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/*

    Copyright 2011, City University of Hong Kong

    Author is Homer (Dongsheng) Xing.

    This file is part of Elliptic Curve Group Core.

    Elliptic Curve Group Core is free software: you can redistribute it and/or modify

    it under the terms of the GNU Lesser General Public License as published by

    the Free Software Foundation, either version 3 of the License, or

    (at your option) any later version.

    Elliptic Curve Group Core is distributed in the hope that it will be useful,

    but WITHOUT ANY WARRANTY; without even the implied warranty of

    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU General Public License

    along with Elliptic Curve Group Core.  If not, see http://www.gnu.org/licenses/lgpl.txt

*/

`define SCALAR_WIDTH (151-1) // the width for the scalar value

/* $P3(x3,y3) == c \cdot P1(x1,y1)$ */

module point_scalar_mult(clk, reset, x1, y1, zero1, c, done, x3, y3, zero3);

    input clk, reset;

    input [`WIDTH:0] x1, y1;

    input zero1;

    input [`SCALAR_WIDTH:0] c;

    output reg done;

    output reg [`WIDTH:0] x3, y3;

    output reg zero3;

    reg [`WIDTH:0] x2, y2; reg zero2; // the result

    wire [`WIDTH:0] x4, y4; wire zero4;

    wire [`WIDTH:0] x5, y5; wire zero5;

    reg [`SCALAR_WIDTH   : 0] k; // the scalar value

    reg [`SCALAR_WIDTH+1 : 0] i; // the counter

    reg op;

    wire p, p2, rst, done1;

    assign x4    = (~op) ? x2    : (k[`SCALAR_WIDTH]?x1:0);

    assign y4    = (~op) ? y2    : (k[`SCALAR_WIDTH]?y1:0);

    assign zero4 = (~op) ? zero2 : (k[`SCALAR_WIDTH]?zero1:1);

    assign rst   = reset | p2 ;

    point_add

        ins1 (clk, rst, x2, y2, zero2, x4, y4, zero4, done1, x5, y5, zero5);

    func6

        ins2 (clk, reset, done1, p),

        ins3 (clk, reset, p, p2);

    always @ (posedge clk)

        if (reset) i <= 1;

        else if ((op & p) | i[`SCALAR_WIDTH+1]) i <= i << 1;

    always @ (posedge clk)

        if (reset) k <= c;

        else if (op & p) k <= k << 1;

    always @ (posedge clk)

        if (reset) op <= 0;

        else if (p) op <= ~op;

    always @ (posedge clk)

        if (reset)  begin x2 <= 0; y2 <= 0; zero2 <= 1; end

        else if (p) begin x2 <= x5; y2 <= y5; zero2 <= zero5; end

    always @ (posedge clk)

        if (reset)  begin x3 <= 0; y3 <= 0; zero3 <= 1; done <= 0; end

        else if (i[`SCALAR_WIDTH+1])

          begin x3 <= x2; y3 <= y2; zero3 <= zero2; done <= 1; end

endmodule

/* add two points on the elliptic curve $y^2=x^3-x+1$ over a Galois field GF(3^M)

 * whose irreducible polynomial is $x^97 + x^12 + 2$. */