Subversion Repositories ft816float

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

//        __

//   \\__/ o\    (C) 2006-2016  Robert Finch, Stratford

//    \  __ /    All rights reserved.

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

//       ||

//

// 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/>.    

//

//      fpAddsub.v

//  - floating point adder/subtracter

//  - two cycle latency

//  - can issue every clock cycle

//  - parameterized width

//  - IEEE 754 representation

//

//      This adder/subtractor handles denormalized numbers.

// It has a two cycle latency.

// 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.

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

//

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

parameter WID = 32;

localparam MSB = WID-1;

localparam EMSB = WID==80 ? 14 :

                  WID==64 ? 10 :

                                  WID==52 ? 10 :

                                  WID==48 ? 10 :

                                  WID==44 ? 10 :

                                  WID==42 ? 10 :

                                  WID==40 ?  9 :

                                  WID==32 ?  7 :

                                  WID==24 ?  6 : 4;

localparam FMSB = WID==80 ? 63 :

                  WID==64 ? 51 :

                                  WID==52 ? 39 :

                                  WID==48 ? 35 :

                                  WID==44 ? 31 :

                                  WID==42 ? 29 :

                                  WID==40 ? 28 :

                                  WID==32 ? 22 :

                                  WID==24 ? 15 : 9;

localparam WX = 3;

localparam FX = (FMSB+1)*2-1;   // the MSB of the expanded fraction

localparam EX = FX + WX + EMSB + 1;

input clk;              // system clock

input ce;               // core clock enable

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

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

input [WID-1:0] a;       // operand a

input [WID-1:0] b;       // operand b

output [EX+1:0] o;       // output

// variables

wire so;                        // sign output

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

reg [EMSB:0] xo1;        // de normalized exponent output

wire [FX+WX:0] mo;       // mantissa output

reg [FX+WX:0] mo1;       // mantissa output

// There's an extra bit output in the mantissa to allow for three whole

// digits which the normalizer uses.

assign o = {so,xo,mo};

// operands sign,exponent,mantissa

wire sa, sb;

wire [EMSB:0] xa, xb;

wire [FMSB:0] ma, mb;

wire [FMSB+1:0] fracta, fractb;

wire [FMSB+1:0] fracta1, fractb1;

// which has greater magnitude ? Used for sign calc

wire xa_gt_xb = xa > xb;

wire xa_gt_xb1;

wire a_gt_b = xa_gt_xb || (xa==xb && ma > mb);

wire a_gt_b1;

wire az, bz;    // operand a,b is zero

wire adn, bdn;          // a,b denormalized ?

wire xaInf, xbInf;

wire aInf, bInf, aInf1, bInf1;

wire aNan, bNan, aNan1, bNan1;

wire [EMSB:0] xad = xa|adn;      // operand a exponent, compensated for denormalized numbers

wire [EMSB:0] xbd = xb|bdn; // operand b exponent, compensated for denormalized numbers

fpDecompose #(WID) u1a (.i(a), .sgn(sa), .exp(xa), .man(ma), .fract(fracta), .xz(adn), .vz(az), .xinf(xaInf), .inf(aInf), .nan(aNan) );

fpDecompose #(WID) u1b (.i(b), .sgn(sb), .exp(xb), .man(mb), .fract(fractb), .xz(bdn), .vz(bz), .xinf(xbInf), .inf(bInf), .nan(bNan) );

// 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

wire realOp = op ^ sa ^ sb;

wire realOp1;

wire op1;

// Find out if the result will be zero.

wire resZero = (realOp && xa==xb && ma==mb) ||  // subtract, same magnitude

                           (az & bz);           // both a,b zero

// 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.

always @(xaInf,xbInf,resZero,xa,xb,xa_gt_xb)

        xo1 = (xaInf&xbInf) ? xa : resZero ? 0 : xa_gt_xb ? xa : xb;

// Compute output sign

reg so1;

always @*

        case ({resZero,sa,op,sb})       // synopsys full_case parallel_case

        4'b0000: so1 <= 0;                       // + + + = +

        4'b0001: so1 <= !a_gt_b;        // + + - = sign of larger

        4'b0010: so1 <= !a_gt_b;        // + - + = sign of larger

        4'b0011: so1 <= 0;                       // + - - = +

        4'b0100: so1 <= a_gt_b;         // - + + = sign of larger

        4'b0101: so1 <= 1;                      // - + - = -

        4'b0110: so1 <= 1;                      // - - + = -

        4'b0111: so1 <= a_gt_b;         // - - - = sign of larger

        4'b1000: so1 <= 0;                       //  A +  B, sign = +

        4'b1001: so1 <= rm==3;          //  A + -B, sign = + unless rounding down

        4'b1010: so1 <= rm==3;          //  A -  B, sign = + unless rounding down

        4'b1011: so1 <= 0;                       // +A - -B, sign = +

        4'b1100: so1 <= rm==3;          // -A +  B, sign = + unless rounding down

        4'b1101: so1 <= 1;                      // -A + -B, sign = -

        4'b1110: so1 <= 1;                      // -A - +B, sign = -

        4'b1111: so1 <= rm==3;          // -A - -B, sign = + unless rounding down

        endcase

delay2 #(EMSB+1) d1(.clk(clk), .ce(ce), .i(xo1), .o(xo) );

delay2 #(1)      d2(.clk(clk), .ce(ce), .i(so1), .o(so) );

// Compute the difference in exponents, provides shift amount

wire [EMSB:0] xdiff = xa_gt_xb ? xad - xbd : xbd - xad;

wire [6:0] xdif = xdiff > FMSB+3 ? FMSB+3 : xdiff;

wire [6:0] xdif1;

// determine which fraction to denormalize

wire [FMSB+1:0] mfs = xa_gt_xb ? fractb : fracta;

wire [FMSB+1:0] mfs1;

// Determine the sticky bit

wire sticky, sticky1;

redor64 u1 (.a(xdif), .b({mfs,2'b0}), .o(sticky) );

// register inputs to shifter and shift

delay1 #(1)      d16(.clk(clk), .ce(ce), .i(sticky), .o(sticky1) );

delay1 #(7)      d15(.clk(clk), .ce(ce), .i(xdif),   .o(xdif1) );

delay1 #(FMSB+2) d14(.clk(clk), .ce(ce), .i(mfs),    .o(mfs1) );

wire [FMSB+3:0] md1 = ({mfs1,2'b0} >> xdif1)|sticky1;

// sync control signals

delay1 #(1) d4 (.clk(clk), .ce(ce), .i(xa_gt_xb), .o(xa_gt_xb1) );

delay1 #(1) d17(.clk(clk), .ce(ce), .i(a_gt_b), .o(a_gt_b1) );

delay1 #(1) d5 (.clk(clk), .ce(ce), .i(realOp), .o(realOp1) );

delay1 #(FMSB+2) d5a(.clk(clk), .ce(ce), .i(fracta), .o(fracta1) );

delay1 #(FMSB+2) d6a(.clk(clk), .ce(ce), .i(fractb), .o(fractb1) );

delay1 #(1) d7 (.clk(clk), .ce(ce), .i(aInf), .o(aInf1) );

delay1 #(1) d8 (.clk(clk), .ce(ce), .i(bInf), .o(bInf1) );

delay1 #(1) d9 (.clk(clk), .ce(ce), .i(aNan), .o(aNan1) );

delay1 #(1) d10(.clk(clk), .ce(ce), .i(bNan), .o(bNan1) );

delay1 #(1) d11(.clk(clk), .ce(ce), .i(op), .o(op1) );

// Sort operands and perform add/subtract

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

wire [FMSB+3:0] oa = xa_gt_xb1 ? {fracta1,2'b0} : md1;

wire [FMSB+3:0] ob = xa_gt_xb1 ? md1 : {fractb1,2'b0};

wire [FMSB+3:0] oaa = a_gt_b1 ? oa : ob;

wire [FMSB+3:0] obb = a_gt_b1 ? ob : oa;

wire [FMSB+4:0] mab = realOp1 ? oaa - obb : oaa + obb;

always @*

        casex({aInf1&bInf1,aNan1,bNan1})

        3'b1xx:         mo1 = {1'b0,op1,{FMSB-1{1'b0}},op1,{FMSB{1'b0}}};       // inf +/- inf - generate QNaN on subtract, inf on add

        3'bx1x:         mo1 = {1'b0,fracta1[FMSB+1:0],{FMSB{1'b0}}};

        3'bxx1:         mo1 = {1'b0,fractb1[FMSB+1:0],{FMSB{1'b0}}};

        default:        mo1 = {mab,{FMSB-1{1'b0}}};     // mab has an extra lead bit

        endcase

delay1 #(FX+WX+1) d3(.clk(clk), .ce(ce), .i(mo1), .o(mo) );

endmodule

module fpAddsub_tb();

reg clk;

wire ce = 1'b1;

wire [2:0] rm = 3'b0;

wire [57:0] o1,o2,o3,o4,o5,o6;

wire [35:0] o11,o12,o13;

wire [31:0] o21,o22,o23;

initial begin

  clk = 1'b0;

end

always #10 clk = ~clk;

fpAddsub u1 (clk, ce, rm, 1'b0, 32'h0, 32'h0, o1);  // zero plus zero

fpAddsub u2 (clk, ce, rm, 1'b1, 32'h0, 32'h0, o2);  // zero minus zero

fpAddsub u3 (clk, ce, rm, 1'b0, 32'h3F000000, 32'h3F000000, o3);  // .5 + .5

fpAddsub u4 (clk, ce, rm, 1'b0, 32'h43520000, 32'h41700000, o4);  // 210+15

fpAddsub u5 (clk, ce, rm, 1'b1, 32'hC3520000, 32'hC1700000, o5);  // -210- -15

fpNormalize u11 (clk, ce, 1'b0, o3, o11);

fpNormalize u12 (clk, ce, 1'b0, o4, o12);

fpNormalize u13 (clk, ce, 1'b0, o5, o13);

fpRound u21 (3'd1, o11, o21);         // zero for zero

fpRound u22 (3'd1, o12, o22); // 

fpRound u23 (3'd1, o13, o23); // 

endmodule