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// +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

//

// This file is part of the M32632 project

// http://opencores.org/project,m32632

//

// Filename: SP_FPU.v

// Version:  1.0

// Date:     30 May 2015

//

// Copyright (C) 2015 Udo Moeller

// 

// This source file may be used and distributed without 

// restriction provided that this copyright statement is not 

// removed from the file and that any derivative work contains 

// the original copyright notice and the associated disclaimer.

// 

// 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 2.1 of the License, or (at your option) any 

// later version. 

// 

// This source 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 Lesser General Public License for more 

// details. 

// 

// You should have received a copy of the GNU Lesser General 

// Public License along with this source; if not, download it 

// from http://www.opencores.org/lgpl.shtml 

// 

// +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

//

//      Modules contained in this file:

//      1. ADDSUB               Adder and Subtractor for 36 bit

//      2. SFPU_ADDSUB  Single Precision Floating Point Adder/Subtractor and Converter

//      3. SFPU_MUL             Single Precision Floating Point Multiplier

//      4. SP_FPU               Top Level of Single Precision Floating Point Unit

//

// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

//

//      1. ADDSUB               Adder and Subtractor for 36 bit

//

// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

module ADDSUB (dataa, datab, add_sub, result);

        input   [35:0]   dataa,datab;

        input                   add_sub;        // 1 = Addition , 0 = Subtraction

        output  [35:0]   result;

        assign result = dataa + (add_sub ? datab : ~datab) + {35'd0,~add_sub};

endmodule

// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

//

//      2. SFPU_ADDSUB  Single Precision Floating Point Adder/Subtractor and Converter

//

// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

module SFPU_ADDSUB ( SRC1, SRC2, NZEXP, BWD, SELECT, OUT, IOUT, CMPRES );

        input   [31:0]   SRC1,SRC2;      // Input data

        input    [2:1]  NZEXP;

        input    [1:0]   BWD;            // size of integer

        input    [3:0]   SELECT;

        output  [36:0]   OUT;            // the result

        output  [31:0]   IOUT;           // result of ROUNDFi/TRUNCFi/FLOORFi

        output   [1:0]   CMPRES;

        // ++++++++++++++++++++++++++++++++++

        // MOViF : 1. step

        reg  [31:8]     movdat;

        wire [31:0]      movif;

        always @(BWD or SRC1)

                casex({BWD,SRC1[15],SRC1[7]})

                  4'b00x0 : movdat =  24'h0000_00;                              // Byte

                  4'b00x1 : movdat =  24'hFFFF_FF;

                  4'b010x : movdat = {16'h0000,SRC1[15:8]};             // Word

                  4'b011x : movdat = {16'hFFFF,SRC1[15:8]};

                default   : movdat = SRC1[31:8];                                // Double

                endcase

        assign movif = movdat[31] ? (32'h0 - {movdat,SRC1[7:0]}) : {movdat,SRC1[7:0]};

                                                                // -2^31 is kept

        // ROUNDFi/TRUNCFi/FLOORFi : 1. step

        reg                     ovflag,ovflag2;

        wire [8:0]       rexdiff,rexo;

        wire            rovfl,minint;

        wire            ganzklein;      // Flag for 0

        assign rexdiff = 9'h09D - {1'b0,SRC1[30:23]};   // 4..0 is the right shift value

        assign rovfl = (ovflag | ovflag2) & (SELECT[1:0] == 2'b11) & ~minint;

        assign ganzklein = (~rexdiff[8] & (rexdiff[7:5] != 3'b000));    // 0 is implicit via SRC1[30:23]=0

        // Detection of Overflow

        assign rexo = ({1'b0,SRC1[30:23]} - {8'h3F,~BWD[1]});   // subtract B/W = 7F , D = 7E

        always @(BWD or rexo)

                casex (BWD)

                  2'b00 : ovflag = (~rexo[8] & (rexo[7:3] != 5'h0));    // Exponent 0..7 because of -128.4 => -128

                  2'b01 : ovflag = (~rexo[8] & (rexo[7:4] != 4'h0));    // Exponent 0..15 because of -128.4 => -128

                default : ovflag = (~rexo[8] & (rexo[7:5] != 3'h0));    // Exponent only 0..30 

                endcase

        assign minint = (SRC1 == 32'hCF00_0000) & BWD[1];       // detection of -2^31

        // ++++++++++++++++++++++++++++++++++

        // ADD/SUB : 1. step : which operand ist bigger ? if required exchange

        // SUB/CMP : SRC2 - SRC1

        wire  [8:0]      exdiff;

        wire [23:0]      madiff;

        wire            switch,sign,sign1,sign2;

        wire            variante;

        wire            vorz,addflag;

        wire [35:0]      result_sw,result_nosw;

        wire [24:0] value1,value2;

        wire [35:0] result;

        assign exdiff = {1'b0,SRC2[30:23]} - {1'b0,SRC1[30:23]};        // Difference of Exponents

        assign madiff = {1'b0,SRC2[22:0]}  - {1'b0,SRC1[22:0]};           // Difference of Mantissas

        // if exdiff = 0 the shifter to the right is not needed ! 

        assign variante = (exdiff[8:1] == 8'h00) | (exdiff == 9'h1FF) | SELECT[1];      // MUX at the end, ROUND/TRUNC/MOViF uses case 1

// ++++++++++++++++++++++++++  1. case works on MOViF  +++++++++++++++++++++++++++++++++++++++

        assign switch = exdiff[8] | ((exdiff[7:0] == 8'h0) & madiff[23]);        // exchange ?

        assign value1 = exdiff[0] ? {1'b0,NZEXP[1],SRC1[22:0]} : {NZEXP[1],SRC1[22:0],1'b0};

        assign value2 = exdiff[0] ? {1'b0,NZEXP[2],SRC2[22:0]} : {NZEXP[2],SRC2[22:0],1'b0};

        // The Subtraction needs 3 Guard-Bits after LSB for rounding ! 36 Bit wide

        //                                                                                              1

        ADDSUB  addsub_nosw     (.dataa({1'b0,SRC2[30:23],NZEXP[2],SRC2[22:0],3'b000}),

                                                 .datab({9'h0,value1,2'b0}), .add_sub(addflag),

                                                 .result(result_nosw) );

        ADDSUB  addsub_sw       (.dataa({1'b0,SRC1[30:23],NZEXP[1],SRC1[22:0],3'b000}),

                                                 .datab({9'h0,value2,2'b0}), .add_sub(addflag),

                                                 .result(result_sw) );

        assign result = switch ? result_sw : result_nosw;

        //      SRC2   SRC1     : switch = 0            SRC2   SRC1 : switch = 1

        //        5  +   3  : +(5 + 3) =  8               3  +   5  : +(5 + 3) =  8             SELECT[0] = 0

        //        5  + (-3) : +(5 - 3) =  2               3  + (-5) : -(5 - 3) = -2

        //      (-5) +   3  : -(5 - 3) = -2             (-3) +   5  : +(5 - 3) =  2

        //      (-5) + (-3) : -(5 + 3) = -8             (-3) + (-5) : -(5 + 3) = -8

        //        5  -   3  : +(5 - 3) =  2               3  -   5  : -(5 - 3) = -2             SELECT[0] = 1

        //        5  - (-3) : +(5 + 3) =  8               3  - (-5) : +(5 + 3) =  8

        //      (-5) -   3  : -(5 + 3) = -8             (-3) -   5  : -(5 + 3) = -8

        //      (-5) - (-3) : -(5 - 3) = -2             (-3) - (-5) : +(5 - 3) =  2

        assign sign1 = SRC1[31];

        assign sign2 = SRC2[31];

        assign vorz    = switch ? (SELECT[0] ^ sign1) : sign2;

        assign addflag = ~(SELECT[0] ^ (sign1 ^ sign2));

        // CMPF : 1. step : what happend if Invalid Operand occurs - no Flag update !

        assign CMPRES[1] = ~CMPRES[0] & (switch ? ~sign1 : sign2);               // see table above : N-Bit=1 if SRC1 > SRC2

        assign CMPRES[0] = (SRC1 == SRC2) | (~NZEXP[2] & ~NZEXP[1]);     // Z-Bit : SRC1=SRC2, +0.0 = -0.0

        // ++++++++++++++++++++++++++++++++++

        // ADD/SUB : 3. step : prepare of Barrelshifter Left

        wire [31:0] blshift;

        wire  [9:0]      shiftl;

        wire            shift_16;

        wire [33:0] add_q;

        wire [31:0]      muxsrc2;

        wire  [1:0] inex;

        assign blshift = SELECT[1] ? movif : {result[26:0],5'h00};       // Feeding of MOViF

        assign shiftl = SELECT[1] ? 10'h09E : {1'b0,result[35:27]};      // MOViF

        assign shift_16 = (blshift[31:16] == 16'h0000);

        // In case of ADD the result bypasses the Barrelshifter left

        assign add_q = (muxsrc2[24] != result[27]) ? {result[35:3],(result[2:0] != 3'b000)}

                                                                                           : {result[35:27],result[25:2],(result[1:0] != 2'b00)} ;

        // ++++++++++++++++++++++++++++++++++

        // ADD/SUB : 4. step : Barrelshifter left for SUB and MOViF :

        wire            shift_8,shift_4,shift_2,shift_1,zero;

        wire  [1:0] lsb_bl;

        wire [31:0]      blshifta,blshiftb,blshiftc,blshiftd,blshifte;

        wire  [9:0]      expol;

        wire [36:0] out_v1;

        assign blshifta = shift_16 ? {blshift[15:0],16'h0000}    : blshift;

        assign shift_8 = (blshifta[31:24] == 8'h00);

        assign blshiftb = shift_8  ? {blshifta[23:0],8'h00}      : blshifta;

        assign shift_4 = (blshiftb[31:28] == 4'h0);

        assign blshiftc = shift_4  ? {blshiftb[27:0],4'h0}               : blshiftb;

        assign shift_2 = (blshiftc[31:30] == 2'b00);

        assign blshiftd = shift_2  ? {blshiftc[29:0],2'b00}      : blshiftc;

        assign shift_1 = ~blshiftd[31];

        assign blshifte = shift_1  ? {blshiftd[30:0],1'b0}               : blshiftd;

        // Overflow at ROUNDFi/TRUNCFi/FLOORFi via overflow in exponent shown, SELECT[1] is then 1 !

        assign expol = (shiftl - {5'h00,shift_16,shift_8,shift_4,shift_2,shift_1}) | {1'b0,rovfl,8'h00};

        // Inexact at ROUNDFi/TRUNCFi/FLOORFi : evaluation for all one level higher

        assign lsb_bl = (SELECT[1:0] == 2'b11) ? inex : {blshifte[7],(blshifte[6:0] != 7'h00)};

        assign zero =  (~SELECT[1] & ~NZEXP[2] & ~NZEXP[1])

                                 | ((blshift == 32'h0) & ((~addflag & ~SELECT[1]) | (SELECT[1:0] == 2'b10)));

        assign sign = SELECT[1] ? movdat[31] : vorz;

        assign out_v1 = (addflag & ~SELECT[1]) ? {zero,sign,1'b0,add_q}

                                                                                   : {zero,sign,expol,blshifte[30:8],lsb_bl};

// +++++++++++++++++++++++++  2. case works on ROUND/TRUNC/FLOOR  ++++++++++++++++++++++++++++++++++

        wire            vswitch;

        wire  [4:0]      shift1,shift2;

        wire  [8:0]      exdiff12;

        wire [23:0]      muxsrc1;

        wire [32:9]     pipe1;  // numbering special for Right Shifter

        wire  [4:0]      shift;

// the difference between SRC1 and SRC2 is bigger/equal 4:1 => no Barrelshifter after ADDSUB neccessary

        assign vswitch = exdiff[8];     // exchange ?

        assign shift1 = (exdiff[7:5] != 3'h0) ? 5'h1F : exdiff[4:0];

        assign exdiff12 = {1'b0,SRC1[30:23]} - {1'b0,SRC2[30:23]};      // caclulate already

        assign shift2 = (exdiff12[7:5] != 3'h0) ? 5'h1F : exdiff12[4:0];

        assign muxsrc2 = vswitch ? {SRC1[30:23],1'b1,SRC1[22:0]} : {SRC2[30:23],1'b1,SRC2[22:0]}; // Including exponent

        assign muxsrc1 = vswitch ? {NZEXP[2],SRC2[22:0]} : {NZEXP[1],SRC1[22:0]};

        assign pipe1 = SELECT[1] ? (ganzklein ? 24'h0 : {NZEXP[1],SRC1[22:0]}) : muxsrc1;        // Feeding in R.T.F.

        assign shift = SELECT[1] ? rexdiff[4:0] : (vswitch ? shift2 : shift1);

        // ++++++++++++++++++++++++++++++++++

        // ADD/SUB + ROUND/TRUNC/FLOOR : 2. step : Barrelshifter to right -->

        wire [32:0] brshifta,brshiftb,brshiftc,brshiftd;

        wire [32:0] brshifte;    // last stage

        // 33322222222221111111111

        // 2109876543210987654321098765432-10

        // 1VVVVVVVVVVVVVVVVVVVVVVV0000000-00   // last 2 Bit for rounding

        assign brshifta = shift[4] ? {16'h0,pipe1[32:17],  (pipe1[16:9]   != 8'h00)}  : {pipe1,9'h0};

        assign brshiftb = shift[3] ? { 8'h0,brshifta[32:9],(brshifta[8:0] != 9'h000)} : brshifta;

        assign brshiftc = shift[2] ? { 4'h0,brshiftb[32:5],(brshiftb[4:0] != 5'h00)}  : brshiftb;

        assign brshiftd = shift[1] ? { 2'h0,brshiftc[32:3],(brshiftc[2:0] != 3'h0)}   : brshiftc;

        assign brshifte = shift[0] ? { 1'b0,brshiftd[32:2],(brshiftd[1:0] != 2'h0)}   : brshiftd;

        // ++++++++++++++++++++++++++++++++++

        // ROUNDFi/TRUNCFi/FLOORFi : 3. step : round to integer

        reg                     car_ry;

        wire [30:0] compl;

        wire [31:0] iadder;

        assign inex = brshifte[1:0];             // Inexact-Flag-Data via multiplexer at the end

        always @(SELECT or sign1 or brshifte or inex or ganzklein)

                casex (SELECT[3:2])

                    2'b00 : car_ry = sign1 ^ ((brshifte[2:0] == 3'b110) | (inex == 2'b11));      // ROUNDLi

                    2'b1x : car_ry = sign1 ? (~ganzklein & (inex == 2'b00)) : 1'b0;     // +numbers like TRUNCLi, -numbers round to "-infinity"

                  default : car_ry = sign1;     // TRUNCLi , simple cut

                endcase

        assign compl  = sign1 ? ~brshifte[32:2] : brshifte[32:2];

        assign iadder = {sign1,compl} + {31'h0,car_ry};

        assign IOUT = minint ? 32'h8000_0000 : iadder;

        always @(iadder or BWD or sign1)        // special overflow detection i.e. -129 bis -255 bei Byte

                casex (BWD)                                             // or 127.9 -> 128 = Fehler !

                  2'b00 : ovflag2 = (iadder[8]  != iadder[7]);  // Byte

                  2'b01 : ovflag2 = (iadder[16] != iadder[15]); // Word

                default : ovflag2 = 1'b0;

                endcase

        // ++++++++++++++++++++++++++++++++++

        // only ADD/SUB : 3. step : Add or Subtract

        // the modul ADDSUB integrates the carry from the mantissa : 35 Bit

        wire            lsb;

        wire [35:0]      vresult;

        wire  [7:0]      eminus1;

        wire [33:0] vadd_q,vsub_q;

        wire            vzero;

        wire [36:0] out_v0;

        assign lsb = (brshifte[6:0] != 7'h00);

        // Adder-Definition : "0"(8 Bit Exponent)"1"(23 Bit Mantissa)"000"

        ADDSUB  addsub_v        (.dataa({1'b0,muxsrc2,3'b000}),

                                                 .datab({9'h0,brshifte[32:7],lsb}), .add_sub(addflag),

                                                 .result(vresult) );

        assign eminus1 = muxsrc2[31:24] - 8'h01;        // a greater Underflow can not exist, because minimal Exponent = 0..01

        // Case ADD : Bit 23 : LSB of exponent

        assign vadd_q = (muxsrc2[24] != vresult[27]) ? {vresult[35:3],(vresult[2:0] != 3'b000)}

                                                                                                 : {vresult[35:27],vresult[25:2],(vresult[1:0] != 2'b00)} ;

        // Case SUB : Bit 26 : "hidden" MSB of mantissa

        assign vsub_q = vresult[26] ? {vresult[35:27],     vresult[25:2],(vresult[1:0] != 2'b00)}        // like the vadd_q "0" case

                                                            : {vresult[35],eminus1,vresult[24:0]} ;

        // SELECT[1] has here no meaning

        assign vzero = (vresult[26:0] == 27'h0) & ~addflag;      // only if "-" can be the result 0

        assign out_v0 = addflag ? {vzero,vorz,1'b0,vadd_q}

                                                        : {vzero,vorz,1'b0,vsub_q} ;

        assign OUT = variante ? out_v1 : out_v0;        // Last multiplexer

endmodule

// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

//

//      3. SFPU_MUL             Single Precision Floating Point Multiplier

//

// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

module SFPU_MUL ( SRC1, SRC2, MRESULT, NZEXP, OUT);

        input   [31:0]   SRC1,SRC2;      // only exponent of input data used

        input   [47:0]   MRESULT;

        input    [2:1]  NZEXP;          // Flags of input data

        output  [36:0]   OUT;            // The result

        wire  [9:0] exponent,expoh,expol;

        wire  [1:0] restlow,resthigh;

        wire            zero,sign,orlow;

        assign zero =   ~NZEXP[2] | ~NZEXP[1];  // one of both NULL -> NULL is the result

        assign sign =   (SRC1[31] ^ SRC2[31]) & ~zero;

        assign orlow =  (MRESULT[21:0] != 22'b0);

        assign restlow  = {MRESULT[22],orlow};

        assign resthigh = {MRESULT[23],(MRESULT[22] | orlow)};

        assign exponent = {2'b00,SRC1[30:23]} + {2'b00,SRC2[30:23]};

        assign expoh    = exponent - 10'h07E;

        assign expol    = exponent - 10'h07F;    // for MSB if MRESULT=0

        assign OUT = MRESULT[47] ? {zero,sign,expoh,MRESULT[46:24],resthigh}

                                                         : {zero,sign,expol,MRESULT[45:23],restlow};

endmodule

// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

//

//      4. SP_FPU               Top Level of Single Precision Floating Point Unit

//

// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

module SP_FPU (BCLK, OPCODE, SRC1, SRC2, FSR, MRESULT, BWD, FL, FP_OUT, I_OUT, TT_SP, SP_CMP, SP_MUX, LD_FSR, UP_SP);

        input                   BCLK;           // is not used !

        input    [7:0]   OPCODE;

        input   [31:0]   SRC1,SRC2;      // Input data

        input    [8:3]  FSR;            // Floating Point Status Register

        input   [47:0]   MRESULT;        // Multiplier result

        input    [1:0]   BWD;            // Size of integer

        input                   FL;

        output  [31:0]   FP_OUT,I_OUT;   // The results

        output   [4:0]   TT_SP;          // Trap-Type

        output   [2:0]   SP_CMP;         // CMPF result

        output                  SP_MUX,LD_FSR,UP_SP;

        reg              [2:0]   tt;

        reg              [3:0]   select;

        reg                             car_ry;

        wire    [36:0]   mulout,addout,fpout;

        wire     [2:1]  nzexp;

        wire    [34:2]  rund;           // Indexnumbers like xxxout

        wire                    overflow,underflow,inexact;

        wire                    op_cmp;

        wire                    nan,nan_1,nan_2;

        // Control of datapath 

        always @(OPCODE)

                casex (OPCODE)

                  8'b1011_0000 : select = 4'b1000;      // 0 0 0 :      ADDF    Shifter are reused

                  8'b1011_0100 : select = 4'b1001;      // 0 0 1 :      SUBF

                  8'b1001_000x : select = 4'b1010;      // 0 1 0 :      MOViF

                  8'b1001_100x : select = 4'b1011;      // 0 1 1 :      ROUNDFi

                  8'b1001_101x : select = 4'b1011;      // 0 1 1 :      TRUNCFi

                  8'b1001_111x : select = 4'b1011;      // 0 1 1 :      FLOORFi

                  8'b1011_0010 : select = 4'b1001;      // 0 0 1 :      CMPF

                  8'b1011_1100 : select = 4'b1100;      // 1 x x :      MULF

                  default      : select = 4'b0;

                endcase

        assign SP_MUX = select[3] & (select[1:0] != 2'b11) & FL; // Output multiplexer

        assign LD_FSR = (OPCODE[7:4] == 4'h9) & (OPCODE[3:1] == 3'b001);        // LFSR does only Double (according datasheet NS32016)

        assign UP_SP  = select[3] & FL;                         // All FPU opcodes of SP_FPU

        assign op_cmp = (OPCODE == 8'hB2) & FL;

        // SRCFLAGS

        assign nzexp[2] = (SRC2[30:23] != 8'd0);                // only exponent 0 ,denormalized Number => NAN !

        assign nzexp[1] = (SRC1[30:23] != 8'd0);                // only exponent 0 ,denormalized Number => NAN !

        assign nan_2    = (SRC2[30:23] == 8'hFF) | (~nzexp[2] & (SRC2[22:0] != 23'd0));  // NAN

        assign nan_1    = (SRC1[30:23] == 8'hFF) | (~nzexp[1] & (SRC1[22:0] != 23'd0));  // NAN

        assign nan = (select[1:0] == 2'b11) ? nan_1 : (~select[1] & (nan_2 | nan_1));

        // 001 : ADDF,... + 011 : CMPF

        SFPU_ADDSUB IADDSUB     ( .SRC1(SRC1), .SRC2(SRC2), .NZEXP(nzexp), .BWD(BWD),

                                                  .SELECT({OPCODE[2:1],select[1:0]}), .OUT(addout), .IOUT(I_OUT), .CMPRES(SP_CMP[1:0]) );

        // 100 : MULF

        SFPU_MUL IMUL ( .SRC1(SRC1), .SRC2(SRC2), .MRESULT(MRESULT), .OUT(mulout), .NZEXP(nzexp) );

        // FP - Pfad : selection of result and rounding :

        assign fpout = (OPCODE[5] & OPCODE[3]) ? mulout : addout;

        always @(FSR or fpout)  // calculate Carry according rounding mode, fpout[35] = sign bit

                casex (FSR[8:7])

                  2'b00 : car_ry = ((fpout[1:0] == 2'b10) & fpout[2]) | (fpout[1:0] == 2'b11);    // round to nearest

                  2'b10 : car_ry = ~fpout[35] & (fpout[1:0] != 2'b00);   // round to positiv infinity

                  2'b11 : car_ry =  fpout[35] & (fpout[1:0] != 2'b00);   // round to negativ infinity

                default : car_ry = 1'b0;                                                                // round to zero

                endcase

        assign rund = {fpout[34:2]} + {32'h0,car_ry};

        // Detection of Overflow, Underflow and Inexact : epxonent is [34:25] = 10 Bits

        assign overflow  = ~rund[34] & (rund[33] | (rund[32:25] == 8'hFF));

        assign underflow = (rund[34] | (rund[33:25] == 9'h0)) & ~fpout[36];     // Zero-Flag

        assign inexact   = (fpout[1:0] != 2'b00);

        // CMPF can have no other error except NAN 

        always @(nan or op_cmp or overflow or underflow or inexact or FSR)

                casex ({nan,op_cmp,overflow,FSR[3],underflow,FSR[5],inexact})

                        7'b1xxxxxx : tt = 3'b101;       // Invalid operation

                        7'b001xxxx : tt = 3'b010;       // Overflow

                        7'b00011xx : tt = 3'b001;       // Underflow

                        7'b0000011 : tt = 3'b110;       // Inexact Result

                        default    : tt = 3'b000;       // no error

                endcase

        assign TT_SP = {(inexact & ~op_cmp),(underflow & ~op_cmp),tt};

        assign SP_CMP[2] = nan;

        // Underflow Special case and force ZERO 

        assign FP_OUT = (underflow | fpout[36]) ? 32'd0 : {fpout[35],rund[32:2]};

endmodule