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[/] [ft816float/] [trunk/] [rtl/] [verilog2/] [BCDSubtract.sv] - Rev 78
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module BCDSubtract(clk, a, b, o, co);
parameter N=25;
input clk;
input [N*4-1:0] a;
input [N*4-1:0] b;
output reg [N*4-1:0] o;
output reg co;
wire [(N+1)*4-1:0] bc;
wire [(N+1)*4-1:0] o1, o2, o3;
wire c;
BCDNinesComplementN #(N+1) u1 (.i({4'h0,b}), .o(bc));
BCDAdd8NClk #(.N(N/2+1)) u2 (.clk(clk), .a({8'h00,a}), .b(bc), .o(o1), .ci(1'b0), .co(c));
BCDNinesComplementN #(N) u3 (.i(o1), .o(o2));
BCDAdd8NClk #(.N(N/2+1)) u4 (.clk(clk), .a(o1), .b({{N*8{1'b0}},1'b1}), .o(o3), .ci(1'b0), .co());
always_ff @(posedge clk)
if (c)
o <= o3;
else
o <= o2;
always_ff @(posedge clk)
co <= c;
endmodule
module BCDNinesComplement(i, o);
input [3:0] i;
output reg [3:0] o;
always_comb
case(i)
4'd0: o = 4'd9;
4'd1: o = 4'd8;
4'd2: o = 4'd7;
4'd3: o = 4'd6;
4'd4: o = 4'd5;
4'd5: o = 4'd4;
4'd6: o = 4'd3;
4'd7: o = 4'd2;
4'd8: o = 4'd1;
4'd9: o = 4'd0;
4'd10: o = 4'd9;
4'd11: o = 4'd8;
4'd12: o = 4'd7;
4'd13: o = 4'd6;
4'd14: o = 4'd5;
4'd15: o = 4'd4;
endcase
endmodule
module BCDNinesComplementN(i, o);
parameter N=25;
input [N*4-1:0] i;
output [N*4-1:0] o;
genvar g;
generate begin : gNC
for (g = 0; g < N; g = g + 1)
BCDNinesComplement utc1 (i[g*4+3:g*4],o[g*4+3:g*4]);
end
endgenerate
endmodule
module BCDTensComplement(i, o);
input [3:0] i;
output reg [3:0] o;
always_comb
case(i)
4'd0: o = 4'd0;
4'd1: o = 4'd9;
4'd2: o = 4'd8;
4'd3: o = 4'd7;
4'd4: o = 4'd6;
4'd5: o = 4'd5;
4'd6: o = 4'd4;
4'd7: o = 4'd3;
4'd8: o = 4'd2;
4'd9: o = 4'd1;
4'd10: o = 4'd0;
4'd11: o = 4'd9;
4'd12: o = 4'd8;
4'd13: o = 4'd7;
4'd14: o = 4'd6;
4'd15: o = 4'd5;
endcase
endmodule
module BCDTensComplementN(i, o);
parameter N=25;
input [N*4-1:0] i;
output [N*4-1:0] o;
genvar g;
generate begin : gTC
for (g = 0; g < N; g = g + 1)
BCDTensComplement utc1 (i[g*4+3:g*4],o[g*4+3:g*4]);
end
endgenerate
endmodule
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