module fir(clk,x,y); input[7:0] x; input clk; output[15:0] y; reg[15:0] y; reg[7:0] tap0,tap1,tap2,tap3,tap4,tap5,tap6,tap7,tap8,tap9,tap10,tap11,tap12,tap13,tap14,tap15; reg[7:0] t0,t1,t2,t3,t4,t5,t6,t7; reg[15:0] sum;
always@(posedge clk)
begin
t0<=tap0+tap15;
t1<=tap1+tap14;
t2<=tap2+tap13;
t3<=tap3+tap12;
t4<=tap4+tap11;
t5<=tap5+tap10; t6<=tap6+tap9; t7<=tap7+tap8;
//利用对称性
sum<={t0[7],t0[7:1]}-{t0[7],t0[7],t0[7],t0[7],t0[7],t0[7:5]} -t1-{t1[7],t1[7:1]}-{t1[7],t1[7],t1[7],t1[7:3]} +(t2<<2)+t2+{t2[7],t2[7],t2[7:2]}+{t2[7],t2[7],t2[7],t2[7],t2[7:4]} +{t2[7],t2[7],t2[7],t2[7],t2[7],t2[7:5]} -{t3<<3}-(t3<<2)+t3-{t3[7],t3[7],t3[7:2]} +(t4<<4)+t4-{t4[7],t4[7],t4[7],t4[7:3]} -{t5<<7}+{(t5<<2)<<2}+(t5<<2)-{t5[7],t5[7:1]} -{t5[7],t5[7],t5[7:2]}-{t5[7],t5[7],t5[7],t5[7],t5[7:4]} +(t6<<7)+(t6<<3)-(t7<<7)-(t7<<6);
tap15<=tap14;tap14<=tap13;tap13<=tap12;tap12<=tap11; tap11<=tap10;tap10<=tap9;tap9<=tap8;tap8<=tap7; tap7<=tap6;tap6<=tap5;tap5<=tap4;tap4<=tap3; tap3<=tap2;tap2<=tap1;tap1<=tap0;tap0<=x; y<={sum[15],sum[15],sum[15],sum[15],sum[15],sum[15],sum[15],sum[15:7]}; end endmodule | 
