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

//        __

//   \\__/ o\    (C) 2017-2019  Robert Finch, Waterloo

//    \  __ /    All rights reserved.

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

//       ||

//

//      sigmoid.v

//              - perform sigmoid function

//

//

// 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/>.    

//

//

// This module returns the sigmoid of a number using a lookup table.

// -1.0 or +1.0 is returned for entries outside of the range -8.0 to +8.0

//                                                                          

// ToTo: check pipelining of values

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

`define ONE80                                   80'h3FFF0000000000000000

`define EIGHT80                         80'h40020000000000000000

`define FIVETWELVE80    80'h40080000000000000000

`define ONE64                                   64'h3FF0000000000000

`define EIGHT64                         64'h4020000000000000

`define FIVETWELVE64    64'h4080000000000000

`define ONE40                                   40'h3FE0000000

`define EIGHT40                         40'h4040000000

`define ONE32                                   32'h7F000000

`define EIGHT32                         32'h42000000

`define FIVETWELVE32    32'h48000000

module fpSigmoid(clk, ce, a, o);

parameter WID = 128;

`include "fpSize.sv"

input clk;

input ce;

input [WID-1:0] a;

output reg [WID-1:0] o;

wire [4:0] cmp1_o;

reg [4:0] cmp2_o;

// Just the mantissa is stored in the table to economize on the storate.

// The exponent is always the same value (0x3ff). Only the top 32 bits of

// the mantissa are stored.

(* ram_style="block" *)

reg [31:0] SigmoidLUT [0:1023];

// Check if the input is in the range (-8 to +8)

// We take the absolute value by trimming off the sign bit.

generate begin : ext

if (WID==80)

fp_cmp_unit #(WID) u1 (.a(a & 80'h7FFFFFFFFFFFFFFFFFFF), .b(`EIGHT80), .o(cmp1_o), .nanx() );

else if (WID==64)

fp_cmp_unit #(WID) u1 (.a(a & 64'h7FFFFFFFFFFFFFFF), .b(`EIGHT64), .o(cmp1_o), .nanx() );

else if (WID==40)

fp_cmp_unit #(WID) u1 (.a(a & 40'h7FFFFFFFFF), .b(`EIGHT40), .o(cmp1_o), .nanx() );

else if (WID==32)

fp_cmp_unit #(WID) u1 (.a(a & 32'h7FFFFFFF), .b(`EIGHT32), .o(cmp1_o), .nanx() );

else begin

        always @*

        begin

                $display("Sigmoid: unsupported width.");

                $stop;

        end

end

end

endgenerate

initial begin

`include "D:\Cores6\nvio\v1\rtl\fpUnit\SigTbl.ver"

end

// Quickly multiply number by 64 (it is in range -8 to 8) then convert to integer to get

// table index = add 6 to exponent then convert to integer

wire sa;

wire [EMSB:0] xa;

wire [FMSB:0] ma;

fpDecomp #(WID) u1 (.i(a), .sgn(sa), .exp(xa), .man(ma), .fract(), .xz(), .vz(), .xinf(), .inf(), .nan() );

reg [9:0] lutadr;

wire [5:0] lzcnt;

wire [WID-1:0] a1;

wire [WID-1:0] i1, i2;

wire [EMSB:0] xa1 = xa + 4'd6;

assign a1 = {sa,xa1,ma};        // we know the exponent won't overflow

wire [31:0] man32a = SigmoidLUT[lutadr];

wire [31:0] man32b = lutadr==10'h3ff ? man32a : SigmoidLUT[lutadr+1];

wire [31:0] man32;

wire [79:0] sig80;

generate begin : la

if (WID >= 40) begin

wire [15:0] eps = ma[FMSB-10:FMSB-10-15];

wire [47:0] p = (man32b - man32a) * eps;

assign man32 = man32a + (p >> 26);

cntlz32 u3 (man32,lzcnt);

end

else if (WID==32) begin

wire [12:0] eps = ma[FMSB-10:0];

wire [43:0] p = (man32b - man32a) * eps;

assign man32 = man32a + (p >> 26);

cntlz32 u3 (man32,lzcnt);

end

end

endgenerate

wire [31:0] man32s = man32 << (lzcnt + 2'd1);    // +1 to hide leading one

// Convert to integer

f2i #(WID) u2

(

  .clk(clk),

  .ce(1'b1),

  .i(a1),

  .o(i2)

);

assign i1 = i2 + 512;

always @(posedge clk)

  if (ce) cmp2_o <= cmp1_o;

// We know the integer is in range 0 to 1023

always @(posedge clk)

  if(ce) lutadr <= i1[9:0];

reg sa1,sa2;

always @(posedge clk)

if (ce) sa1 <= a[WID-1];

always @(posedge clk)

if (ce) sa2 <= sa1;

generate begin : ooo

if (WID==80) begin

wire [14:0] ex1 = 15'h3ffe - lzcnt;

always @(posedge clk)

if (ce) begin

        if (cmp2_o[1])  // abs(a) less than 8 ?

          o <= {1'b0,ex1,man32s[31:0],32'd0};

        else

          o <= sa1 ? 80'h0 : `ONE80;

end

end

else if (WID==64) begin

wire [10:0] ex1 = 11'h3fe - lzcnt;

always @(posedge clk)

if (ce) begin

        if (cmp2_o[1])  // abs(a) less than 8 ?

          o <= {1'b0,ex1,man32s[31:0],20'd0};

        else

          o <= sa1 ? 64'h0 : `ONE64;

end

end

else if (WID==40) begin

wire [9:0] ex1 = 10'h1fe - lzcnt;

always @(posedge clk)

if (ce) begin

        if (cmp2_o[1])  // abs(a) less than 8 ?

          o <= {1'b0,ex1,man32s[31:3]};

        else

          o <= sa1 ? 40'h0 : `ONE40;

end

end

else if (WID==32) begin

wire [7:0] ex1 = 8'h7e - lzcnt;

always @(posedge clk)

if (ce) begin

        if (cmp2_o[1])  // abs(a) less than 8 ?

          o <= {1'b0,ex1,man32s[31:9]};

        else

          o <= sa1 ? 32'h0 : `ONE32;

end

end

end

endgenerate

endmodule