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// ============================================================================

//        __

//   \\__/ o\    (C) 2022  Robert Finch, Waterloo

//    \  __ /    All rights reserved.

//     \/_//     robfinch@finitron.ca

//       ||

//

//      i2df128.sv

//  - convert integer to decimal floating point

//

// 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

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//    this software without specific prior written permission.

//

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

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//

// ============================================================================

import DFPPkg::*;

module i2df128 (rst, clk, ce, ld, op, rm, i, o, done);

parameter FPWID=128;

input rst;

input clk;

input ce;

input ld;

input op;                                               // 1 = signed, 0 = unsigned

input [2:0] rm;                 // rounding mode

input [127:0] i;                // integer input

output [127:0] o;               // float output

output done;

wire [127:0] i1 = (op & i[127]) ? -i : i;

wire [171:0] bcd;

wire done1, done2;

assign done = done1 & done2;

DDBinToBCD ub2b1

(

        .rst(rst),

        .clk(clk),

        .ld(ld),

        .bin(i1),

        .bcd(bcd),

        .done(done1)

);

DFP128U ui;

wire [13:0] zeroXp = {13{1'b1}};

reg iz;                 // zero input ?

wire [7:0] lz;          // count the leading zeros in the number

reg [7:0] lz4;          // leading zero rounded to multiple of four

wire [13:0] wd; // compute number of whole digits

reg so;                 // copy the sign of the input (easy)

reg [2:0] rmd;

wire [171:0] bcd1;

reg [135:0] simag;

always_ff @(posedge clk)

        rmd <= rm;

always_ff @(posedge clk)

        iz <= i==0;

always_ff @(posedge clk)

        so <= i[127];

delay1 #(172) u2 (.clk(clk), .ce(ce), .i(bcd),  .o(bcd1) );

cntlz192Reg   u4 (.clk(clk), .ce(ce), .i({bcd,20'd0}), .o(lz) );

always_comb

        lz4 = lz >> 2'd2;

assign wd = zeroXp - 8'd1 + 8'd34 - lz4 + 8'd9; // constant except for lz

reg [13:0] xo;

always_ff @(posedge clk)

        xo <= iz ? 'd0 : wd;

// left align number

// The number may to too large to represent entirely precisely in which case a

// right shift is required. There are only about 114 bits of precision, but the

// incoming number is allowed to be 128-bit.

// Rounding is required only when the number needs to be right-shifted.

always_ff @(posedge clk)

        if (lz4 < 8'd9)

                simag = bcd1 >> {8'd9 - lz4,2'd0};

        else

                simag = bcd1 << {lz4 - 8'd9,2'd0};

wire g =  bcd1[{8'd9 - lz4,2'd0}];      // guard bit (lsb)

wire r =        bcd1[{8'd9 - lz4,2'd0}-1];      // rounding bit

wire s = |(bcd1 & (172'd1 << {8'd9 - lz4,2'd0}-2) - 2'd1);       // "sticky" bit

reg rnd;

// Compute the round bit

always_ff @(posedge clk)

if (lz4 < 8'd9)

        case (rmd)

        3'd0:   rnd = (g & r) | (r & s);      // round to nearest even

        3'd1:   rnd = 0;                                        // round to zero (truncate)

        3'd2:   rnd = (r | s) & !so;         // round towards +infinity

        3'd3:   rnd = (r | s) & so;                 // round towards -infinity

        3'd4:   rnd = (r | s);

        default:        rnd = (g & r) | (r & s);      // round to nearest even

        endcase

else

        rnd = 1'b0;

// round the result

assign ui.sig = simag[135:0] + rnd;

assign ui.exp = xo[13:0];

assign ui.sign = op & so;

assign ui.nan = 1'b0;

assign ui.qnan = 1'b0;

assign ui.snan = 1'b0;

assign ui.infinity = 1'b0;

DFPPack128 upk1 (ui, o);

ft_delay #(.WID(1), .DEP(4)) udly1 (.clk(clk), .ce(1'b1), .i(done1), .o(done2));

endmodule