关于有符号数据类型的示例

我们学习一下Systemverilog中的有符号数据类型的赋值。

 

module top;
 logic [7:0] r1;
 logic signed [7:0] sr1;
 initial begin
    r1 = -2;
    $display($stime,,,"r1=%d",r1);
    sr1 = -2;
    $display($stime,,,"sr1=%d",sr1);
    r1 = r1+1;
    $display($stime,,,"r1=%d",r1);
    sr1 = sr1+1;
    $display($stime,,,"sr1=%d",sr1);
 end
 endmodule

 

Simulation log:

 

# run –all
# 0 r1=254

# 0 sr1= -2
# 0 r1=255
# 0 sr1= -1
# exit

 

" r1 "被声明为默认的无符号8位向量，而" sr1 "被声明为有符号8位向量。

当我们赋值r1 =−2时，因为“r1”是无符号的，所以它实际上会拿到值254(相当于十进制数字−2)。但是“sr1”会拿到值−2。

当我们给“r1”加一个1时，它的计算结果是255(254 + 1)。当我们给“sr1”加一个1时，它的计算结果是- 1(−2 + 1)。

默认情况下，logic, reg, wire,input,output都是无符号的，但是也可以声明为signed:

 

wire signed [7:0] w;
module sm (input signed [7:0] iBus, output logic signed 
[7:0] oBus);

 

下面还有一些简单的示例：

 

logic signed [3:0] sr = -1; ( sr = 4’sb1111)
logic signed [7:0] sr1 = 1; (sr1 = 8’sb00000001)
logic [7:0] adds = sr + sr1; ( adds = 8’b00000000)

logic [7:0] usr = 1;
logic signed [7:0] s_add;
s_add = sr + usr; (s_add = 15+1 = 8’sb00010000) (signed + 
unsigned = unsigned; sr is treated as unsigned 15)

 

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