4 files changed, 90 insertions, 0 deletions

diff --git a/kernel/celltypes.h b/kernel/celltypes.h
index 74e9f1fd5..b42cf4e9a 100644
--- a/kernel/celltypes.h
+++ b/kernel/celltypes.h
@@ -106,6 +106,7 @@ struct CellTypes
 			setup_type(type, {"\\A", "\\B", "\\S"}, {"\\Y"}, true);
 
 		setup_type("$alu", {"\\A", "\\B", "\\CI", "\\BI"}, {"\\X", "\\Y", "\\CO"}, true);
+		setup_type("$fa", {"\\A", "\\B", "\\C"}, {"\\X", "\\Y"}, true);
 
 		setup_type("$assert", {"\\A", "\\EN"}, std::set<RTLIL::IdString>(), true);
 	}
diff --git a/kernel/consteval.h b/kernel/consteval.h
index f995c9cc2..7423f950f 100644
--- a/kernel/consteval.h
+++ b/kernel/consteval.h
@@ -155,6 +155,31 @@ struct ConstEval
 			else
 				set(sig_y, y_values.front());
 		}
+		else if (cell->type == "$fa")
+		{
+			RTLIL::SigSpec sig_c = cell->getPort("\\C");
+			RTLIL::SigSpec sig_x = cell->getPort("\\X");
+			int width = SIZE(sig_c);
+
+			if (!eval(sig_a, undef, cell))
+				return false;
+
+			if (!eval(sig_b, undef, cell))
+				return false;
+
+			if (!eval(sig_c, undef, cell))
+				return false;
+
+			RTLIL::Const t1 = const_xor(sig_a.as_const(), sig_b.as_const(), false, false, width);
+			RTLIL::Const val_y = const_xor(t1, sig_c.as_const(), false, false, width);
+
+			RTLIL::Const t2 = const_and(sig_a.as_const(), sig_b.as_const(), false, false, width);
+			RTLIL::Const t3 = const_and(sig_c.as_const(), t1, false, false, width);
+			RTLIL::Const val_x = const_or(t2, t3, false, false, width);
+
+			set(sig_y, val_y);
+			set(sig_x, val_x);
+		}
 		else if (cell->type == "$alu")
 		{
 			bool signed_a = cell->parameters.count("\\A_SIGNED") > 0 && cell->parameters["\\A_SIGNED"].as_bool();
diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index 97a2946a6..b5cede8b2 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -620,6 +620,16 @@ namespace {
 				return;
 			}
 
+			if (cell->type == "$fa") {
+				port("\\A", param("\\WIDTH"));
+				port("\\B", param("\\WIDTH"));
+				port("\\C", param("\\WIDTH"));
+				port("\\X", param("\\WIDTH"));
+				port("\\Y", param("\\WIDTH"));
+				check_expected();
+				return;
+			}
+
 			if (cell->type == "$alu") {
 				param_bool("\\A_SIGNED");
 				param_bool("\\B_SIGNED");
@@ -1793,6 +1803,11 @@ void RTLIL::Cell::fixup_parameters(bool set_a_signed, bool set_b_signed)
 		return;
 	}
 
+	if (type == "$fa") {
+		parameters["\\WIDTH"] = SIZE(connections_["\\Y"]);
+		return;
+	}
+
 	bool signedness_ab = !type.in("$slice", "$concat", "$macc");
 
 	if (connections_.count("\\A")) {
diff --git a/kernel/satgen.h b/kernel/satgen.h
index 3429f8239..4aabe4378 100644
--- a/kernel/satgen.h
+++ b/kernel/satgen.h
@@ -963,6 +963,55 @@ struct SatGen
 			return true;
 		}
 
+		if (cell->type == "$fa")
+		{
+			std::vector<int> a = importDefSigSpec(cell->getPort("\\A"), timestep);
+			std::vector<int> b = importDefSigSpec(cell->getPort("\\B"), timestep);
+			std::vector<int> c = importDefSigSpec(cell->getPort("\\C"), timestep);
+			std::vector<int> y = importDefSigSpec(cell->getPort("\\Y"), timestep);
+			std::vector<int> x = importDefSigSpec(cell->getPort("\\X"), timestep);
+
+			std::vector<int> yy = model_undef ? ez->vec_var(y.size()) : y;
+			std::vector<int> xx = model_undef ? ez->vec_var(x.size()) : x;
+
+			std::vector<int> t1 = ez->vec_xor(a, b);
+			ez->assume(ez->vec_eq(yy, ez->vec_xor(t1, c)));
+
+			std::vector<int> t2 = ez->vec_and(a, b);
+			std::vector<int> t3 = ez->vec_and(c, t1);
+			ez->assume(ez->vec_eq(xx, ez->vec_or(t2, t3)));
+
+			if (model_undef)
+			{
+				std::vector<int> undef_a = importUndefSigSpec(cell->getPort("\\A"), timestep);
+				std::vector<int> undef_b = importUndefSigSpec(cell->getPort("\\B"), timestep);
+				std::vector<int> undef_c = importUndefSigSpec(cell->getPort("\\C"), timestep);
+
+				std::vector<int> undef_y = importUndefSigSpec(cell->getPort("\\Y"), timestep);
+				std::vector<int> undef_x = importUndefSigSpec(cell->getPort("\\X"), timestep);
+
+				ez->assume(ez->vec_eq(undef_y, ez->vec_or(ez->vec_or(undef_a, undef_b), undef_c)));
+
+				std::vector<int> undef_t1 = ez->vec_or(undef_a, undef_b);
+
+				std::vector<int> a0 = ez->vec_and(ez->vec_not(a), ez->vec_not(undef_a));
+				std::vector<int> b0 = ez->vec_and(ez->vec_not(b), ez->vec_not(undef_b));
+				std::vector<int> undef_t2 = ez->vec_and(ez->vec_or(undef_a, undef_b), ez->vec_not(ez->vec_or(a0, b0)));
+
+				std::vector<int> c0 = ez->vec_and(ez->vec_not(c), ez->vec_not(undef_c));
+				std::vector<int> t10 = ez->vec_and(ez->vec_not(t1), ez->vec_not(undef_t1));
+				std::vector<int> undef_t3 = ez->vec_and(ez->vec_or(undef_c, undef_t1), ez->vec_not(ez->vec_or(c0, t10)));
+
+				std::vector<int> t21 = ez->vec_and(t2, ez->vec_not(undef_t2));
+				std::vector<int> t31 = ez->vec_and(t3, ez->vec_not(undef_t3));
+				ez->assume(ez->vec_eq(undef_x, ez->vec_and(ez->vec_or(undef_t2, undef_t3), ez->vec_not(ez->vec_or(t21, t31)))));
+
+				undefGating(y, yy, undef_y);
+				undefGating(x, xx, undef_x);
+			}
+			return true;
+		}
+
 		if (cell->type == "$alu")
 		{
 			std::vector<int> a = importDefSigSpec(cell->getPort("\\A"), timestep);