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very basic early termination passes testfloat 64-bit tests

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Katherine Parry 2022-06-28 00:16:22 +00:00
parent f25bb4a384
commit f2d05911ca
3 changed files with 29 additions and 17 deletions
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25
pipelined/src/fpu/divshiftcalc.sv
View File

@ -7,16 +7,15 @@ module divshiftcalc(
input logic [$clog2(`DIVLEN/2+3)-1:0] EarlyTermShiftDiv2M,
output logic [$clog2(`NORMSHIFTSZ)-1:0] DivShiftAmt,
output logic [`NORMSHIFTSZ-1:0] DivShiftIn,
output logic [`NE+1:0] CorrDivExp
output logic DivResDenorm,
output logic [`NE+1:0] DivDenormShift
);
logic ResDenorm;
logic [`NE+1:0] DenormShift;
logic [`NE+1:0] NormShift;
logic [`NE+1:0] Nf, NfPlus1;
// is the result denromalized
// if the exponent is 1 then the result needs to be normalized then the result is denormalizes
assign ResDenorm = DivCalcExpM[`NE+1]|(~|DivCalcExpM[`NE+1:1]&~(DivCalcExpM[0]&Quot[`DIVLEN+2]));
assign DivResDenorm = DivCalcExpM[`NE+1]|(~|DivCalcExpM[`NE+1:0]);
// select the proper fraction lengnth
if (`FPSIZES == 1) begin
assign Nf = (`NE+2)'(`NF);
@ -70,24 +69,22 @@ module divshiftcalc(
// if the result is denormalized
// 00000000x.xxxxxx... Exp = DivCalcExp
// .00000000xxxxxxx... >> NF+1 Exp = DivCalcExp+NF+1
// .000xxxxxxxxxxxx... << DivCalcExp+NF+1 Exp = 0
// .00xxxxxxxxxxxxx... << DivCalcExp+NF+1 Exp = +1
// .0000xxxxxxxxxxx... >> 1 Exp = 1
// Left shift amount = DivCalcExp+NF+1-1
assign DenormShift = Nf+DivCalcExpM;
assign DivDenormShift = Nf+DivCalcExpM;
// if the result is normalized
// 00000000x.xxxxxx... Exp = DivCalcExp
// .00000000xxxxxxx... >> NF+1 Exp = DivCalcExp+NF+1
// 00000000x.xxxxxx... << NF+1 Exp = DivCalcExp
// 00000000xx.xxxxx... << 1? Exp = DivCalcExp-1
// Left shift amount = NF+1 plus 1 if normalization required
assign NormShift = NfPlus1 + {(`NE+1)'(0), ~Quot[`DIVLEN+2]};
// 00000000.xxxxxxx... << NF Exp = DivCalcExp+1
// 00000000x.xxxxxx... << NF Exp = DivCalcExp (extra shift done afterwards)
// 00000000xx.xxxxx... << 1? Exp = DivCalcExp-1 (determined after)
// inital Left shift amount = NF
assign NormShift = Nf;
// if the shift amount is negitive then dont shift (keep sticky bit)
assign DivShiftAmt = (ResDenorm ? DenormShift[$clog2(`NORMSHIFTSZ)-1:0]&{$clog2(`NORMSHIFTSZ){~DenormShift[`NE+1]}} : NormShift[$clog2(`NORMSHIFTSZ)-1:0])+{{$clog2(`NORMSHIFTSZ)-$clog2(`DIVLEN/2+3)-1{1'b0}}, EarlyTermShiftDiv2M, 1'b0};
assign DivShiftAmt = (DivResDenorm ? DivDenormShift[$clog2(`NORMSHIFTSZ)-1:0]&{$clog2(`NORMSHIFTSZ){~DivDenormShift[`NE+1]}} : NormShift[$clog2(`NORMSHIFTSZ)-1:0])+{{$clog2(`NORMSHIFTSZ)-$clog2(`DIVLEN/2+3)-1{1'b0}}, EarlyTermShiftDiv2M&{$clog2(`DIVLEN/2+3){~DivDenormShift[`NE+1]}}, 1'b0};
// *** may be able to reduce shifter size
assign DivShiftIn = {{`NF{1'b0}}, Quot[`DIVLEN+2:0], {`NORMSHIFTSZ-`DIVLEN-3-`NF{1'b0}}};
// the quotent is in the range [.5,2) if there is no early termination
// if the quotent < 1 and not denormal then subtract 1 to account for the normalization shift
assign CorrDivExp = (ResDenorm&~DenormShift[`NE+1]) ? (`NE+2)'(0) : DivCalcExpM - {(`NE+1)'(0), ~Quot[`DIVLEN+2]};
endmodule

14
pipelined/src/fpu/lzacorrection.sv
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@ -3,14 +3,20 @@
module lzacorrection(
input logic [`NORMSHIFTSZ-1:0] Shifted, // the shifted sum before LZA correction
input logic FmaOp,
input logic DivOp,
input logic DivResDenorm,
input logic [`NE+1:0] DivCalcExpM,
input logic [`NE+1:0] DivDenormShift,
input logic [`NE+1:0] ConvNormSumExp, // exponent of the normalized sum not taking into account denormal or zero results
input logic PreResultDenorm, // is the result denormalized - calculated before LZA corection
input logic KillProdM, // is the product set to zero
input logic SumZero,
output logic [`CORRSHIFTSZ-1:0] CorrShifted, // the shifted sum before LZA correction
output logic [`NE+1:0] CorrDivExp,
output logic [`NE+1:0] SumExp // exponent of the normalized sum
);
logic [3*`NF+5:0] CorrSumShifted; // the shifted sum after LZA correction
logic [`CORRSHIFTSZ:0] CorrQuotShifted;
logic ResDenorm; // is the result denormalized
logic LZAPlus1, LZAPlus2; // add one or two to the sum's exponent due to LZA correction
@ -19,11 +25,17 @@ module lzacorrection(
assign LZAPlus2 = Shifted[`NORMSHIFTSZ-1];
// the only possible mantissa for a plus two is all zeroes - a one has to propigate all the way through a sum. so we can leave the bottom statement alone
assign CorrSumShifted = LZAPlus1 ? Shifted[`NORMSHIFTSZ-3:1] : Shifted[`NORMSHIFTSZ-4:0];
assign CorrShifted = FmaOp ? {CorrSumShifted, {`CORRSHIFTSZ-(3*`NF+6){1'b0}}} : Shifted[`NORMSHIFTSZ-1:`NORMSHIFTSZ-`CORRSHIFTSZ];
// if the msb is 1 or the exponent was one, but the shifted quotent was < 1 (Denorm)
assign CorrQuotShifted = {LZAPlus2|(DivCalcExpM==1&~LZAPlus2) ? Shifted[`NORMSHIFTSZ-1:`NORMSHIFTSZ-`CORRSHIFTSZ] : {Shifted[`NORMSHIFTSZ-2:`NORMSHIFTSZ-`CORRSHIFTSZ], 1'b0}, 1'b0};
// if the result of the divider was calculated to be denormalized, then the result was correctly normalized, so select the top shifted bits
assign CorrShifted = FmaOp ? {CorrSumShifted, {`CORRSHIFTSZ-(3*`NF+6){1'b0}}} : DivOp&~DivResDenorm ? CorrQuotShifted[`CORRSHIFTSZ-1:0] : Shifted[`NORMSHIFTSZ-1:`NORMSHIFTSZ-`CORRSHIFTSZ];
// Determine sum's exponent
// if plus1 If plus2 if said denorm but norm plus 1 if said denorm but norm plus 2
assign SumExp = (ConvNormSumExp+{{`NE+1{1'b0}}, LZAPlus1&~KillProdM}+{{`NE{1'b0}}, LZAPlus2&~KillProdM, 1'b0}+{{`NE+1{1'b0}}, ~ResDenorm&PreResultDenorm&~KillProdM}+{{`NE+1{1'b0}}, &ConvNormSumExp&Shifted[3*`NF+6]&~KillProdM}) & {`NE+2{~(SumZero|ResDenorm)}};
// recalculate if the result is denormalized
assign ResDenorm = PreResultDenorm&~Shifted[`NORMSHIFTSZ-3]&~Shifted[`NORMSHIFTSZ-2];
// the quotent is in the range [.5,2) if there is no early termination
// if the quotent < 1 and not denormal then subtract 1 to account for the normalization shift
assign CorrDivExp = ((DivResDenorm)&~DivDenormShift[`NE+1]) ? (`NE+2)'(0) : DivCalcExpM - {(`NE+1)'(0), ~LZAPlus2};
endmodule

7
pipelined/src/fpu/postprocess.sv
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@ -112,6 +112,8 @@ module postprocess(
logic UfLSBRes;
logic Sqrt;
logic [`FMTBITS-1:0] OutFmt;
logic DivResDenorm;
logic [`NE+1:0] DivDenormShift;
// signals to help readability
assign Signed = FOpCtrlM[0];
@ -144,7 +146,7 @@ module postprocess(
.XZeroM, .IntToFp, .OutFmt, .CvtResUf, .CvtShiftIn);
fmashiftcalc fmashiftcalc(.SumM, .ZExpM, .ProdExpM, .FmaNormCntM, .FmtM, .KillProdM, .ConvNormSumExp,
.ZDenormM, .SumZero, .PreResultDenorm, .FmaShiftAmt, .FmaShiftIn);
divshiftcalc divshiftcalc(.FmtM, .Quot, .DivCalcExpM, .EarlyTermShiftDiv2M, .CorrDivExp, .DivShiftAmt, .DivShiftIn);
divshiftcalc divshiftcalc(.FmtM, .Quot, .DivCalcExpM, .EarlyTermShiftDiv2M, .DivResDenorm, .DivDenormShift, .DivShiftAmt, .DivShiftIn);
always_comb
case(PostProcSelM)
@ -169,7 +171,8 @@ module postprocess(
normshift normshift (.ShiftIn, .ShiftAmt, .Shifted);
lzacorrection lzacorrection(.FmaOp, .KillProdM, .PreResultDenorm, .ConvNormSumExp,
.SumZero, .Shifted, .SumExp, .CorrShifted);
.DivResDenorm, .DivDenormShift, .DivOp, .DivCalcExpM,
.CorrDivExp, .SumZero, .Shifted, .SumExp, .CorrShifted);
///////////////////////////////////////////////////////////////////////////////
// Rounding