From 6c78bd36372b0f38ea18cacf60996778448fe48e Mon Sep 17 00:00:00 2001
From: "Emil J. Tywoniak" <emil@tywoniak.eu>
Date: Thu, 28 Nov 2024 15:13:51 +0100
Subject: [PATCH] techmap: add a Han-Carlson option for `$lcu` mapping

---
 techlibs/common/Makefile.inc          |  1 +
 techlibs/common/choices/han-carlson.v | 57 +++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)
 create mode 100644 techlibs/common/choices/han-carlson.v

diff --git a/techlibs/common/Makefile.inc b/techlibs/common/Makefile.inc
index fa5c2a825..cb67d6329 100644
--- a/techlibs/common/Makefile.inc
+++ b/techlibs/common/Makefile.inc
@@ -36,3 +36,4 @@ $(eval $(call add_share_file,share,techlibs/common/abc9_unmap.v))
 $(eval $(call add_share_file,share,techlibs/common/cmp2lcu.v))
 $(eval $(call add_share_file,share,techlibs/common/cmp2softlogic.v))
 $(eval $(call add_share_file,share/choices,techlibs/common/choices/kogge-stone.v))
+$(eval $(call add_share_file,share/choices,techlibs/common/choices/han-carlson.v))
diff --git a/techlibs/common/choices/han-carlson.v b/techlibs/common/choices/han-carlson.v
new file mode 100644
index 000000000..4c93c6f7e
--- /dev/null
+++ b/techlibs/common/choices/han-carlson.v
@@ -0,0 +1,57 @@
+(* techmap_celltype = "$lcu" *)
+module _85_lcu_han_carlson (P, G, CI, CO);
+	parameter WIDTH = 2;
+
+	(* force_downto *)
+	input [WIDTH-1:0] P, G;
+	input CI;
+
+	(* force_downto *)
+	output [WIDTH-1:0] CO;
+
+	integer i, j;
+	(* force_downto *)
+	reg [WIDTH-1:0] p, g;
+
+	always @* begin
+		i = 0;
+		p = P;
+		g = G;
+
+		// in almost all cases CI will be constant zero
+		g[0] = g[0] | (p[0] & CI);
+		if (i < $clog2(WIDTH)) begin
+
+			// First layer: BK
+			for (j = WIDTH - 1; j >= 0; j = j - 1) begin
+				if (j % 2 == 1) begin
+					g[j] = g[j] | p[j] & g[j - 1];
+					p[j] = p[j] & p[j - 1];
+				end
+			end
+
+			// Inner (log(WIDTH) - 1) layers: KS
+			for (i = 1; i < $clog2(WIDTH); i = i + 1) begin
+				for (j = WIDTH - 1; j >= 2**i; j = j - 1) begin
+					if (j % 2 == 1) begin
+						g[j] = g[j] | p[j] & g[j - 2**i];
+						p[j] = p[j] & p[j - 2**i];
+					end
+				end
+			end
+
+			// Last layer: BK
+			if (i < ($clog2(WIDTH) + 1)) begin
+				for (j = WIDTH - 1; j >= 0; j = j - 1) begin
+					if ((j % 2 == 0) && (j > 0)) begin
+						g[j] = g[j] | p[j] & g[j - 1];
+						p[j] = p[j] & p[j - 1];
+					end
+				end
+			end
+
+		end
+	end
+
+	assign CO = g;
+endmodule