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module fourbyfour_sad_tb ();

wire [7:0] x0,x1,x2,x3,x4,x5,x6,x7,x8,x9,xa,xb,xc,xd,xe,xf;
wire [7:0] y0,y1,y2,y3,y4,y5,y6,y7,y8,y9,ya,yb,yc,yd,ye,yf;

reg [8*16*2-1:0] data;
reg fail;

assign {x0,x1,x2,x3,x4,x5,x6,x7,x8,x9,xa,xb,xc,xd,xe,xf,
		y0,y1,y2,y3,y4,y5,y6,y7,y8,y9,ya,yb,yc,yd,ye,yf} = data;

wire [11:0] sad;

fourbyfour_sad fs (
	x0,x1,x2,x3,x4,x5,x6,x7,x8,x9,xa,xb,xc,xd,xe,xf,
	y0,y1,y2,y3,y4,y5,y6,y7,y8,y9,ya,yb,yc,yd,ye,yf,
	sad
);

// compute correct answer using entirely different method
wire [12:0] diff[15:0];

genvar i;
generate 	
	for (i = 0; i<16; i = i+1)
	begin : check
		wire [12:0] j,k;
		assign j = data[i*8+7:i*8];
		assign k = data[8*16+i*8+7:8*16+i*8];
		assign diff[i] = (j > k) ? j - k : k - j;
	end
endgenerate

integer q, cume; 

always begin 
	#100 cume = 0; 
	for (q = 0; q<16; q=q+1) 
	begin : sum
		cume = cume + diff[q];
	end
end

initial begin 
	data = 0;
	fail = 0;
	#1000000
	if (!fail) $display ("PASS");
	$stop;
end

// stim generate and check
always begin
	#1000 data = {$random,$random,$random,$random,
					$random,$random,$random,$random};
	#1000 if (cume != sad) begin
		$display ("Mismatch at time %d",$time);
		fail = 1;
	end
end

endmodule