Added primitives with clock enable ports.

Added primitives from ModExp.

8 files changed, 532 insertions, 16 deletions

diff --git a/lowlevel/artix7/adder32_ce_artix7.v b/lowlevel/artix7/adder32_ce_artix7.v
new file mode 100644
index 0000000..0f6d44d
--- /dev/null
+++ b/lowlevel/artix7/adder32_ce_artix7.v
@@ -0,0 +1,97 @@
+//------------------------------------------------------------------------------
+//
+// adder32_ce_artix7.v
+// -----------------------------------------------------------------------------
+// Hardware (Artix-7 DSP48E1) 32-bit adder w/ clock enable.
+//
+// Authors: Pavel Shatov
+//
+// Copyright (c) 2016, 2018 NORDUnet A/S
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// - Neither the name of the NORDUnet nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+//------------------------------------------------------------------------------
+
+module adder32_ce_artix7
+  (
+   input 	  clk, // clock
+   input      ce, // clock enable
+   input [31: 0]  a, // operand input
+   input [31: 0]  b, // operand input
+   output [31: 0] s, // sum output
+   input 	  c_in, // carry input
+   output 	  c_out		// carry output
+   );
+
+   //
+   // Lower and higher parts of operand
+   //
+   wire [17: 0]   bl = b[17: 0];
+   wire [13: 0]   bh = b[31:18];
+
+
+   //
+   // DSP48E1 Slice
+   //
+
+   /* Operation Mode */
+   wire [ 3: 0]   dsp48e1_alumode	= 4'b0000;
+   wire [ 6: 0]   dsp48e1_opmode		= 7'b0110011;
+
+   /* Internal Product */
+   wire [47: 0]   p_int;
+
+   dsp48e1_wrapper dsp_adder
+     (
+      .clk			(clk),
+
+      .ce			(ce),
+
+      .carry		(c_in),
+
+      .alumode		(dsp48e1_alumode),
+      .opmode		(dsp48e1_opmode),
+
+      .a				({{16{1'b0}}, bh}),
+      .b				(bl),
+      .c				({{16{1'b0}}, a}),
+
+      .p				(p_int)
+      );
+
+   //
+   // Output Mapping
+   //
+   assign s 		= p_int[31: 0];
+   assign c_out	= p_int[32];
+
+
+endmodule
+
+//------------------------------------------------------------------------------
+// End-of-File
+//------------------------------------------------------------------------------
diff --git a/lowlevel/artix7/dsp48e1_wrapper_modexp.v b/lowlevel/artix7/dsp48e1_wrapper_modexp.v
index 17d8efe..27c8bf8 100644
--- a/lowlevel/artix7/dsp48e1_wrapper_modexp.v
+++ b/lowlevel/artix7/dsp48e1_wrapper_modexp.v
@@ -36,7 +36,7 @@
 //
 //------------------------------------------------------------------------------
 
-module modexpa7_dsp48e1_wrapper_modexp #
+module dsp48e1_wrapper_modexp #
 	(
 		parameter	AREG		= 1'b0,
 		parameter	PREG		= 1'b0,
diff --git a/lowlevel/artix7/modexp_multiplier32_artix7.v b/lowlevel/artix7/modexp_multiplier32_artix7.v
new file mode 100644
index 0000000..d4bd3f4
--- /dev/null
+++ b/lowlevel/artix7/modexp_multiplier32_artix7.v
@@ -0,0 +1,171 @@
+//------------------------------------------------------------------------------
+//
+// modexp_multiplier32_artix7.v
+// -----------------------------------------------------------------------------
+// Hardware (Artix-7 DSP48E1) 32-bit multiplier.
+//
+// Authors: Pavel Shatov
+//
+// Copyright (c) 2016-2017, NORDUnet A/S
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// - Neither the name of the NORDUnet nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+//------------------------------------------------------------------------------
+
+module modexp_multiplier32_artix7
+	(
+		input					clk,
+		input		[31: 0]	a,
+		input		[31: 0]	b,
+		output	[63: 0]	p
+	);
+
+		/* split a, b into smaller words */
+	wire	[16: 0]	a_lo = a[16: 0];
+	wire	[16: 0]	b_lo = b[16: 0];
+	wire	[14: 0]	a_hi = a[31:17];
+	wire	[14: 0]	b_hi = b[31:17];
+
+		/* smaller sub-products */
+	wire	[47: 0]	dsp1_p;
+	wire	[47: 0]	dsp2_p;
+	wire	[47: 0]	dsp4_p;
+
+		/* direct output mapping */
+	assign p[63:34] = dsp4_p[29: 0];
+	
+		/* delayed output mapping */
+	genvar fd;
+	generate for (fd=0; fd<17; fd=fd+1)
+		begin : gen_FD
+			FD # (.INIT( 1'b0)) FD_inst1 (.C(clk), .D(dsp1_p[fd]), .Q(p[fd +  0]));
+			FD # (.INIT( 1'b0)) FD_inst3 (.C(clk), .D(dsp2_p[fd]), .Q(p[fd + 17]));
+		end
+	endgenerate
+
+		/* product chains */
+	wire	[47: 0]	dsp1_p_chain;
+	wire	[47: 0]	dsp3_p_chain;
+	wire	[47: 0]	dsp2_p_chain;
+	
+		/* operand chains */
+	wire	[29: 0]	a_lo_chain;
+	wire	[29: 0]	a_hi_chain;  
+  
+		//
+		// a_lo * b_lo
+		//
+	dsp48e1_wrapper_modexp #
+	(
+		.AREG			(1'b1),
+		.PREG			(1'b0),
+		.A_INPUT		("DIRECT")
+	)
+	dsp1
+	(
+		.clk		(clk),
+		.opmode	(7'b0110101),
+		.a			({13'd0, a_lo}),
+		.b			({1'b0, b_lo}),
+		.p			(dsp1_p),
+		.acin		(30'd0),
+		.pcin		(48'd0),
+		.acout	(a_lo_chain),
+		.pcout	(dsp1_p_chain)
+	);
+	
+		//
+		// a_hi * b_lo
+		//
+	dsp48e1_wrapper_modexp #
+	(
+		.AREG			(1'b1),
+		.PREG			(1'b0),
+		.A_INPUT		("DIRECT")
+	)
+	dsp2
+	(
+		.clk		(clk),
+		.opmode	(7'b0010101),
+		.a			({15'd0, a_hi}),
+		.b			({1'd0, b_lo}),
+		.p			(dsp2_p),
+		.acin		(30'd0),
+		.pcin		(dsp3_p_chain),
+		.acout	(a_hi_chain),
+		.pcout	(dsp2_p_chain)
+	);
+	
+		//
+		// a_lo * b_hi
+		//
+	dsp48e1_wrapper_modexp #
+	(
+		.AREG			(1'b0),
+		.PREG			(1'b0),
+		.A_INPUT		("CASCADE")
+	)
+	dsp3
+	(
+		.clk		(clk),
+		.opmode	(7'b1010101),
+		.a			(30'd0),
+		.b			({3'd0, b_hi}),
+		.p			(),
+		.acin		(a_lo_chain),
+		.pcin		(dsp1_p_chain),
+		.acout	(),
+		.pcout	(dsp3_p_chain)
+	);	
+	
+		//
+		// a_hi * b_hi
+		//
+	dsp48e1_wrapper_modexp #
+	(
+		.AREG			(1'b0),
+		.PREG			(1'b1),
+		.A_INPUT		("CASCADE")
+	)
+	dsp4
+	(
+		.clk		(clk),
+		.opmode	(7'b1010101),
+		.a			(30'd0),
+		.b			({3'd0, b_hi}),
+		.p			(dsp4_p),
+		.acin		(a_hi_chain),
+		.pcin		(dsp2_p_chain),
+		.acout	(),
+		.pcout	()
+	);
+
+endmodule
+
+//------------------------------------------------------------------------------
+// End-of-File
+//------------------------------------------------------------------------------
diff --git a/lowlevel/artix7/modexp_systolic_pe_artix7.v b/lowlevel/artix7/modexp_systolic_pe_artix7.v
index 08391f5..9cf01f2 100644
--- a/lowlevel/artix7/modexp_systolic_pe_artix7.v
+++ b/lowlevel/artix7/modexp_systolic_pe_artix7.v
@@ -60,10 +60,9 @@ module modexp_systolic_pe_artix7
 	
 	always @(posedge clk) t_c_in_c_out_dly <= t_c_in_c_out;
 	
-	modexpa7_adder32_artix7 add_t_c_in
+	adder32_artix7 add_t_c_in
 	(
 		.clk		(clk),
-		.ce		(1'b1),
 		.a			(t_dly),
 		.b			(c_in_dly),
 		.c_in		(1'b0),
@@ -80,7 +79,7 @@ module modexp_systolic_pe_artix7
 	
 	always @(posedge clk) a_b_msb_dly <= a_b_msb;
 	
-	modexpa7_multiplier32_artix7 mul_a_b
+	modexp_multiplier32_artix7 mul_a_b
 	(
 		.clk	(clk),
 		.a		(a),
@@ -97,10 +96,9 @@ module modexp_systolic_pe_artix7
 	
 	assign p = add_p_s_dly;
 	
-	modexpa7_adder32_artix7 add_p
+	adder32_artix7 add_p
 	(
 		.clk		(clk),
-		.ce		(1'b1),
 		.a			(a_b_lsb),
 		.b			(t_c_in_s),
 		.c_in		(1'b0),
@@ -108,10 +106,9 @@ module modexp_systolic_pe_artix7
 		.c_out	(add_p_c_out)
 	);
 
-	modexpa7_adder32_artix7 add_c_out
+	adder32_artix7 add_c_out
 	(
 		.clk		(clk),
-		.ce		(1'b1),
 		.a			(a_b_msb_dly),
 		.b			({{31{1'b0}}, t_c_in_c_out_dly}),
 		.c_in		(add_p_c_out),
diff --git a/lowlevel/artix7/subtractor32_ce_artix7.v b/lowlevel/artix7/subtractor32_ce_artix7.v
new file mode 100644
index 0000000..c0238ea
--- /dev/null
+++ b/lowlevel/artix7/subtractor32_ce_artix7.v
@@ -0,0 +1,95 @@
+//------------------------------------------------------------------------------
+//
+// subtractor32_ce_artix7.v
+// -----------------------------------------------------------------------------
+// Hardware (Artix-7 DSP48E1) 32-bit subtractor w/ clock enable.
+//
+// Authors: Pavel Shatov
+//
+// Copyright (c) 2016, NORDUnet A/S
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// - Neither the name of the NORDUnet nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+//------------------------------------------------------------------------------
+
+module subtractor32_ce_artix7
+  (
+   input 	  clk,
+   input      ce,
+   input [31: 0]  a,
+   input [31: 0]  b,
+   output [31: 0] d,
+   input 	  b_in,
+   output 	  b_out
+   );
+
+   //
+   // Lower and higher parts of operand
+   //
+   wire [17: 0]   bl = b[17: 0];
+   wire [13: 0]   bh = b[31:18];
+
+   //
+   // DSP48E1 Slice
+   //
+
+   /* Operation Mode */
+   wire [ 3: 0]   dsp48e1_alumode	= 4'b0011;
+   wire [ 6: 0]   dsp48e1_opmode		= 7'b0110011;
+
+   /* Internal Product */
+   wire [47: 0]   p_int;
+
+   dsp48e1_wrapper dsp_subtractor
+     (
+      .clk			(clk),
+
+      .ce			(ce),
+
+      .carry		(b_in),
+
+      .alumode		(dsp48e1_alumode),
+      .opmode		(dsp48e1_opmode),
+
+      .a				({{16{1'b0}}, bh}),
+      .b				(bl),
+      .c				({{16{1'b0}}, a}),
+
+      .p				(p_int)
+      );
+
+   //
+   // Output Mapping
+   //
+   assign d 		= p_int[31: 0];
+   assign b_out	= p_int[32];
+
+endmodule
+
+//------------------------------------------------------------------------------
+// End-of-File
+//------------------------------------------------------------------------------
diff --git a/lowlevel/cryptech_primitive_switch.vh b/lowlevel/cryptech_primitive_switch.vh
index a4aad45..44b0852 100644
--- a/lowlevel/cryptech_primitive_switch.vh
+++ b/lowlevel/cryptech_primitive_switch.vh
@@ -49,19 +49,29 @@
     //
     // Generic Math Primitives
     //
-`define CRYPTECH_PRIMITIVE_MAC16_GENERIC    mac16_generic
-`define CRYPTECH_PRIMITIVE_ADD32_GENERIC    adder32_generic
-`define CRYPTECH_PRIMITIVE_ADD47_GENERIC    adder47_generic
-`define CRYPTECH_PRIMITIVE_SUB32_GENERIC    subtractor32_generic
+`define CRYPTECH_PRIMITIVE_MAC16_GENERIC mac16_generic
+`define CRYPTECH_PRIMITIVE_ADD32_GENERIC adder32_generic
+`define CRYPTECH_PRIMITIVE_ADD47_GENERIC adder47_generic
+`define CRYPTECH_PRIMITIVE_SUB32_GENERIC subtractor32_generic
+
+`define CRYPTECH_PRIMITIVE_ADD32_CE_GENERIC adder32_ce_generic
+`define CRYPTECH_PRIMITIVE_SUB32_CE_GENERIC subtractor32_ce_generic
+
+`define CRYPTECH_PRIMITIVE_MODEXP_SYSTOLIC_PE_GENERIC modexp_systolic_pe_generic
     
 
     //
     // Xilinx Math Primitives for Artix-7 Family
     //
-`define CRYPTECH_PRIMITIVE_MAC16_VENDOR     mac16_artix7
-`define CRYPTECH_PRIMITIVE_ADD32_VENDOR     adder32_artix7
-`define CRYPTECH_PRIMITIVE_ADD47_VENDOR     adder47_artix7
-`define CRYPTECH_PRIMITIVE_SUB32_VENDOR     subtractor32_artix7
+`define CRYPTECH_PRIMITIVE_MAC16_VENDOR  mac16_artix7
+`define CRYPTECH_PRIMITIVE_ADD32_VENDOR  adder32_artix7
+`define CRYPTECH_PRIMITIVE_ADD47_VENDOR  adder47_artix7
+`define CRYPTECH_PRIMITIVE_SUB32_VENDOR  subtractor32_artix7
+
+`define CRYPTECH_PRIMITIVE_ADD32_CE_VENDOR adder32_ce_artix7
+`define CRYPTECH_PRIMITIVE_SUB32_CE_VENDOR subtractor32_ce_artix7
+
+`define CRYPTECH_PRIMITIVE_MODEXP_SYSTOLIC_PE_VENDOR modexp_systolic_pe_artix7
 
 
 
@@ -78,6 +88,11 @@
 `define CRYPTECH_PRIMITIVE_ADD47 `CRYPTECH_PRIMITIVE_ADD47_GENERIC
 `define CRYPTECH_PRIMITIVE_SUB32 `CRYPTECH_PRIMITIVE_SUB32_GENERIC
 
+`define CRYPTECH_PRIMITIVE_ADD32_CE `CRYPTECH_PRIMITIVE_ADD32_CE_GENERIC
+`define CRYPTECH_PRIMITIVE_SUB32_CE `CRYPTECH_PRIMITIVE_SUB32_CE_GENERIC
+
+`define CRYPTECH_PRIMITIVE_MODEXP_SYSTOLIC_PE `CRYPTECH_PRIMITIVE_MODEXP_SYSTOLIC_PE_GENERIC
+
 `else
 
     // vendor-specific primitives
@@ -86,6 +101,11 @@
 `define CRYPTECH_PRIMITIVE_ADD32 `CRYPTECH_PRIMITIVE_ADD32_VENDOR
 `define CRYPTECH_PRIMITIVE_SUB32 `CRYPTECH_PRIMITIVE_SUB32_VENDOR
 
+`define CRYPTECH_PRIMITIVE_ADD32_CE `CRYPTECH_PRIMITIVE_ADD32_CE_VENDOR
+`define CRYPTECH_PRIMITIVE_SUB32_CE `CRYPTECH_PRIMITIVE_SUB32_CE_VENDOR
+
+`define CRYPTECH_PRIMITIVE_MODEXP_SYSTOLIC_PE `CRYPTECH_PRIMITIVE_MODEXP_SYSTOLIC_PE_VENDOR
+
 `endif
 
 
diff --git a/lowlevel/generic/adder32_ce_generic.v b/lowlevel/generic/adder32_ce_generic.v
new file mode 100644
index 0000000..329bcbf
--- /dev/null
+++ b/lowlevel/generic/adder32_ce_generic.v
@@ -0,0 +1,68 @@
+//------------------------------------------------------------------------------
+//
+// adder32_ce_generic.v
+// -----------------------------------------------------------------------------
+// Generic 32-bit adder w/ clock enable.
+//
+// Authors: Pavel Shatov
+//
+// Copyright (c) 2016, 2018 NORDUnet A/S
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// - Neither the name of the NORDUnet nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+//------------------------------------------------------------------------------
+
+module adder32_ce_generic
+  (
+   input 	  clk, // clock
+   input      ce, // clock enable
+   input [31: 0]  a, // operand input
+   input [31: 0]  b, // operand input
+   output [31: 0] s, // sum output
+   input 	  c_in, // carry input
+   output 	  c_out		// carry output
+   );
+
+   //
+   // Sum
+   //
+   reg [32: 0] 	  s_int;
+
+   always @(posedge clk)
+     if (ce) s_int <= {1'b0, a} + {1'b0, b} + {{32{1'b0}}, c_in};
+
+   //
+   // Output
+   //
+   assign s = s_int[31:0];
+   assign c_out = s_int[32];
+
+endmodule
+
+//------------------------------------------------------------------------------
+// End-of-File
+//------------------------------------------------------------------------------
diff --git a/lowlevel/generic/subtractor32_ce_generic.v b/lowlevel/generic/subtractor32_ce_generic.v
new file mode 100644
index 0000000..da97e76
--- /dev/null
+++ b/lowlevel/generic/subtractor32_ce_generic.v
@@ -0,0 +1,68 @@
+//------------------------------------------------------------------------------
+//
+// subtractor32_ce_generic.v
+// -----------------------------------------------------------------------------
+// Generic 32-bit subtractor w/ clock enable.
+//
+// Authors: Pavel Shatov
+//
+// Copyright (c) 2016, NORDUnet A/S
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// - Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+//
+// - Neither the name of the NORDUnet nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+//------------------------------------------------------------------------------
+
+module subtractor32_ce_generic
+  (
+   input 	  clk,
+   input      ce,
+   input [31: 0]  a,
+   input [31: 0]  b,
+   output [31: 0] d,
+   input 	  b_in,
+   output 	  b_out
+   );
+
+   //
+   // Difference
+   //
+   reg [32: 0] 	  d_int;
+
+   always @(posedge clk)
+     if (ce) d_int <= {1'b0, a} - {1'b0, b} - {{32{1'b0}}, b_in};
+
+   //
+   // Output
+   //
+   assign d = d_int[31:0];
+   assign b_out = d_int[32];
+
+endmodule
+
+//------------------------------------------------------------------------------
+// End-of-File
+//------------------------------------------------------------------------------