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////////////////////////////////////////////////////////////////////////////////
//
// Filename: 	bigsub.v
//
// Project:	OpenArty, an entirely open SoC based upon the Arty platform
//
// Purpose:	
//
// Creator:	Dan Gisselquist, Ph.D.
//		Gisselquist Technology, LLC
//
////////////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2016, Gisselquist Technology, LLC
//
// This program is free software (firmware): you can redistribute it and/or
// modify it under the terms of  the GNU General Public License as published
// by the Free Software Foundation, either version 3 of the License, or (at
// your option) any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
// for more details.
//
// You should have received a copy of the GNU General Public License along
// with this program.  (It's in the $(ROOT)/doc directory, run make with no
// target there if the PDF file isn't present.)  If not, see
// <http://www.gnu.org/licenses/> for a copy.
//
// License:	GPL, v3, as defined and found on www.gnu.org,
//		http://www.gnu.org/licenses/gpl.html
//
//
////////////////////////////////////////////////////////////////////////////////
//
//
module	bigsub(i_clk, i_sync, i_a, i_b, o_r, o_sync);
	input			i_clk, i_sync;
	input		[63:0]	i_a, i_b;
	output	reg	[63:0]	o_r;
	output	reg	o_sync;
 
	reg		r_sync, r_pps;
	reg	[31:0]	r_hi_a, r_hi_b, r_low;
 
	initial	r_sync = 1'b0;
	always @(posedge i_clk)
		r_sync <= i_sync;
 
	always @(posedge i_clk)
		{ r_pps, r_low } <= i_a[31:0] + ({1'b1,~i_b[31:0]}) + 1'b1;
	always @(posedge i_clk)
		r_hi_a <= i_a[63:32];
	always @(posedge i_clk)
		r_hi_b <= ~i_b[63:32];
 
	initial	o_sync = 1'b0;
	always @(posedge i_clk)
		o_sync <= r_sync;
	always @(posedge i_clk)
		o_r[31:0] <= r_low;
	always @(posedge i_clk)
		o_r[63:32] <= r_hi_a + r_hi_b + { 31'h00, r_pps };
 
endmodule