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// ============================================================================
//        __
//   \\__/ o\    (C) 2006-2020  Robert Finch, Waterloo
//    \  __ /    All rights reserved.
//     \/_//     robfinch<remove>@finitron.ca
//       ||
//
//      DFPRound128.sv
//    - decimal floating point rounding unit
//    - parameterized width
//
//
// 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:
//
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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