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diff --git a/techlibs/xilinx/mux_map.v b/techlibs/xilinx/mux_map.v
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+++ b/techlibs/xilinx/mux_map.v
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+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *                2019  Eddie Hung    <eddie@fpgeh.com>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+module \$shiftx (A, B, Y);
+  parameter A_SIGNED = 0;
+  parameter B_SIGNED = 0;
+  parameter A_WIDTH = 1;
+  parameter B_WIDTH = 1;
+  parameter Y_WIDTH = 1;
+
+  input [A_WIDTH-1:0] A;
+  input [B_WIDTH-1:0] B;
+  output [Y_WIDTH-1:0] Y;
+
+  parameter [B_WIDTH-1:0] _TECHMAP_CONSTMSK_B_ = 0;
+  parameter [B_WIDTH-1:0] _TECHMAP_CONSTVAL_B_ = 0;
+
+  generate
+    genvar i, j;
+    // TODO: Check if this opt still necessary
+    if (B_SIGNED) begin
+      if (_TECHMAP_CONSTMSK_B_[B_WIDTH-1] && _TECHMAP_CONSTVAL_B_[B_WIDTH-1] == 1'b0)
+        // Optimisation to remove B_SIGNED if sign bit of B is constant-0
+        \$__XILINX_MUX_  #(.A_SIGNED(A_SIGNED), .B_SIGNED(0), .A_WIDTH(A_WIDTH), .B_WIDTH(B_WIDTH-1'd1), .Y_WIDTH(Y_WIDTH)) _TECHMAP_REPLACE_ (.A(A), .B(B[B_WIDTH-2:0]), .Y(Y));
+      else
+        wire _TECHMAP_FAIL_ = 1;
+    end
+    else if (B_WIDTH < 3 || A_WIDTH <= 4) begin
+      wire _TECHMAP_FAIL_ = 1;
+    end
+    else begin
+        \$__XILINX_MUX_  #(.A_SIGNED(A_SIGNED), .B_SIGNED(B_SIGNED), .A_WIDTH(A_WIDTH), .B_WIDTH(B_WIDTH), .Y_WIDTH(Y_WIDTH)) _TECHMAP_REPLACE_ (.A(A), .B(B), .Y(Y));
+    end
+  endgenerate
+endmodule