无符号数运算，左值位宽不够，发生截断的现象 reg [3:0] a = 4'b1111;//15reg [3:0] b = 4'b0010;//2wire [3:0] c;wire [3:0] show_c;//17 10001assign c = a + b;//1assign show_c = a + b;//1
2. 两个无符号数运算，赋值给一个有符号的数。可以看出，右侧先按照无符号数进行运算，取得的运算结果按照左侧的符号进行数据显示。
reg [3:0] a = 15;//4'b1111reg [3:0] b = 2;//4'b0010reg signed [3:0] c;reg signed [4:0] d;reg signed [4:0] e; initial beginc = a + b;d = a + b;e = b - a;//17 10001 $display("c = %d",c); //1 0001$display("d = %d",d); //-15 10001$display("e = %d",e); //-13 10011 end
3. 两个无符号数运算，无符号数赋负值（补码）。按照该补码对应的正值进行处理。结果同上。
reg [3:0] a = -1;//4'b1111 15reg [3:0] b = 2 ;//4'b0010wire signed [3:0] c;wire signed [3:0] show_c;wire signed [4:0] d;wire signed [4:0] show_d;//17 10001 assign c = a + b;//0001assign show_c = a + b;//1assign d = a + b;//10001assign show_d = a + b; //-15 signed
4. 有符号数和无符号数运算，赋值给有符号数。补码进行运算，如果左值位宽不够，进行截位，取得的结果为：3（4’b0011）。位宽足够，取得结果为-13（10011）。
reg signed [4:0] a = -15;//5'b10001reg [3:0] b = 2;//4'b0010wire signed [3:0] c;wire signed [3:0] show_c;wire signed [4:0] d;wire signed [4:0] show_d; assign c = a + b;//0011assign show_c = a + b;//3assign d = a + b;//10011assign show_d = a + b; //-13
5. 有符号数和无符号数的比较
一个无符号数和一个有符号数比较，都视为无符号数，按照各自补码的大小进行比较；
reg [3:0] a = 15;//4'b1111reg [3:0] b = 14;//4'b1110reg signed [3:0] c =-1 ;//4'b1111reg signed [4:0] d =-2; //5'b11110 initial beginif(a <= c) begin $display("a <= c");//成立endif(b <= c) begin $display("b <= c");//成立endif(c > d) begin $display("c > d");//成立end end
6. 两个无符号数已经进行移位。数据先按照左值进行截断，然后再进行移位。算数右移时，不管左值是否有符号，都按照无符号数进行补零操作。
reg [3:0] a = 15;//4'b1111reg [3:0] b = 4;//4'b0100reg [3:0] c ;reg signed [3:0] d ;reg signed [4:0] e ; reg signed [4:0] f; initial beginc = ( a + b ) >> 1;d = ( a + b ) >> 1;e = ( a + b ) >> 1;f = ( a + b ) >>> 1;$display("c = %d",c);//1 0001$display("d = %d",d);//1 0001$display("e = %d",e);//9 1001$display("f = %d",f);//9 1001
7.有符号数进行移位。只有参与运算的两个数都是有符号数，才按照有符号数进行算数右移，补最高位。不然，就补0.
reg signed [3:0] a = -7;//4'b1001reg [3:0] b = 4;//4'b0100reg signed [3:0] c = 4;//4'b0100reg signed [3:0] d ;reg signed [3:0] e ; reg signed [3:0] f; initial begind = ( a + b ) >> 1;//a + b =-3 1101e = ( a + b ) >>> 1;f = ( a + c ) >>> 1;$display("d = %d",d);//6 0110$display("e = %d",e);//6 0110$display("f = %d",f);//-2 1110