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

//        __

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

//    \  __ /    All rights reserved.

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

//       ||

//

//      intToPosit.sv

//    - integer to posit number converter

//    - 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 .

//

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

`include "positConfig.sv"

module intToPosit(i, o);

`include "positSize.sv"

localparam rs = $clog2(PSTWID-1);

localparam lzs = $clog2(PSTWID-2);

input [PSTWID-1:0] i;

output [PSTWID-1:0] o;

wire [PSTWID*2-1+es+3-2:0] tmp, tmp1;

wire [PSTWID-2:0] ii = i[PSTWID-1] ? -i : i;

wire [lzs:0] lzcnt;

wire [PSTWID-1:0] rnd_ulp, tmp2, tmp2_rnd_ulp;

integer n;

positCntlz #(.PSTWID(PSTWID)) u1 (.i(ii[PSTWID-2:0]), .o(lzcnt));

wire sgn = i[PSTWID-1];

wire [rs:0] rgm = (PSTWID - (lzcnt + 2)) >> es;

wire [PSTWID-3:0] sig = ii << lzcnt;  // left align significand, chop off leading one

generate begin : gExpandedPosit

  // The number is represented as 1.x so for an integer it

  // always needs to be left shifted.

  // Add three trailers for guard, round and sticky.

  if (es > 0) begin

    // exp = lzcnt mod (2**es)

    // remember es is constant so there are no shifts really

    wire [es-1:0] exp = (PSTWID - (lzcnt + 2)) & {es{1'b1}};

    assign tmp = {{{PSTWID-1{1'b1}},1'b0},exp,sig,3'b0};

  end

  else

    assign tmp = {{{PSTWID-1{1'b1}},1'b0},sig,3'b0};

end

endgenerate

// Compute regime shift amount = number of bits to represent regime

// Need one extra bit for the terminator, and one extra '1' bit.

wire [rs:0] rgm_sh = rgm + 2'd2;

assign tmp1 = tmp >> rgm_sh;

wire L = tmp[rgm_sh-0+es];

wire G = tmp[rgm_sh-1+es];

wire R = tmp[rgm_sh-2+es];

reg S;

wire ulp;

always @*

begin

  S = 0;

  for (n = 0; n < PSTWID; n = n + 1) begin

    if (n < rgm_sh - 2 + es)

      S = S | tmp[n];

  end

end

// Extract the bits representing the number, note leave off sign bit

assign tmp2 = tmp1[PSTWID-3+es+3:es+2];

// Round

assign ulp = ((G & (R | S)) | (L & G & ~(R | S)));

assign rnd_ulp = {{PSTWID-1{1'b0}},ulp};

assign tmp2_rnd_ulp = tmp2 + rnd_ulp;

// Final output

assign o = i=={PSTWID{1'b0}} ? {PSTWID{1'b0}} : sgn ? -tmp2_rnd_ulp : tmp2_rnd_ulp;

endmodule