一、无符号数
1.高位溢出赋给一个位宽不够的数
wire [3:0] a=4'b1111;//15
wire [3:0] b=4'b0010;//2
wire [3:0] c;
assign c = a + b;//17=10001
wire [3:0] a=4'b1111;
wire [3:0] b=4'b0010;
wire [2:0] c;
assign c = a + b;
高位截断,保留低位 ;
2.高位溢出赋给一个位宽足够的数
wire [3:0] a=4'b1111;
wire [3:0] b=4'b0010;
wire [4:0] c;
assign c = a + b;
结果正确;
3.对中间结果移位
wire [3:0] a=4'b1111;
wire [3:0] b=4'b0010;
wire [3:0] c;
assign c =(( a + b) >> 1); //17=10001
可以看出是先赋值再移位的;
wire [3:0] a=4'b1111;
wire [3:0] b=4'b0010;
wire [4:0] c;
assign c =(( a + b) >> 1); //17=10001
结果正确,左边补0;
wire [3:0] a=4'b1111;
wire [3:0] b=4'b0010;
wire [4:0] c;
assign c = ((a + b)>>>1) ;
>>>算数右移,无符号数还是补0;
二、有符号数
1.正常运算
wire signed [3:0] a=4'b1111;//-1
wire signed [3:0] b=4'b0010;//2
wire signed [3:0] c;
assign c =a + b;
wire signed [3:0] a=4'b1110;//-2
wire signed [3:0] b=4'b0001;//1
wire signed [3:0] c;
assign c =a + b;
2.赋给位宽不够的数
wire signed [3:0] a=4'b0111;//7
wire signed [3:0] b=4'b0010;//2
wire signed [3:0] c;
assign c =a + b; //9=01001
wire signed [3:0] a=4'b1001;//-7
wire signed [3:0] b=4'b1110;//-2
wire signed [3:0] c;
assign c =a + b;//-9=10111
舍弃高位 ;
3.赋给位宽足够的数
wire signed [3:0] a=4'b0111;
wire signed [3:0] b=4'b0010;
wire signed [4:0] c;
assign c =a + b;
4.给中间结果移位
wire signed [3:0] a=4'b1001;//-7
wire signed [3:0] b=4'b1110;//-2
wire signed [3:0] c;
assign c =(( a + b ) >> 1); //-9=10111
wire signed [3:0] a=4'b0111;//7
wire signed [3:0] b=4'b0010;//2
wire signed [3:0] c;
assign c =(( a + b ) >> 1);//9=01001
逻辑右移,高位都是都是补0;
wire signed [3:0] a=4'b1001;//-7
wire signed [3:0] b=4'b1110;//-2
wire signed [4:0] c;
assign c = ((a + b)>>>1) ;//-9=10111
>>>算数右移,截断赋值然后把最高位当符号位,补最高位 ;
总结:
>>逻辑右移,不管有符号还是无符号,都是补0;
>>>算术右移,补最高位;
三、有符号数与无符号数运算
1.只有两个操作数都是有符号数,才会把两个操作数都看作有符号数计算,否则无论是有符号数还是无符号数都会按照无符号数计算 ;
wire [3:0] a=4'b1001;
wire signed [3:0] b=4'b1110;
wire signed [4:0] c;
assign c = ((a + b)>>>1); //-9=10111
还是把c当做无符号数移位;
2.把a赋给b,若a是有符号数,则b高位用a的最高位填充,若a是无符号数,b的高位用0填充 ;
wire [3:0] a=4'b1001;
wire signed [3:0] b=4'b1001;
wire signed [4:0] c,d;
assign c=a;
assign d=b;