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

//        __

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

//    \  __ /    All rights reserved.

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

//       ||

//

//      DFPAddsub.sv

//

// 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

//    list of conditions and the following disclaimer.

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

module DFPAddsub(clk, ce, rm, op, a, b, o);

parameter N=33;

input clk;

input ce;

input [2:0] rm;

input op;

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

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

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

parameter TRUE = 1'b1;

parameter FALSE = 1'b0;

wire sa, sb;

wire sxa, sxb;

wire adn, bdn;

wire xainf, xbinf;

wire ainf, binf;

wire aNan, bNan;

wire [15:0] xa, xb;

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

wire [15:0] xabdif4;

BCDSub4 ubcds1(

        .ci(1'b0),

        .a(xa_gt_xb4 ? xa4 : xb4),

        .b(xa_gt_xb4 ? xb4 : xa4),

        .o(xabdif4),

        .c(),

        .c8()

);

wire [(N+1)*4-1:0] oss10;

wire oss10c;

BCDAddN #(.N(N+1)) ubcdan1

(

        .ci(1'b0),

        .a(oaa10),

        .b(obb10),

        .o(oss10),

        .co(oss10c)

);

wire [(N+1)*4-1:0] odd10;

wire odd10c;

BCDSubN #(.N(N+1)) ubcdsn1

(

        .ci(1'b0),

        .a(oaa10),

        .b(obb10),

        .o(odd10),

        .co(odd10c)

);

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

// Clock #1

// - decode the input operands

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

reg op1;

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

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

always @(posedge clk)

  if (ce) op1 <= op;

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

// Clock #2

//

// Figure out which operation is really needed an add or subtract ?

// If the signs are the same, use the orignal op,

// otherwise flip the operation

//  a +  b = add,+

//  a + -b = sub, so of larger

// -a +  b = sub, so of larger

// -a + -b = add,-

//  a -  b = sub, so of larger

//  a - -b = add,+

// -a -  b = add,-

// -a - -b = sub, so of larger

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

reg realOp2;

reg op2;

reg [15:0] xa2, xb2;

reg az2, bz2;

reg xa_gt_xb2;

reg [N*4-1:0] siga2, sigb2;

reg sigeq, siga_gt_sigb;

reg xa_gt_xb2;

reg expeq;

reg sxo2;

always @(posedge clk)

  if (ce) realOp2 = op1 ^ sa ^ sb;

always @(posedge clk)

  if (ce) op2 <= op1;

always @(posedge clk)

  if (ce) xa2 <= xa;

always @(posedge clk)

  if (ce) xb2 <= xb;

always @(posedge clk)

  if (ce) siga2 <= siga;

always @(posedge clk)

  if (ce) sigb2 <= sigb;

always @(posedge clk)

  if (ce) az2 <= az;

always @(posedge clk)

  if (ce) bz2 <= bz;

always @(posedge clk)

  if (ce)

        if (sxa & ~sxb)

                xa_gt_xb2 <= TRUE;

        else if (~sxa & sxb)

                xa_gt_xb2 <= FALSE;

        else

                xa_gt_xb2 <= sxa ? xa > xb : xa < xb;

always @(posedge clk)

  if (ce)

        sxo2 <= sxa|sxb;

always @(posedge clk)

  if (ce) sigeq <= siga==sigb;

always @(posedge clk)

  if (ce) siga_gt_sigb <= siga > sigb;

always @(posedge clk)

  if (ce) expeq <= {sxa,xa}=={sxb,xb};

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

// Clock #3

//

// Find out if the result will be zero.

// Determine which fraction to denormalize

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

//

reg [15:0] xa3, xb3;

reg resZero3;

wire xaInf3, xbInf3;

reg xa_gt_xb3;

reg a_gt_b3;

reg op3;

wire sa3, sb3;

wire [2:0] rm3;

reg [N*4-1:0] mfs3;

always @(posedge clk)

  if (ce) resZero3 <= (realOp2 & expeq & sigeq) ||      // subtract, same magnitude

                           (az2 & bz2);               // both a,b zero

always @(posedge clk)

  if (ce) xa3 <= xa2;

always @(posedge clk)

  if (ce) xb3 <= xb2;

always @(posedge clk)

  if (ce) xa_gt_xb3 <= xa_gt_xb2;

always @(posedge clk)

  if (ce) a_gt_b3 <= xa_gt_xb2 | (expeq & siga_gt_sigb);

always @(posedge clk)

  if (ce) op3 <= op2;

always @(posedge clk)

  if (ce) mfs3 = xa_gt_xb2 ? sigb2 : siga2;

delay #(.WID(1), .DEP(2)) udly3c (.clk(clk), .ce(ce), .i(sa), .o(sa3));

delay #(.WID(1), .DEP(2)) udly3d (.clk(clk), .ce(ce), .i(sb), .o(sb3));

delay #(.WID(3), .DEP(3)) udly3e (.clk(clk), .ce(ce), .i(rm), .o(rm3));

delay #(.WID(1), .DEP(2)) udly3f (.clk(clk), .ce(ce), .i(aInf), .o(aInf3));

delay #(.WID(1), .DEP(2)) udly3g (.clk(clk), .ce(ce), .i(bInf), .o(bInf3));

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

// Clock #4

//

// Compute output exponent

//

// The output exponent is the larger of the two exponents,

// unless a subtract operation is in progress and the two

// numbers are equal, in which case the exponent should be

// zero.

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

reg [15:0] xa4, xb4;

reg [15:0] xo4;

reg xa_gt_xb4;

always @(posedge clk)

  if (ce) xa4 <= xa3;

always @(posedge clk)

  if (ce) xb4 <= xb3;

always @(posedge clk)

        if (ce) xo4 <= resZero3 ? 16'd0 : xa_gt_xb3 ? xa3 : xb3;

always @(posedge clk)

  if (ce) xa_gt_xb4 <= xa_gt_xb3;

// Compute output sign

reg so4;

always @*

        case ({resZero3,sa3,op3,sb3})   // synopsys full_case parallel_case

        4'b0000: so4 <= 0;                      // - + - = -

        4'b0001: so4 <= !a_gt_b3;       // - + + = sign of larger

        4'b0010: so4 <= !a_gt_b3;       // - - - = sign of larger

        4'b0011: so4 <= 0;                      // - - + = -

        4'b0100: so4 <= a_gt_b3;                // + + - = sign of larger

        4'b0101: so4 <= 1;                      // + + + = +

        4'b0110: so4 <= 1;                      // + - - = +

        4'b0111: so4 <= a_gt_b3;                // + - + = sign of larger

        4'b1000: so4 <= 0;                      //  -A +  -B, sign = -

        4'b1001: so4 <= (rm3==3'd3);            //  -A + B, sign = + unless rounding down

        4'b1010: so4 <= (rm3==3'd3);            //  -A - -B, sign = + unless rounding down

        4'b1011: so4 <= 0;                      // -A - B, sign = -

        4'b1100: so4 <= (rm3==3'd3);            // A -  B, sign = + unless rounding down

        4'b1101: so4 <= 1;                      // A + B, sign = +

        4'b1110: so4 <= 1;                      // A - -B, sign = +

        4'b1111: so4 <= (rm3==3'd3);            // -A - -B, sign = + unless rounding down

        endcase

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

// Clock #5

//

// Compute the difference in exponents, provides shift amount

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

reg [15:0] xdiff5;

always @(posedge clk)

  if (ce) xdiff5 <= xabdif4;

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

// Clock #6

//

// Compute the difference in exponents, provides shift amount

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

// If the difference in the exponent is 24 or greater (assuming 24 nybble dfp or

// less) then all of the bits will be shifted out to zero. There is no need to

// keep track of a difference more than 24.

reg [11:0] xdif6;

wire [N*4-1:0] mfs6;

always @(posedge clk)

  if (ce) xdif6 <= xdiff5 > N ? N : xdiff5[7:0];

delay #(.WID(N*4), .DEP(3)) udly6a (.clk(clk), .ce(ce), .i(mfs3), .o(mfs6));

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

// Clock #7

//

// Determine the sticky bit. The sticky bit is the bitwise or of all the bits

// being shifted out the right side. The sticky bit is computed here to

// reduce the number of regs required.

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

reg sticky6;

wire sticky7;

wire [7:0] xdif7;

wire [N*4-1:0] mfs7;

wire [7:0] xdif6a = {xdif6[7:4] * 10 + xdif6[3:0],2'b00};       // Convert base then *4

integer n;

always @* begin

        sticky6 = 1'b0;

        for (n = 0; n < N*4; n = n + 4)

                if (n <= xdif6a)

                        sticky6 = sticky6| mfs6[n]|mfs6[n+1]|mfs6[n+2]|mfs6[n+3];       // non-zeero nybble

end

// register inputs to shifter and shift

delay1 #(1)  d16(.clk(clk), .ce(ce), .i(sticky6), .o(sticky7) );

delay1 #(8)  d15(.clk(clk), .ce(ce), .i(xdif6a),   .o(xdif7) );

delay1 #(N*4) d14(.clk(clk), .ce(ce), .i(mfs6),    .o(mfs7) );

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

// Clock #8

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

reg [(N+1)*4-1:0] md8;

wire [N*4-1:0] siga8, sigb8;

wire xa_gt_xb8;

wire a_gt_b8;

always @(posedge clk)

  if (ce) md8 <= ({mfs7,4'b0} >> xdif7)|sticky7; // xdif7 is a multiple of four

// sync control signals

delay #(.WID(1), .DEP(4)) udly8a (.clk(clk), .ce(ce), .i(xa_gt_xb4), .o(xa_gt_xb8));

delay #(.WID(1), .DEP(5)) udly8b (.clk(clk), .ce(ce), .i(a_gt_b3), .o(a_gt_b8));

delay #(.WID(N*4), .DEP(6)) udly8d (.clk(clk), .ce(ce), .i(siga2), .o(siga8));

delay #(.WID(N*4), .DEP(6)) udly8e (.clk(clk), .ce(ce), .i(sigb2), .o(sigb8));

delay #(.WID(1), .DEP(5)) udly8j (.clk(clk), .ce(ce), .i(op3), .o(op8));

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

// Clock #9

// Sort operands and perform add/subtract

// addition can generate an extra bit, subtract can't go negative

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

reg [(N+1)*4-1:0] oa9, ob9;

reg a_gt_b9;

always @(posedge clk)

  if (ce) oa9 <= xa_gt_xb8 ? {siga8,4'b0} : md8;

always @(posedge clk)

  if (ce) ob9 <= xa_gt_xb8 ? md8 : {sigb8,4'b0};

always @(posedge clk)

  if (ce) a_gt_b9 <= a_gt_b8;

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

// Clock #10

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

reg [(N+1)*4-1:0] oaa10;

reg [(N+1)*4-1:0] obb10;

wire realOp10;

reg [15:0] xo10;

always @(posedge clk)

  if (ce) oaa10 <= a_gt_b9 ? oa9 : ob9;

always @(posedge clk)

  if (ce) obb10 <= a_gt_b9 ? ob9 : oa9;

delay #(.WID(1), .DEP(8)) udly10a (.clk(clk), .ce(ce), .i(realOp2), .o(realOp10));

delay #(.WID(16), .DEP(6)) udly10b (.clk(clk), .ce(ce), .i(xo4), .o(xo10));

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

// Clock #11

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

reg [(N+1)*4-1:0] mab11;

reg mab11c;

wire [N*4-1:0] siga11, sigb11;

wire abInf11;

wire aNan11, bNan11;

reg xoinf11;

wire op11;

always @(posedge clk)

  if (ce) mab11 <= realOp10 ? odd10 : oss10;

always @(posedge clk)

        if (ce) mab11c <= realOp10 ? odd10c : oss10c;

delay #(.WID(1), .DEP(8)) udly11a (.clk(clk), .ce(ce), .i(aInf3&bInf3), .o(abInf11));

delay #(.WID(1), .DEP(10)) udly11c (.clk(clk), .ce(ce), .i(aNan), .o(aNan11));

delay #(.WID(1), .DEP(10)) udly11d (.clk(clk), .ce(ce), .i(bNan), .o(bNan11));

delay #(.WID(1), .DEP(3)) udly11e (.clk(clk), .ce(ce), .i(op8), .o(op11));

delay #(.WID(N*4), .DEP(3)) udly11f (.clk(clk), .ce(ce), .i(siga8), .o(siga11));

delay #(.WID(N*4), .DEP(3)) udly11g (.clk(clk), .ce(ce), .i(sigb8), .o(sigb11));

always @(posedge clk)

  if (ce) xoinf11 <= xo10==16'h9999;

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

// Clock #12

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

reg [(N+1)*4*2-1:0] mo12;       // mantissa output

reg [3:0] st12;

wire sxo11;

wire so11;

delay #(.WID(1), .DEP(9)) udly12a (.clk(clk), .ce(ce), .i(sxo2), .o(sxo11));

delay #(.WID(1), .DEP(7)) udly12b (.clk(clk), .ce(ce), .i(so4), .o(so11));

always @(posedge clk)

if (ce) begin

        st12[0] <= sxo11;

        st12[1] <= abInf11;

        st12[2] <= so11;

        st12[3] <= aNan11|bNan11;

end

always @(posedge clk)

if (ce)

        casez({abInf11,aNan11,bNan11,xoinf11})

        4'b1???:        // inf +/- inf - generate QNaN on subtract, inf on add

                if (op11)

                        mo12 <= {4'h9,{(N+1)*4*2-4{1'd0}}};

                else

                        mo12 <= {(N+1)*2{4'h9}};

        4'b01??:        mo12 <= {4'b0,siga11[107:0],{(N+1)*4{1'd0}}};

        4'b001?:        mo12 <= {4'b0,sigb11[107:0],{(N+1)*4{1'd0}}};

        4'b0001:        mo12 <= {(N+1)*4*2{1'd0}};

        default:        mo12 <= {3'b0,mab11c,mab11,{N*4{1'd0}}};        // mab has an extra lead bit and four trailing bits

        endcase

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

// Clock #13

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

wire so;                        // sign output

wire [3:0] st;

wire [15:0] xo; // de normalized exponent output

wire [(N+1)*4*2-1:0] mo;        // mantissa output

delay #(.WID(4), .DEP(1)) u13c (.clk(clk), .ce(ce), .i(st12), .o(st[3:0]) );

delay #(.WID(1), .DEP(9)) udly13a (.clk(clk), .ce(ce), .i(so4), .o(so));

delay #(.WID(16), .DEP(3)) udly13b (.clk(clk), .ce(ce), .i(xo10), .o(xo));

delay #(.WID((N+1)*4*2), .DEP(1)) u13d (.clk(clk), .ce(ce), .i(mo12), .o(mo) );

assign o = {st,xo,mo};

endmodule

module DFPAddsubnr(clk, ce, rm, op, a, b, o);

parameter N=33;

input clk;              // system clock

input ce;               // core clock enable

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

input op;               // operation 0 = add, 1 = subtract

input [N*4+16+4-1:0] a; // operand a

input [N*4+16+4-1:0] b; // operand b

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

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

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

DFPAddsub    u1 (clk, ce, rm, op, a, b, o1);

DFPNormalize u2(.clk(clk), .ce(ce), .under_i(1'b0), .i(o1), .o(fpn0) );

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

endmodule