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

//        __

//   \\__/ o\    (C) 2006-2020  Robert Finch, Waterloo

//    \  __ /    All rights reserved.

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

//       ||

//

//      DFPDivide.sv

//    - decimal floating point divider

//    - parameterized width

//

//

// BSD 3-Clause License

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// modification, are permitted provided that the following conditions are met:

//

// 1. Redistributions of source code must retain the above copyright notice, this

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//

//      Floating Point Divider

//

//Properties:

//+-inf * +-inf = -+inf    (this is handled by exOver)

//+-inf * 0     = QNaN

//+-0 / +-0      = QNaN

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

import fp::*;

module DFPDivide(rst, clk, ce, ld, op, a, b, o, done, sign_exe, overflow, underflow);

parameter N=33;

// FADD is a constant that makes the divider width a multiple of four and includes eight extra bits.

input rst;

input clk;

input ce;

input ld;

input op;

input  [N*4+16+4-1:0] a, b;

output [(N+1)*4*2+16+4-1:0] o;

output reg done;

output sign_exe;

output overflow;

output underflow;

// registered outputs

reg sign_exe=0;

reg inf=0;

reg     overflow=0;

reg     underflow=0;

reg so, sxo;

reg [3:0] st;

reg [15:0] xo;

reg [(N+1)*4*2-1:0] mo;

assign o = {st,xo,mo};

// constants

wire [15:0] infXp = 16'h9999;   // infinite / NaN - all ones

// The following is the value for an exponent of zero, with the offset

// eg. 8'h7f for eight bit exponent, 11'h7ff for eleven bit exponent, etc.

// The following is a template for a quiet nan. (MSB=1)

wire [N*4-1:0] qNaN  = {4'h1,{(N-1)*4{1'b0}}};

// variables

wire [(N+2)*4*2-1:0] divo;

// Operands

wire sa, sb;                    // sign bit

wire sxa, sxb;

wire [15:0] xa, xb;     // exponent bits

wire [N*4-1:0] siga, sigb;

wire a_dn, b_dn;                        // a/b is denormalized

wire az, bz;

wire aInf, bInf;

wire aNan,bNan;

wire done1;

wire signed [7:0] lzcnt;

// -----------------------------------------------------------

// Clock #1

// - decode the input operands

// - derive basic information

// - calculate fraction

// -----------------------------------------------------------

reg ld1;

DFPDecomposeReg u1a (.clk(clk), .ce(ce), .i(a), .sgn(sa), .sx(sxa), .exp(xa), .sig(siga), .xz(a_dn), .vz(az), .inf(aInf), .nan(aNan) );

DFPDecomposeReg u1b (.clk(clk), .ce(ce), .i(b), .sgn(sb), .sx(sxb), .exp(xb), .sig(sigb), .xz(b_dn), .vz(bz), .inf(bInf), .nan(bNan) );

delay #(.WID(1), .DEP(1)) udly1 (.clk(clk), .ce(ce), .i(ld), .o(ld1));

// -----------------------------------------------------------

// Clock #2 to N

// - calculate fraction

// -----------------------------------------------------------

wire done3a,done3;

// Perform divide

dfdiv #(N+2) u2 (.clk(clk), .ld(ld1), .a({siga,8'b0}), .b({sigb,8'b0}), .q(divo), .r(), .done(done1), .lzcnt(lzcnt));

wire [7:0] lzcnt_bin = lzcnt[3:0] + (lzcnt[7:4] * 10);

wire [(N+2)*4*2-1:0] divo1 = divo[(N+2)*4*2-1:0] << ({lzcnt_bin,2'b0}+(N*4));//WAS FPWID=128?+44

delay #(.WID(1), .DEP(3)) u3 (.clk(clk), .ce(ce), .i(done1), .o(done3a));

assign done3 = done1&done3a;

// -----------------------------------------------------------

// Clock #N+1

// - calculate exponent

// - calculate fraction

// - determine when a NaN is output

// -----------------------------------------------------------

// Compute the exponent.

// - correct the exponent for denormalized operands

// - adjust the difference by the bias (add 127)

// - also factor in the different decimal position for division

reg [15:0] ex2, ex1, ex2a, ex2b;        // sum of exponents

reg qNaNOut;

reg under1, under;

reg over1, over;

wire [15:0] xapxb, xamxb, xbmxa;

wire xapxbc, xamxbc, xbmxac;

reg sxo0;

BCDAddN #(.N(4)) u5 (.ci(1'b0), .a(xa), .b(xb), .o(xapxb), .co(xapxbc) );

BCDSubN #(.N(4)) u6 (.ci(1'b0), .a(xa), .b(xb), .o(xamxb), .co(xamxbc) );

BCDSubN #(.N(4)) u7 (.ci(1'b0), .a(xb), .b(xa), .o(xbmxa), .co(xbmxac) );

BCDSubN #(.N(5)) u10 (.ci(1'b0), .a(20'h10000), .b(ex2a), .o(ex2b), .co() );

always @*

case ({sxa,sxb})

2'b11:  begin ex2a <= xbmxa; sxo0 <= ~xbmxac; over1 <= 1'b0; under1 <= 1'b0; end

2'b10:  begin ex2a <= xapxb; sxo0 <= 1'b1; over1 <= xapxbc; under1 <= 1'b0; end

2'b01:  begin ex2a <= xapxb; sxo0 <= 1'b0; over1 <= 1'b0; under1 <= xapxbc; end

2'b00:  begin ex2a <= xamxb; sxo0 <= ~xamxbc; over1 <= 1'b0; under1 <= 1'b0; end

endcase

always @*

if (~sxo0 && ~(sa^sb))

        ex2 <= ex2b;

else

        ex2 <= ex2a;

wire [15:0] ex1a, ex1b, ex1d;

reg [15:0] ex1c;

wire sxoa, sxob, sxoc;

BCDAddN #(.N(4)) u8 (.ci(1'b0), .a(ex2), .b({8'h00,lzcnt}), .o(ex1a), .co(sxoa) );

BCDSubN #(.N(4)) u9 (.ci(1'b0), .a(ex2), .b({8'h00,lzcnt}), .o(ex1b), .co(sxob) );

BCDSubN #(.N(5)) u11 (.ci(1'b0), .a(20'h10000), .b(ex1c), .o(ex1d), .co() );

always @(posedge clk)

case(sxo0)

2'd1:   begin ex1c <= ex1b; sxo <= ~sxob; over <= over1; under <= under1; end

2'd0:   begin ex1c <= ex1a; sxo <= 1'b0; over <= over1;  under <= under1|sxob; end

endcase

always @*

if (sxo0 & sxob)        // There was a borrow on a subtract, making the number negative

        ex1 <= ex1d;

else

        ex1 <= ex1c;

always @(posedge clk)

  if (ce) qNaNOut <= (az&bz)|(aInf&bInf);

// -----------------------------------------------------------

// Clock #N+3

// -----------------------------------------------------------

always @(posedge clk)

// Simulation likes to see these values reset to zero on reset. Otherwise the

// values propagate in sim as X's.

if (rst) begin

        xo <= 1'd0;

        mo <= 1'd0;

        so <= 1'd0;

        sign_exe <= 1'd0;

        overflow <= 1'd0;

        underflow <= 1'd0;

        done <= 1'b1;

end

else if (ce) begin

  done <= 1'b0;

        if (done3&done1) begin

          done <= 1'b1;

                casez({qNaNOut|aNan|bNan,bInf,bz,over,under})

                5'b1????:               xo <= infXp;    // NaN exponent value

                5'b01???:               xo <= 1'd0;             // divide by inf

                5'b001??:               xo <= infXp;    // divide by zero

                5'b0001?:               xo <= infXp;    // overflow

                5'b00001:               xo <= 1'd0;             // underflow

                default:                xo <= ex1;      // normal or underflow: passthru neg. exp. for normalization

                endcase

                casez({aNan,bNan,qNaNOut,bInf,bz,over,aInf&bInf,az&bz})

                8'b1???????:  begin mo <= {4'h1,a[N*4-1:0],{(N+1)*4-1{1'b0}}}; st[3] <= 1'b1; end

                8'b01??????:  begin mo <= {4'h1,b[N*4-1:0],{(N+1)*4-1{1'b0}}}; st[3] <= 1'b1; end

                8'b001?????:    begin mo <= {4'h1,qNaN[N*4-1:0]|{aInf,1'b0}|{az,bz},{(N+1)*4-1{1'b0}}}; st[3] <= 1'b1; end

                8'b0001????:    begin mo <= {(N+1)*4*2-1{1'd0}};        st[3] <= 1'b0; end      // div by inf

                8'b00001???:    begin mo <= {(N+1)*4*2-1{1'd0}};        st[3] <= 1'b0; end      // div by zero

                8'b000001??:    begin mo <= {(N+1)*4*2-1{1'd0}};        st[3] <= 1'b0; end      // Inf exponent

                8'b0000001?:    begin mo <= {4'h1,qNaN|`QINFDIV,{(N+1)*4-1{1'b0}}};     st[3] <= 1'b1; end      // infinity / infinity

                8'b00000001:    begin mo <= {4'h1,qNaN|`QZEROZERO,{(N+1)*4-1{1'b0}}};   st[3] <= 1'b1; end      // zero / zero

                default:                begin mo <= divo1[(N+2)*4*2-1:8];       st[3] <= 1'b0; end      // plain div

                endcase

                st[0] <= sxo;

                st[1] <= aInf;

                st[2] <= ~(sa ^ sb);

                so              <= ~(sa ^ sb);

                sign_exe        <= sa & sb;

                overflow        <= over;

                underflow       <= under;

        end

end

endmodule

module DFPDividenr(rst, clk, ce, ld, op, a, b, o, rm, done, sign_exe, inf, overflow, underflow);

parameter N=33;

input rst;

input clk;

input ce;

input ld;

input op;

input  [N*4+16+4-1:0] a, b;

output [N*4+16+4-1:0] o;

input [2:0] rm;

output sign_exe;

output done;

output inf;

output overflow;

output underflow;

wire [(N+1)*4*2+16+4-1:0] o1;

wire sign_exe1, inf1, overflow1, underflow1;

wire [N*4+16+4-1+4:0] fpn0;

wire done1, done1a;

DFPDivide    #(.N(N)) u1 (rst, clk, ce, ld, op, a, b, o1, done1, sign_exe1, overflow1, underflow1);

DFPNormalize #(.N(N)) u2(.clk(clk), .ce(ce), .under_i(underflow1), .i(o1), .o(fpn0) );

DFPRound     #(.N(N)) u3(.clk(clk), .ce(ce), .rm(rm), .i(fpn0), .o(o) );

delay2      #(1)   u4(.clk(clk), .ce(ce), .i(sign_exe1), .o(sign_exe));

delay2      #(1)   u5(.clk(clk), .ce(ce), .i(inf1), .o(inf));

delay2      #(1)   u6(.clk(clk), .ce(ce), .i(overflow1), .o(overflow));

delay2      #(1)   u7(.clk(clk), .ce(ce), .i(underflow1), .o(underflow));

delay   #(.WID(1),.DEP(11))   u8(.clk(clk), .ce(ce), .i(done1), .o(done1a));

assign done = done1&done1a;

endmodule