[Practice]运算器

加减乘除

与或非、异或

`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Company: 
// Engineer: 
// 
// Create Date:    14:09:07 06/12/2014 
// Design Name: 
// Module Name:    t 
// Project Name: 
// Target Devices: 
// Tool versions: 
// Description: 
//
// Dependencies: 
//
// Revision: 
// Revision 0.01 - File Created
// Additional Comments: 
//
//////////////////////////////////////////////////////////////////////////////////

module t(
input wire [3:0] a,
input wire [3:0] b,
input wire [3:0] state,
output reg [7:0] result
    );

reg [3:0] quotient;
integer j;
reg [3:0] remainder;
reg [3:0] saved_b;

always @(state)
	case (state)
		//add
		8: result = a + b;
		
		//sub
		4: begin
			result = (a > b) ? (a-b) : (b-a);
			if (a < b)
				result[7] = 1;
			end
			
		//multiple
		2: result = a * b;
		
		//div
		1: begin
				remainder = a;
				saved_b = b;
				quotient = 8'b00000000;
				if (b == 0)
					result = 8'b11111111;
				else
					begin
						for (j = 0; j < 16; j = j+1)
						if (remainder >= saved_b)
							begin
								remainder = remainder - saved_b;
								quotient = quotient + 1;
							end
						result = remainder;
						result[7] = quotient[3];
						result[6] = quotient[2];
						result[5] = quotient[1];
						result[4] = quotient[0];
					end
			end
		
		//and
		12: result = a & b;
		
		//or
		6: result = a | b;
	
		//not
		3: begin
			result = ~b;
			result[7] = !a[3];
			result[6] = !a[2];
			result[5] = !a[1];
			result[4] = !a[0];
			end
			
		//xor
		9: result = a ^ b;
		
	endcase
endmodule