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module mac (input clock, input reset, input enable, input clear,
input signed [15:0] x, input signed [15:0] y,
input [7:0] shift, output [15:0] z );
reg signed [30:0] product;
reg signed [39:0] z_int;
reg signed [15:0] z_shift;
reg enable_d1;
always @(posedge clock)
enable_d1 <= #1 enable;
always @(posedge clock)
if(reset | clear)
z_int <= #1 40'd0;
else if(enable_d1)
z_int <= #1 z_int + {{9{product[30]}},product};
always @(posedge clock)
product <= #1 x*y;
always @* // FIXME full case? parallel case?
case(shift)
//8'd0 : z_shift <= z_int[39:24];
//8'd1 : z_shift <= z_int[38:23];
//8'd2 : z_shift <= z_int[37:22];
//8'd3 : z_shift <= z_int[36:21];
//8'd4 : z_shift <= z_int[35:20];
//8'd5 : z_shift <= z_int[34:19];
8'd6 : z_shift <= z_int[33:18];
8'd7 : z_shift <= z_int[32:17];
8'd8 : z_shift <= z_int[31:16];
8'd9 : z_shift <= z_int[30:15];
8'd10 : z_shift <= z_int[29:14];
8'd11 : z_shift <= z_int[28:13];
//8'd12 : z_shift <= z_int[27:12];
//8'd13 : z_shift <= z_int[26:11];
//8'd14 : z_shift <= z_int[25:10];
//8'd15 : z_shift <= z_int[24:9];
//8'd16 : z_shift <= z_int[23:8];
//8'd17 : z_shift <= z_int[22:7];
//8'd18 : z_shift <= z_int[21:6];
//8'd19 : z_shift <= z_int[20:5];
//8'd20 : z_shift <= z_int[19:4];
//8'd21 : z_shift <= z_int[18:3];
//8'd22 : z_shift <= z_int[17:2];
//8'd23 : z_shift <= z_int[16:1];
//8'd24 : z_shift <= z_int[15:0];
default : z_shift <= z_int[15:0];
endcase // case(shift)
// FIXME do we need to saturate?
//assign z = z_shift;
assign z = z_int[15:0];
endmodule // mac
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