/*******************************************************************************
 * Module: masked_max_reg
 * Date:2015-01-09  
 * Author: Andrey Filippov     
 * Description: Finds maximal of two masked values, registers result
 *
 * Copyright (c) 2015 Elphel, Inc.
 * masked_max_reg.v is free software; 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.
 *
 *  masked_max_reg.v 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/> .
 *******************************************************************************/
`timescale 1ns/1ps

module  masked_max_reg#(
    parameter width=16
    )(
    input              clk,
    input  [width-1:0] a,
    input              mask_a,
    input  [width-1:0] b,
    input              mask_b,
    output [width-1:0] max,
    output             s,
    output             valid // at least one of the inputs was valid (matches outputs)
);
    reg    [width-1:0] max_r;
    reg                s_r;
    reg                valid_r;
    assign s=s_r;
    assign max=max_r;
    assign valid=valid_r;
//    wire s_w= mask_b && ((mask_a && (b>a)) || !mask_a);
    wire s_w= mask_b && (!mask_a || (b>a));
    always @ (posedge clk) begin
        s_r <= s_w;
        max_r <= (mask_a || mask_b)? (s_w?b:a): {width{1'b0}};
        valid_r <= mask_a || mask_b;
    end 
endmodule