From 7977574995baa2cdba1401233179f9f84fe96a3a Mon Sep 17 00:00:00 2001
From: Eddie Hung <eddie@fpgeh.com>
Date: Thu, 16 Jan 2020 15:25:49 -0800
Subject: New techmap +/shiftx2mux.v which decomposes LSB first; better for ABC

---
 techlibs/common/Makefile.inc |  1 +
 techlibs/common/shiftx2mux.v | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 techlibs/common/shiftx2mux.v

(limited to 'techlibs/common')

diff --git a/techlibs/common/Makefile.inc b/techlibs/common/Makefile.inc
index a42f63128..5d797ec1d 100644
--- a/techlibs/common/Makefile.inc
+++ b/techlibs/common/Makefile.inc
@@ -30,3 +30,4 @@ $(eval $(call add_share_file,share,techlibs/common/cmp2lut.v))
 $(eval $(call add_share_file,share,techlibs/common/cells.lib))
 $(eval $(call add_share_file,share,techlibs/common/mul2dsp.v))
 $(eval $(call add_share_file,share,techlibs/common/dummy.box))
+$(eval $(call add_share_file,share,techlibs/common/shiftx2mux.v))
diff --git a/techlibs/common/shiftx2mux.v b/techlibs/common/shiftx2mux.v
new file mode 100644
index 000000000..5366d6749
--- /dev/null
+++ b/techlibs/common/shiftx2mux.v
@@ -0,0 +1,38 @@
+(* techmap_celltype = /*"$shift*/ "$shiftx" *)
+module _80_shift_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;
+        localparam CLOG2_Y_WIDTH = $clog2(Y_WIDTH);
+
+        if (B_WIDTH <= CLOG2_Y_WIDTH+1)
+            wire _TECHMAP_FAIL_ = 1;
+        // In order to perform this optimisation, this $shiftx must
+        //   only shift in units of Y_WIDTH, which we check by ensuring
+        //   that the appropriate LSBs of B are zero
+        else if (_TECHMAP_CONSTMSK_B_[CLOG2_Y_WIDTH-1:0] == {CLOG2_Y_WIDTH{1'b1}} && _TECHMAP_CONSTVAL_B_[CLOG2_Y_WIDTH-1:0] != {CLOG2_Y_WIDTH{1'b0}})
+            wire _TECHMAP_FAIL_ = 1;
+        else begin
+            // Halve the size of $shiftx by $mux-ing A according to 
+            //   the LSB of B, after discarding the zeroed bits
+            wire [(A_WIDTH+Y_WIDTH)/2-1:0] AA;
+            for (i = 0; i < (A_WIDTH/Y_WIDTH); i=i+2)
+                assign AA[(i/2)*Y_WIDTH +: Y_WIDTH] = B[CLOG2_Y_WIDTH] ? A[(i+1)*Y_WIDTH +: Y_WIDTH] : A[(i+0)*Y_WIDTH +: Y_WIDTH];
+            $shiftx #(.A_SIGNED(A_SIGNED), .B_SIGNED(B_SIGNED), .A_WIDTH((A_WIDTH+Y_WIDTH)/2'd2), .B_WIDTH(B_WIDTH-1), .Y_WIDTH(Y_WIDTH)) _TECHMAP_REPLACE_ (.A(AA), .B({B[B_WIDTH-1:CLOG2_Y_WIDTH+1], {CLOG2_Y_WIDTH{1'b0}}}), .Y(Y));
+        end
+    endgenerate
+endmodule
+
+
-- 
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