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

//        __

//   \\__/ o\    (C) 2007-2016  Robert Finch, Stratford

//    \  __ /    All rights reserved.

//     \/_//     robfinch<remove>@finitron.ca

//       ||

//

// 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 <http://www.gnu.org/licenses/>.    

//

//      fpCompare.v

//  - floating point comparison unit

//  - parameterized width

//  - IEEE 754 representation

//

// Compares two fgloating point numbers and returns a status output.

// Bit:

// 0:   1 = equal, 0=not equal

// 1:   1 = less than,

// 2:   1 = magnitude less than

// 3:   1 = unordered (nan in compare)

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

//

module fpCompare(a, b, o, nanx);

parameter WID = 32;

localparam MSB = WID-1;

localparam EMSB = WID==80 ? 14 :

                  WID==64 ? 10 :

                                  WID==52 ? 10 :

                                  WID==48 ? 10 :

                                  WID==44 ? 10 :

                                  WID==42 ? 10 :

                                  WID==40 ?  9 :

                                  WID==32 ?  7 :

                                  WID==24 ?  6 : 4;

localparam FMSB = WID==80 ? 63 :

                  WID==64 ? 51 :

                                  WID==52 ? 39 :

                                  WID==48 ? 35 :

                                  WID==44 ? 31 :

                                  WID==42 ? 29 :

                                  WID==40 ? 28 :

                                  WID==32 ? 22 :

                                  WID==24 ? 15 : 9;

input [WID-1:0] a, b;

output [3:0] o;

reg [3:0] o;

output nanx;

// Decompose the operands

wire sa;

wire sb;

wire [EMSB:0] xa;

wire [EMSB:0] xb;

wire [FMSB:0] ma;

wire [FMSB:0] mb;

wire az, bz;

wire nan_a, nan_b;

fpDecompose #(WID) u1(.i(a), .sgn(sa), .exp(xa), .man(ma), .fract(), .xz(), .mz(), .vz(az), .inf(), .xinf(), .qnan(), .snan(), .nan(nan_a) );

fpDecompose #(WID) u2(.i(b), .sgn(sb), .exp(xb), .man(mb), .fract(), .xz(), .mz(), .vz(bz), .inf(), .xinf(), .qnan(), .snan(), .nan(nan_b) );

wire unordered = nan_a | nan_b;

wire eq = (az & bz) || (a==b);  // special test for zero

wire gt1 = {xa,ma} > {xb,mb};

wire lt1 = {xa,ma} < {xb,mb};

wire lt = sa ^ sb ? sa & !(az & bz): sa ? gt1 : lt1;

always @(unordered or eq or lt)

begin

        o[0] = eq;

        o[1] = lt;

        o[2] = lt1;

        o[3] = unordered;

end

// an unorder comparison will signal a nan exception

//assign nanx = op!=`FCOR && op!=`FCUN && unordered;

assign nanx = 1'b0;

endmodule

module fpCompare_tb();

wire [3:0] o1,o2,o3,o4;

fpCompare #(32) u1 (.a(32'h80000000), .b(32'h00000000), .o(o1), .nanx() );  // -0 to +0

fpCompare #(32) u2 (.a(32'h3F800000), .b(32'hBF800000), .o(o2), .nanx() );  // 1 to -1

fpCompare #(32) u3 (.a(32'hC1200000), .b(32'h41C80000), .o(o3), .nanx() );  // -10 to 25

fpCompare #(32) u4 (.a(32'h42C80000), .b(32'h43520000), .o(o4), .nanx() );  // 100 to 210

endmodule