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

//        __

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

//    \  __ /    All rights reserved.

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

//       ||

//

//      DFPMultiply.v

//              - decimal floating point multiplier

//              - can issue every clock cycle

//              - 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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//    this list of conditions and the following disclaimer in the documentation

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//

//

//      Floating Point Multiplier

//

//      This multiplier handles denormalized numbers.

//      The output format is of an internal expanded representation

//      in preparation to be fed into a normalization unit, then

//      rounding. Basically, it's the same as the regular format

//      except the mantissa is doubled in size, the leading two

//      bits of which are assumed to be whole bits.

//

//

//      Floating Point Multiplier

//

//      Properties:

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

//      +-inf * 0     = QNaN

//

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

import fp::*;

module DFPMultiply(clk, ce, a, b, o, sign_exe, inf, overflow, underflow);

input clk;

input ce;

input  [127:0] a, b;

output [243:0] o;

output sign_exe;

output inf;

output overflow;

output underflow;

parameter DELAY =

  (FPWID == 128 ? 17 :

  FPWID == 80 ? 17 :

  FPWID == 64 ? 13 :

  FPWID == 40 ? 8 :

  FPWID == 32 ? 2 :

  FPWID == 16 ? 2 : 2);

reg [15:0] xo1;         // extra bit for sign

reg [215:0] mo1;

// 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 [107:0] qNaN  = {4'h1,{104{1'b0}}};

// variables

reg [215:0] sig1;

wire [15:0] ex2;

// Decompose the operands

wire sa, sb;                    // sign bit

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

wire sxa, sxb;

wire [107:0] siga, sigb;

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

wire aNan, bNan, aNan1, bNan1;

wire az, bz;

wire aInf, bInf, aInf1, bInf1;

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

// Clock #1

// - decode the input operands

// - derive basic information

// - calculate exponent

// - calculate fraction

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

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

// First clock

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

reg under, over;

reg [15:0] sum_ex;

reg sx0;

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

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

// Compute the sum of the exponents.

// Exponents are sign-magnitude.

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

wire xapxbc, xamxbc, xbmxac;

BCDAddN #(.N(4)) u1c (.ci(1'b0), .a(xa), .b(xb), .o(xapxb), .co(xapxbc));

BCDSubN #(.N(4)) u1d (.ci(1'b0), .a(xa), .b(xb), .o(xamxb), .co(xamxbc));

BCDSubN #(.N(4)) u1e (.ci(1'b0), .a(xb), .b(xa), .o(xbmxa), .co(xbmxac));

always @*

        case({sxa,sxb})

        2'b11:  begin sum_ex <= xapxb; over <= xapxbc; under <= 1'b0; sx0 <= sxa; end

        2'b01:  begin sum_ex <= xbmxa; over <= 1'b0; under <= 1'b0; sx0 <= ~xbmxac; end

        2'b10:  begin sum_ex <= xamxb; over <= 1'b0; under <= 1'b0; sx0 <= ~xamxbc; end

        2'b00:  begin sum_ex <= xapxb; over <= 1'b0; under <= xapxbc; sx0 <= sxa; end

        endcase

wire [255:0] sigoo;

BCDMul32 u1f (.a({20'h0,siga}),.b({20'h0,sigb}),.o(sigoo));

always @(posedge clk)

  if (ce) sig1 <= sigoo[215:0];

// Status

wire under1, over1;

delay #(.WID(16),.DEP(DELAY)) u3 (.clk(clk), .ce(ce), .i(sum_ex), .o(ex2) );

delay #(.WID(1),.DEP(DELAY)) u2a (.clk(clk), .ce(ce), .i(aInf), .o(aInf1) );

delay #(.WID(1),.DEP(DELAY)) u2b (.clk(clk), .ce(ce), .i(bInf), .o(bInf1) );

delay #(.WID(1),.DEP(DELAY)) u6  (.clk(clk), .ce(ce), .i(under), .o(under1) );

delay #(.WID(1),.DEP(DELAY)) u7  (.clk(clk), .ce(ce), .i(over), .o(over1) );

// determine when a NaN is output

wire qNaNOut;

wire [127:0] a1,b1;

delay #(.WID(1),.DEP(DELAY)) u5 (.clk(clk), .ce(ce), .i((aInf&bz)|(bInf&az)), .o(qNaNOut) );

delay #(.WID(1),.DEP(DELAY)) u14 (.clk(clk), .ce(ce), .i(aNan), .o(aNan1) );

delay #(.WID(1),.DEP(DELAY)) u15 (.clk(clk), .ce(ce), .i(bNan), .o(bNan1) );

delay #(.WID(128),.DEP(DELAY))  u16 (.clk(clk), .ce(ce), .i(a), .o(a1) );

delay #(.WID(128),.DEP(DELAY))  u17 (.clk(clk), .ce(ce), .i(b), .o(b1) );

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

// Second clock

// - correct xponent and mantissa for exceptional conditions

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

wire so1, sx1;

reg [3:0] st;

delay #(.WID(1),.DEP(1)) u8 (.clk(clk), .ce(ce), .i(~(sa ^ sb)), .o(so1) );// two clock delay!

delay #(.WID(1),.DEP(1)) u9 (.clk(clk), .ce(ce), .i(sx0), .o(sx1) );// two clock delay!

always @(posedge clk)

        if (ce)

                casez({qNaNOut|aNan1|bNan1,aInf1,bInf1,over1,under1})

                5'b1????:       xo1 = infXp;    // qNaN - infinity * zero

                5'b01???:       xo1 = infXp;    // 'a' infinite

                5'b001??:       xo1 = infXp;    // 'b' infinite

                5'b0001?:       xo1 = infXp;    // result overflow

                5'b00001:       xo1 = ex2[15:0];//0;            // underflow

                default:        xo1 = ex2[15:0];        // situation normal

                endcase

// Force mantissa to zero when underflow or zero exponent when not supporting denormals.

always @(posedge clk)

        if (ce)

                casez({aNan1,bNan1,qNaNOut,aInf1,bInf1,over1|under1})

                6'b1?????:  mo1 = {4'h1,a1[103:0],108'b0};

    6'b01????:  mo1 = {4'h1,b1[103:0],108'b0};

                6'b001???:      mo1 = {4'h1,qNaN|3'd4,108'b0};  // multiply inf * zero

                6'b0001??:      mo1 = 0;        // mul inf's

                6'b00001?:      mo1 = 0;        // mul inf's

                6'b000001:      mo1 = 0;        // mul overflow

                default:        mo1 = sig1;

                endcase

always @(posedge clk)

        if (ce) begin

                st[3] <= aNan1|bNan1;

                st[2] <= so1;

                st[1] <= aInf|bInf|over;

                st[0] <= sx1;

        end

delay #(.WID(1),.DEP(DELAY+1)) u10 (.clk(clk), .ce(ce), .i(sa & sb), .o(sign_exe) );

delay1 u11 (.clk(clk), .ce(ce), .i(over1),  .o(overflow) );

delay1 u12 (.clk(clk), .ce(ce), .i(over1),  .o(inf) );

delay1 u13 (.clk(clk), .ce(ce), .i(under1), .o(underflow) );

assign o = {st,xo1,mo1,8'h00};

endmodule

// Multiplier with normalization and rounding.

module DFPMultiplynr(clk, ce, a, b, o, rm, sign_exe, inf, overflow, underflow);

input clk;

input ce;

input  [127:0] a, b;

output [127:0] o;

input [2:0] rm;

output sign_exe;

output inf;

output overflow;

output underflow;

wire [243:0] o1;

wire sign_exe1, inf1, overflow1, underflow1;

wire [131:0] fpn0;

DFPMultiply  u1 (clk, ce, a, b, o1, sign_exe1, inf1, overflow1, underflow1);

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

DFPRound     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));

endmodule