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

//        __

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

//    \  __ /    All rights reserved.

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

//       ||

//

//      DFPNormalize.sv

//    - decimal floating point normalization unit

//    - eight cycle latency

//    - parameterized width

//

//

// This source file is free software: you can redistribute it and/or modify

// it under the terms of the GNU Lesser General Public License as published

// by the Free Software Foundation, either version 3 of the License, or

// (at your option) any later version.

//

// This source file is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

//

// You should have received a copy of the GNU General Public License

// along with this program.  If not, see .

//

//      This unit takes a floating point number in an intermediate

// format and normalizes it. No normalization occurs

// for NaN's or infinities. The unit has a two cycle latency.

//

// The mantissa is assumed to start with two whole bits on

// the left. The remaining bits are fractional.

//

// The width of the incoming format is reduced via a generation

// of sticky bit in place of the low order fractional bits.

//

// On an underflowed input, the incoming exponent is assumed

// to be negative. A right shift is needed.

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

import fp::*;

module DFPNormalize(clk, ce, i, o, under_i, under_o, inexact_o);

input clk;

input ce;

input [243:0] i;                // expanded format input

output [131:0] o;               // normalized output + guard, sticky and round bits, + 1 whole digit

input under_i;

output under_o;

output inexact_o;

integer n;

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

// No Clock required

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

reg [15:0] xo0;

reg so0;

reg sx0;

reg nan0;

reg inf0;

always @*

        xo0 <= i[239:224];

always @*

        so0 <= i[242];          // sign doesn't change

always @*

        sx0 <= i[240];

always @*

        nan0 <= i[243];

always @*

        inf0 <= i[241] || xo0==16'h9999 && i[220];

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

// Clock #1

// - Capture exponent information

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

reg xInf1a, xInf1b, xInf1c;

wire [243:0] i1;

delay #(.WID(244),.DEP(1)) u11 (.clk(clk), .ce(ce), .i(i), .o(i1));

always @(posedge clk)

        if (ce) xInf1a <= xo0==16'h9999 & !under_i;

always @(posedge clk)

        if (ce) xInf1b <= xo0==16'h9998 & !under_i;

always @(posedge clk)

        if (ce) xInf1c <= xo0==16'h9999;

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

// Clock #2

// - determine exponent increment

// Since the there are *three* whole digits in the incoming format

// the number of whole digits needs to be reduced. If the MSB is

// set, then increment the exponent and no shift is needed.

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

wire xInf2c, xInf2b;

wire [15:0] xo2;

reg incExpByOne2, incExpByTwo2;

delay #(.WID(1),.DEP(1)) u21 (.clk(clk), .ce(ce), .i(xInf1c), .o(xInf2c));

delay #(.WID(1),.DEP(1)) u22 (.clk(clk), .ce(ce), .i(xInf1b), .o(xInf2b));

delay #(.WID(16),.DEP(2)) u23 (.clk(clk), .ce(ce), .i(xo0), .o(xo2));

delay #(.WID(1),.DEP(2)) u24 (.clk(clk), .ce(ce), .i(under_i), .o(under2));

always @(posedge clk)

        if (ce) incExpByOne2 <= !xInf1a & i1[220];

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

// Clock #3

// - increment exponent

// - detect a zero mantissa

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

wire incExpByOne3;

wire [243:0] i3;

reg [15:0] xo3;

reg zeroMan3;

delay #(.WID(1),.DEP(1)) u32 (.clk(clk), .ce(ce), .i(incExpByOne2), .o(incExpByOne3));

delay #(.WID(244),.DEP(3)) u33 (.clk(clk), .ce(ce), .i(i[243:0]), .o(i3));

wire [15:0] xo2a;

BCDAddN #(.N(4)) ubcdan1

(

        .ci(1'b0),

        .a(xo2),

        .b(16'h0001),

        .o(xo2a),

        .co()

);

always @(posedge clk)

        if (ce) xo3 <= (incExpByOne2 ? xo2a : xo2);

always @(posedge clk)

        if(ce) zeroMan3 <= 1'b0;

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

// Clock #4

// - Shift mantissa left

// - If infinity is reached then set the mantissa to zero

//   shift mantissa left to reduce to a single whole digit

// - create sticky bit

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

reg [115:0] mo4;

reg inexact4;

always @(posedge clk)

if(ce)

casez({zeroMan3,incExpByOne3})

2'b1?:  mo4 <= 1'd0;

2'b01:  mo4 <= {i3[223:112],3'b0,|i3[111:0]};

default:        mo4 <= {i3[219:108],3'b0,|i3[107:0]};

endcase

always @(posedge clk)

if(ce)

casez({zeroMan3,incExpByOne3})

2'b1?:  inexact4 <= 1'd0;

2'b01:  inexact4 <= |i3[111:0];

default:        inexact4 <= |i3[107:0];

endcase

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

// Clock edge #5

// - count leading zeros

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

reg [7:0] leadingZeros5;

wire [15:0] xo5;

wire xInf5;

delay #(.WID(16),.DEP(2)) u51 (.clk(clk), .ce(ce), .i(xo3), .o(xo5));

delay #(.WID(1),.DEP(3)) u52 (.clk(clk), .ce(ce), .i(xInf2c), .o(xInf5) );

/* Lookup table based leading zero count modules give slightly better

   performance but cases must be coded.

generate

begin

if (FPWID <= 32) begin

cntlz32Reg clz0 (.clk(clk), .ce(ce), .i({mo4,4'b0}), .o(leadingZeros5) );

assign leadingZeros5[7:6] = 2'b00;

end

else if (FPWID<=64) begin

assign leadingZeros5[7] = 1'b0;

cntlz64Reg clz0 (.clk(clk), .ce(ce), .i({mo4,7'h0}), .o(leadingZeros5) );

end

else if (FPWID<=80) begin

assign leadingZeros5[7] = 1'b0;

cntlz80Reg clz0 (.clk(clk), .ce(ce), .i({mo4,11'b0}), .o(leadingZeros5) );

end

else if (FPWID<=84) begin

assign leadingZeros5[7] = 1'b0;

cntlz96Reg clz0 (.clk(clk), .ce(ce), .i({mo4,23'b0}), .o(leadingZeros5) );

end

else if (FPWID<=96) begin

assign leadingZeros5[7] = 1'b0;

cntlz96Reg clz0 (.clk(clk), .ce(ce), .i({mo4,11'b0}), .o(leadingZeros5) );

end

else if (FPWID<=128)

cntlz128Reg clz0 (.clk(clk), .ce(ce), .i({mo4,11'b0}), .o(leadingZeros5) );

end

endgenerate

*/

// Sideways add.

// Normally there would be only one to two leading zeros. It is tempting then

// to check for only one or two. But, denormalized numbers might have more

// leading zeros. If denormals were not supported this could be made smaller

// and faster.

`ifdef SUPPORT_DENORMALS

reg [7:0] lzc;

reg got_one;

always @*

begin

  got_one = 1'b0;

  lzc = 8'h00;

  for (n = 115; n >= 0; n = n - 4) begin

    if (!got_one) begin

      if (mo4[n]|mo4[n-1]|mo4[n-2]|mo4[n-3])

        got_one = 1'b1;

      else

        lzc = lzc + 1'b1;

    end

  end

end

always @(posedge clk)

  if (ce) leadingZeros5 <= lzc;

`else

always @(posedge clk)

if (ce)

casez(mo4[111:103])

8'h00000000:    leadingZeros5 <= 8'd2;

8'h0000????:    leadingZeros5 <= 8'd1;

default:                        leadingZeros5 <= 8'd0;

endcase

`endif

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

// Clock edge #6

// - Compute how much we want to decrement exponent by

// - compute amount to shift left and right

// - at infinity the exponent can't be incremented, so we can't shift right

//   otherwise it was an underflow situation so the exponent was negative

//   shift amount needs to be negated for shift register

// If the exponent underflowed, then the shift direction must be to the

// right regardless of mantissa bits; the number is denormalized.

// Otherwise the shift direction must be to the left.

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

reg [7:0] lshiftAmt6;

reg [7:0] rshiftAmt6;

wire rightOrLeft6;      // 0=left,1=right

wire xInf6;

wire [15:0] xo6;

wire [115:0] mo6;

wire zeroMan6;

vtdl #(1) u61 (.clk(clk), .ce(ce), .a(4'd5), .d(under_i), .q(rightOrLeft6) );

delay #(.WID(16),.DEP(1)) u62 (.clk(clk), .ce(ce), .i(xo5), .o(xo6));

delay #(.WID(116),.DEP(2)) u63 (.clk(clk), .ce(ce), .i(mo4), .o(mo6) );

delay #(.WID(1),.DEP(1)) u64 (.clk(clk), .ce(ce), .i(xInf5), .o(xInf6) );

delay #(.WID(1),.DEP(3)) u65 (.clk(clk), .ce(ce),  .i(zeroMan3), .o(zeroMan6));

delay #(.WID(1),.DEP(5)) u66 (.clk(clk), .ce(ce), .i(sx0), .o(sx5) );

wire [13:0] xo5d = xo5[3:0] + xo5[7:4] * 10 + xo5[11:8] * 100 + xo5[15:12] * 1000;

always @(posedge clk)

        if (ce) lshiftAmt6 <= {leadingZeros5 > xo5d ? xo5d : leadingZeros5,2'b0};

always @(posedge clk)

        if (ce) rshiftAmt6 <= xInf5 ? 1'd0 : sx5 ? 1'd0 : xo5d > 14'd24 ? 8'd96 : {xo5d[5:0],2'b00}; // xo2 is negative !

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

// Clock edge #7

// - figure exponent

// - shift mantissa

// - figure sticky bit

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

reg [15:0] xo7;

wire rightOrLeft7;

reg [115:0] mo7l, mo7r;

reg St6,St7;

delay #(.WID(1),.DEP(1)) u71 (.clk(clk), .ce(ce), .i(rightOrLeft6), .o(rightOrLeft7));

wire [11:0] lshftAmtBCD;

wire [15:0] xo7d;

BinToBCD ubbcd1 (lshiftAmt6, lshftAmtBCD);

BCDSubN #(.N(4)) ubcdsn1

(

        .ci(1'b0),

        .a(xo6),

        .b({4'h0,lshftAmtBCD}),

        .o(xo7d),

        .co()

);

always @(posedge clk)

if (ce)

        xo7 <= zeroMan6 ? xo6 :

                xInf6 ? xo6 :                                   // an infinite exponent is either a NaN or infinity; no need to change

                rightOrLeft6 ? 1'd0 :   // on a right shift, the exponent was negative, it's being made to zero

                xo7d;                   // on a left shift, the exponent can't be decremented below zero

always @(posedge clk)

        if (ce) mo7r <= mo6 >> rshiftAmt6;

always @(posedge clk)

        if (ce) mo7l <= mo6 << lshiftAmt6;

// The sticky bit is set if the bits shifted out on a right shift are set.

always @*

begin

  St6 = 1'b0;

  for (n = 0; n < 116; n = n + 1)

    if (n <= rshiftAmt6 + 1) St6 = St6|mo6[n];

end

always @(posedge clk)

  if (ce) St7 <= St6;

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

// Clock edge #8

// - select mantissa

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

wire so,sxo,nano,info;

wire [15:0] xo;

reg [115:0] mo;

vtdl #(1) u81 (.clk(clk), .ce(ce), .a(4'd7), .d(so0), .q(so) );

delay #(.WID(16),.DEP(1)) u82 (.clk(clk), .ce(ce), .i(xo7), .o(xo));

vtdl #(.WID(1)) u83 (.clk(clk), .ce(ce), .a(4'd3), .d(inexact4), .q(inexact_o));

delay #(.WID(1),.DEP(1)) u84 (.clk(clk), .ce(ce), .i(rightOrLeft7), .o(under_o));

vtdl #(1) u85 (.clk(clk), .ce(ce), .a(4'd7), .d(sx0), .q(sxo) );

vtdl #(1) u86 (.clk(clk), .ce(ce), .a(4'd7), .d(nan0), .q(nano) );

vtdl #(1) u87 (.clk(clk), .ce(ce), .a(4'd7), .d(inf0), .q(info) );

always @(posedge clk)

        if (ce) mo <= rightOrLeft7 ? mo7r|{St7,4'b0} : mo7l;

assign o = {nano,so,info,sxo,xo,mo[115:4]};

endmodule