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// ============================================================================
//        __
//   \\__/ o\    (C) 2006-2022  Robert Finch, Waterloo
//    \  __ /    All rights reserved.
//     \/_//     robfinch<remove>@finitron.ca
//       ||
//
//      dfdiv.v
//    Decimal Float divider primitive
//
// 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
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//
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//
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//                                                                          
// ============================================================================

module dfdiv(clk, ld, a, b, q, r, done, lzcnt);
parameter N=33;
localparam FPWID = N*4;
parameter RADIX = 10;
localparam FPWID1 = FPWID;//((FPWID+2)/3)*3;    // make FPWIDth a multiple of three
localparam DMSB = FPWID1-1;
input clk;
input ld;
input [FPWID-1:0] a;
input [FPWID-1:0] b;
output reg [FPWID*2-1:0] q;
output reg [FPWID-1:0] r;
output reg done;
output reg [7:0] lzcnt; // Leading zero digit count as a BCD number


reg [1:0] st;
parameter IDLE = 2'd0;
parameter SUBN = 2'd1;
parameter DONE = 2'd2;

reg [3:0] cnt;                          // iteration count
wire [3:0] cntm1 = cnt;//cnt==4'd0 ? 4'd9 : cnt-1'd1;
reg [7:0] dcnt;                         // digit count
reg [15:0] clkcnt;
reg [5:0] digcnt;
reg [FPWID*2-1:0] qi;
reg [FPWID+3:0] ri;
reg [FPWID-1:0] bi;
wire sgn;
wire [FPWID+3:0] dif; 
reg gotnz;                                      // got a non-zero digit

generate begin : gSub
BCDSubtract #(.N(N+1)) ubcds1
(
        .clk(clk),
        .a(ri),
        .b({4'b0,bi}),
        .o(dif),
        .sgn(sgn)
);
end
endgenerate

reg nz;
reg [N*2-1:0] zc;
genvar g;
generate begin : glzcnt
        for (g = N*2-1; g >= 0; g = g - 1)
        always_comb
                zc[g] = qi[g*4+3:g*4]==0;
end
endgenerate

integer n;
always_comb
begin
        nz = 1'b0;
        lzcnt = 'd0;
        for (n = N*2-1; n >= 0; n = n - 1)
        begin
                nz = nz | ~zc[n];
                if (!nz)
                        lzcnt = lzcnt + 1;
        end
end

always @(posedge clk)
begin
case(st)
IDLE:
        begin
                qi <= 'd0;
                ri <= 'd0;
        end
SUBN:
        begin
                digcnt <= digcnt - 1'd1;
                if (digcnt=='d0) begin
                        clkcnt <= clkcnt + 1'd1;
                        digcnt <= 6'd10;
                        if (bi > ri) begin
                                ri <= {ri,qi[FPWID*2-1:FPWID*2-4]};
                                qi <= {qi[FPWID*2-5:0],cnt};
                                cnt <= 4'd0;
                                dcnt <= dcnt - 1'd1;
                                if (dcnt=='d0)
                                        st <= DONE;
                        end
                        else begin
                                if (clkcnt > 600 && 0) begin
                                        ri <= {ri,qi[FPWID*2-1:FPWID*2-4]};
                                        qi <= {qi[FPWID*2-5:0],cntm1};
                                        cnt <= 4'd0;
                                        dcnt <= dcnt - 1'd1;
                                        if (dcnt==6'd0)
                                                st <= DONE;
                                end
                                else
                                begin
                                        ri <= dif;
                                        cnt <= cnt + 1'd1;
                                end
                        end
                end
        end
DONE:
        begin
                q <= qi;
                r <= ri;
                done <= 1'b1;
        end
default:
        st <= IDLE;
endcase
if (ld) begin
        clkcnt <= 10'd0;
        cnt <= 4'd0;
        digcnt <= 6'd10;
        dcnt <= $ceil(FPWID*2/4);
        qi <= {a,{FPWID{1'd0}}};
        ri <= {FPWID{1'd0}};
        bi <= b;
        st <= SUBN;
        done <= 1'b0;
end
end

endmodule

module dfdiv_tb();

reg clk;
reg ld;
reg [135:0] a, b;
wire [271:0] q;
wire [135:0] r;
wire [7:0] lzcnt;

initial begin
        clk = 1'b0;
        ld = 1'b0;
        a = 136'h50_00000000_00000000_00000000_00000000;
        b = 136'h50_00000000_00000000_00000000_00000000;
        #20 ld = 1'b1;
        #40 ld = 1'b0;
end

always #5 clk = ~clk;

dfdiv #(.N(34)) u1 (
        .clk(clk),
        .ld(ld), 
        .a(a),
        .b(b),
        .q(q),
        .r(r), 
        .done(done),
        .lzcnt(lzcnt)
);
endmodule