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diff --git a/tests/xilinx/macc.v b/tests/xilinx/macc.v
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+// Signed 40-bit streaming accumulator with 16-bit inputs
+// File: HDL_Coding_Techniques/multipliers/multipliers4.v
+//
+// Source:
+// https://www.xilinx.com/support/documentation/sw_manuals/xilinx2014_2/ug901-vivado-synthesis.pdf p.90
+//
+module macc # (parameter SIZEIN = 16, SIZEOUT = 40) (
+	input clk, ce, sload,
+	input signed [SIZEIN-1:0] a, b,
+	output signed [SIZEOUT-1:0] accum_out
+);
+// Declare registers for intermediate values
+reg signed [SIZEIN-1:0] a_reg, b_reg;
+reg sload_reg;
+reg signed [2*SIZEIN-1:0] mult_reg;
+reg signed [SIZEOUT-1:0] adder_out, old_result;
+always @* /*(adder_out or sload_reg)*/ begin // Modification necessary to fix sim/synth mismatch
+	if (sload_reg)
+		old_result <= 0;
+	else
+		// 'sload' is now active (=low) and opens the accumulation loop.
+		// The accumulator takes the next multiplier output in
+		// the same cycle.
+		old_result <= adder_out;
+end
+
+always @(posedge clk)
+	if (ce)
+	begin
+		a_reg <= a;
+		b_reg <= b;
+		mult_reg <= a_reg * b_reg;
+		sload_reg <= sload;
+		// Store accumulation result into a register
+		adder_out <= old_result + mult_reg;
+	end
+
+	// Output accumulation result
+	assign accum_out = adder_out;
+
+endmodule