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

//        __

//   \\__/ o\    (C) 2006-2016  Robert Finch, Waterloo

//    \  __ /    All rights reserved.

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

//       ||

//

//      i2f.v

//  - convert integer to floating point

//  - parameterized width

//  - IEEE 754 representation

//  - pipelineable

//  - single cycle latency

//

// 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/>.    

//                                                                          

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

module i2f

#(      parameter WID = 32)

(

        input clk,

        input ce,

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

        input [WID-1:0] i,               // integer input

        output [WID-1:0] o               // float output

);

localparam MSB = WID-1;

localparam EMSB = WID==128 ? 14 :

                  WID==96 ? 14 :

                  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==128 ? 111 :

                  WID==96 ? 79 :

                  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;

wire [EMSB:0] zeroXp = {EMSB{1'b1}};

wire iz;                        // zero input ?

wire [MSB:0] imag;       // get magnitude of i

wire [MSB:0] imag1 = i[MSB] ? -i : i;

wire [7:0] lz;           // count the leading zeros in the number

wire [EMSB:0] wd;        // compute number of whole digits

wire so;                        // copy the sign of the input (easy)

wire [2:0] rmd;

delay1 #(3)   u0 (.clk(clk), .ce(ce), .i(rm),     .o(rmd) );

delay1 #(1)   u1 (.clk(clk), .ce(ce), .i(i==0),   .o(iz) );

delay1 #(WID) u2 (.clk(clk), .ce(ce), .i(imag1),  .o(imag) );

delay1 #(1)   u3 (.clk(clk), .ce(ce), .i(i[MSB]), .o(so) );

generate

if (WID==128) begin

cntlz128Reg    u4 (.clk(clk), .ce(ce), .i(imag1), .o(lz) );

end else if (WID==96) begin

cntlz96Reg    u4 (.clk(clk), .ce(ce), .i(imag1), .o(lz) );

end else if (WID==80) begin

cntlz80Reg    u4 (.clk(clk), .ce(ce), .i(imag1), .o(lz) );

end else if (WID==64) begin

cntlz64Reg    u4 (.clk(clk), .ce(ce), .i(imag1), .o(lz) );

end else begin

cntlz32Reg    u4 (.clk(clk), .ce(ce), .i(imag1), .o(lz) );

assign lz[6]=1'b0;

end

endgenerate

assign wd = zeroXp - 1 + WID - lz;      // constant except for lz

wire [EMSB:0] xo = iz ? 0 : wd;

wire [MSB:0] simag = imag << lz;         // left align number

wire g =  simag[EMSB+2];        // guard bit (lsb)

wire r =  simag[EMSB+1];        // rounding bit

wire s = |simag[EMSB:0]; // "sticky" bit

reg rnd;

// Compute the round bit

always @(rmd,g,r,s,so)

        case (rmd)

        3'd0:   rnd = (g & r) | (r & s);        // round to nearest even

        3'd1:   rnd = 0;                                 // round to zero (truncate)

        3'd2:   rnd = (r | s) & !so;            // round towards +infinity

        3'd3:   rnd = (r | s) & so;                     // round towards -infinity

        3'd4:   rnd = (r | s);

        endcase

// "hide" the leading one bit = MSB-1

// round the result

wire [FMSB:0] mo = simag[MSB-1:EMSB+1]+rnd;

assign o = {so,xo,mo};

endmodule

module i2f_tb();

reg clk;

reg [7:0] cnt;

wire [31:0] fo;

reg [31:0] i;

initial begin

clk = 1'b0;

cnt = 0;

end

always #10 clk=!clk;

always @(posedge clk)

        cnt = cnt + 1;

always @(cnt)

case(cnt)

8'd0:   i <= 32'd0;

8'd1:   i <= 32'd16777226;

endcase

i2f #(32) u1 (.clk(clk), .ce(1), .rm(2'd0), .i(i), .o(fo) );

i2f #(80) u2 (.clk(clk), .ce(1), .rm(2'd0), .i(i), .o(fo) );

endmodule