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

//        __

//   \\__/ o\    (C) 2006-2020  Robert Finch, Waterloo

//    \  __ /    All rights reserved.

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

//       ||

//

//      DFPRound128.sv

//    - decimal floating point rounding unit

//    - parameterized width

//

//

// BSD 3-Clause License

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// modification, are permitted provided that the following conditions are met:

//

// 1. Redistributions of source code must retain the above copyright notice, this

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

import DFPPkg::*;

`ifdef MIN_LATENCY

`define PIPE_ADV  *

`else

`define PIPE_ADV  (posedge clk)

`endif

module DFPRound128(clk, ce, rm, i, o);

parameter N=34;

input clk;

input ce;

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

input DFP128UN i;               // intermediate format input

output DFP128U o;               // rounded output

parameter ROUND_CEILING = 3'd0;

parameter ROUND_FLOOR = 3'd1;

parameter ROUND_HALF_UP = 3'd2;

parameter ROUND_HALF_EVEN = 3'd3;

parameter ROUND_DOWN = 3'd4;

//------------------------------------------------------------

// variables

wire nano, qnano, snano;

wire infinity;

wire so;

wire [13:0] xo;

reg  [N*4-1:0] mo;

reg [13:0] xo1;

reg [N*4-1:0] mo1;

wire xInf = i.exp==14'h3FFF;

wire so0 = i.sign;

assign o = {so,xo,mo};

assign o.nan = nano;

assign o.qnan = qnano;

assign o.snan = snano;

assign o.infinity = infinity;

assign o.sign = so;

assign o.exp = xo;

assign o.sig = mo;

wire [3:0] l = i.sig[7:4];

wire [3:0] r = i.sig[3:0];

reg rnd;

//------------------------------------------------------------

// Clock #1

// - determine round amount (add 1 or 0)

//------------------------------------------------------------

always @`PIPE_ADV

if (ce) xo1 <= i.exp;

always @`PIPE_ADV

if (ce) mo1 <= i.sig[(N+1)*4-1:4];

// Compute the round bit

// Infinities and NaNs are not rounded!

always @`PIPE_ADV

if (ce)

        if (i.nan | i.infinity)

                rnd = 1'b0;

        else

                case (rm)

                ROUND_CEILING:  rnd <= (r == 4'd0 || i.sign==1'b1) ? 1'b0 : 1'b1;

                ROUND_FLOOR:            rnd <= (r == 4'd0 || i.sign==1'b0) ? 1'b0 : 1'b1;

                ROUND_HALF_UP:  rnd <= r >= 4'h5;

                ROUND_HALF_EVEN:        rnd <= r==4'h5 ? l[0] : r > 4'h5 ? 1'b1 : 1'b0;

                ROUND_DOWN:                     rnd <= 1'b0;

                default:                                rnd <= 1'b0;

                endcase

//------------------------------------------------------------

// Clock #2

// round the number, check for carry

// note: inf. exponent checked above (if the exponent was infinite already, then no rounding occurs as rnd = 0)

// note: exponent increments if there is a carry (can only increment to infinity)

//------------------------------------------------------------

wire [N*4-1:0] rounded1;

wire cobcd;

BCDAddN #(.N(N)) ubcdan1

(

        .ci(1'b0),

        .a(mo1),

        .b({{N*4-1{1'd0}},rnd}),

        .o(rounded1),

        .co(cobcd)

);

reg [N*4-1:0] rounded2;

reg rnd2;

reg dn2;

reg [14:0] xo2;

always @`PIPE_ADV

        if (ce) rounded2 <= rounded1;

always @`PIPE_ADV

        if (ce) rnd2 <= rnd;

always @`PIPE_ADV

        if (ce) dn2 <= !(|xo1);

always @`PIPE_ADV

        if (ce) xo2 <= xo1 + cobcd;

//------------------------------------------------------------

// Clock #3

// - shift mantissa if required.

//------------------------------------------------------------

wire infinity2;

`ifdef MIN_LATENCY

assign nano = i.nan;

assign qnano = i.qnan;

assign snano = i.snan;

assign infinity = i.infinity | (rnd2 && xo2[13:0]==14'h3FFF);

assign so = i.sign;

assign xo = xo2[13:0];

`else

delay3 #(1) u21 (.clk(clk), .ce(ce), .i(i.nan), .o(nano));

delay3 #(1) u22 (.clk(clk), .ce(ce), .i(i.qnan), .o(qnano));

delay3 #(1) u23 (.clk(clk), .ce(ce), .i(i.snan), .o(snano));

delay2 #(1) u24 (.clk(clk), .ce(ce), .i(i.infinity), .o(infinity2));

delay3 #(1) u25 (.clk(clk), .ce(ce), .i(i.sign), .o(so));

delay1 #(14) u26 (.clk(clk), .ce(ce), .i(xo2[13:0]), .o(xo));

delay1 #(1) u27 (.clk(clk), .ce(ce), .i(infinity2 | (rnd2 && xo2[13:0]==14'h3FFF)), .o(infinity));

`endif

wire carry2 = xo2[14];

always @`PIPE_ADV

if (ce)

        casez({rnd2,xo2[13:0]==14'h3FFF,carry2,dn2})

        4'b0??0:        mo <= mo1[N*4-1:0];                                                     // not rounding, not denormalized

        4'b0??1:        mo <= mo1[N*4-1:0];                                                     // not rounding, denormalized

        4'b1000:        mo <= rounded2[N*4-1: 0];                               // exponent didn't change, number was normalized

        4'b1001:        mo <= rounded2[N*4-1: 0];                               // exponent didn't change, but number was denormalized

        4'b1010:        mo <= {4'h1,rounded2[N*4-1: 4]};        // exponent incremented (new MSD generated), number was normalized

        4'b1011:        mo <= rounded2[N*4-1:0];                                        // exponent incremented (new MSB generated), number was denormalized, number became normalized

        4'b11??:        mo <= {N*4{1'd0}};                                                                      // number became infinite, no need to check carry etc., rnd would be zero if input was NaN or infinite

        endcase

endmodule