    Data structure size: 0.0Mb

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