//======================================================================
//
// modexpa7_pe_sub.v
// -----------------------------------------------------------------------------
// Low-level processing element (subtractor).
//
// Authors: Pavel Shatov
//
// Copyright (c) 2017, NORDUnet A/S All rights reserved.
//
// 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
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//
// - 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
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// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//======================================================================

module modexpa7_pe_sub
	(
		input					clk,
		input					ce,
		input		[31: 0]	a,
		input		[31: 0]	b,
		input					b_in,
		output	[31: 0]	d,
		output				b_out
	);
	
	reg	[32: 0]	d_reg;
	
	assign d			= d_reg[31: 0];
	assign b_out	= d_reg[32];
	
	always @(posedge clk)
		//
		if (ce) d_reg <= {1'b0, a} - {1'b0, b} - {32'd0, b_in};

endmodule

//======================================================================
// End of file
//======================================================================