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`timescale 1ns / 1ps
// ============================================================================
//        __
//   \\__/ o\    (C) 2022  Robert Finch, Waterloo
//    \  __ /    All rights reserved.
//     \/_//     robfinch<remove>@finitron.ca
//       ||
//
//      DDBCDToBin.sv
//  Uses the Dubble Dabble algorithm
//
// BSD 3-Clause License
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this
//    list of conditions and the following disclaimer.
//
// 2. 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.
//
// 3. Neither the name of the copyright holder 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
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// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//                                                                          
// ============================================================================
//
module DDBCDToBin(rst, clk, ld, bcd, bin, done);
parameter WID = 128;
parameter DEP = 2;              // cascade depth
localparam BCDWID = ((WID+(WID-4)/3)+3) & -4;
input rst;
input clk;
input ld;
input [BCDWID-1:0] bcd;
output reg [WID-1:0] bin;
output reg done;

integer k;
genvar n,g;
reg [WID-1:0] binw, binwt;                      // working binary value
reg [BCDWID-1:0] bcdwt;
reg [BCDWID-1:0] bcdw [0:DEP];  // working bcd value
reg [7:0] bitcnt;
reg [2:0] state;
parameter IDLE = 3'd0;
parameter CHK5 = 3'd1;
parameter SHFT = 3'd2;
parameter DONE = 3'd3;

function [BCDWID-1:0] fnRow;
input [BCDWID-1:0] i;
begin
        fnRow = 'd0;
        for (k = 0; k < BCDWID; k = k + 4)
                if (((i >> k) & 4'hF) >= 4'd8)
                        fnRow = fnRow | (((i >> k) & 4'hF) - 4'd3) << k;
                else
                        fnRow = fnRow | ((i >> k) & 4'hf) << k;
end
endfunction

always_comb
        bcdw[0] = bcdwt;
generate begin : gRows
        for (n = 0; n < DEP; n = n + 1)
                always_comb
                begin
                        binwt[WID-DEP+n] = bcdw[n][0];
                        bcdw[n+1] = fnRow({1'b0,bcdw[n][BCDWID-1:1]});
                end
end
endgenerate

always_ff @(posedge clk)
if (rst) begin
        state <= IDLE;
        done <= 1'b1;
        bcdwt <= 'd0;
        binw <= 'd0;
        bitcnt <= 'd0;
        bin <= 'd0;
end
else begin
        if (ld) begin
                done <= 1'b0;
                bitcnt <= (WID+DEP-1)/DEP-1;
                binw <= 'd0;
                bcdwt <= bcd;
                state <= SHFT;
        end
        else
        case(state)
        IDLE:   ;
        SHFT:
                begin
                        bitcnt <= bitcnt - 2'd1;
                        if (bitcnt==8'd0) begin
                                state <= DONE;
                        end
                        bcdwt <= bcdw[DEP];
                        binw <= {binwt[WID-1:WID-DEP],binw[WID-1:DEP]};
                end
        DONE:
                begin
                        bin <= binw;
                        done <= 1'b1;
                        state <= IDLE;
                end
        default:
                state <= IDLE;
        endcase
end


endmodule