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137 lines
7.1 KiB
Systemverilog
137 lines
7.1 KiB
Systemverilog
///////////////////////////////////////////
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// fmashiftcalc.sv
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//
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// Written: me@KatherineParry.com
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// Modified: 7/5/2022
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//
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// Purpose: FMA shift calculation
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//
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// Documentation: RISC-V System on Chip Design Chapter 13
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//
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// A component of the CORE-V-WALLY configurable RISC-V project.
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// https://github.com/openhwgroup/cvw
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//
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// Copyright (C) 2021-23 Harvey Mudd College & Oklahoma State University
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//
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// SPDX-License-Identifier: Apache-2.0 WITH SHL-2.1
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//
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// Licensed under the Solderpad Hardware License v 2.1 (the “License”); you may not use this file
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// except in compliance with the License, or, at your option, the Apache License version 2.0. You
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// may obtain a copy of the License at
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//
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// https://solderpad.org/licenses/SHL-2.1/
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//
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// Unless required by applicable law or agreed to in writing, any work distributed under the
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// License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
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// either express or implied. See the License for the specific language governing permissions
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// and limitations under the License.
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////////////////////////////////////////////////////////////////////////////////////////////////
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module fmashiftcalc import cvw::*; #(parameter cvw_t P) (
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input logic [P.FMTBITS-1:0] Fmt, // precision 1 = double 0 = single
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input logic [P.NE+1:0] FmaSe, // sum's exponent
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input logic [3*P.NF+3:0] FmaSm, // the positive sum
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input logic [$clog2(3*P.NF+5)-1:0] FmaSCnt, // normalization shift count
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output logic [P.NE+1:0] NormSumExp, // exponent of the normalized sum not taking into account Subnormal or zero results
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output logic FmaSZero, // is the result subnormal - calculated before LZA corection
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output logic FmaPreResultSubnorm, // is the result subnormal - calculated before LZA corection
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output logic [$clog2(3*P.NF+5)-1:0] FmaShiftAmt, // normalization shift count
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output logic [3*P.NF+5:0] FmaShiftIn // is the sum zero
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);
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logic [P.NE+1:0] PreNormSumExp; // the exponent of the normalized sum with the P.FLEN bias
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logic [P.NE+1:0] BiasCorr; // correction for bias
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///////////////////////////////////////////////////////////////////////////////
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// Normalization
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///////////////////////////////////////////////////////////////////////////////
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// Determine if the sum is zero
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assign FmaSZero = ~(|FmaSm);
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// calculate the sum's exponent
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assign PreNormSumExp = FmaSe + {{P.NE+2-$unsigned($clog2(3*P.NF+5)){1'b1}}, ~FmaSCnt} + (P.NE+2)'(P.NF+3);
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//convert the sum's exponent into the proper precision
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if (P.FPSIZES == 1) begin
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assign NormSumExp = PreNormSumExp;
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end else if (P.FPSIZES == 2) begin
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assign BiasCorr = Fmt ? (P.NE+2)'(0) : (P.NE+2)'(P.BIAS1-P.BIAS);
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assign NormSumExp = PreNormSumExp+BiasCorr;
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end else if (P.FPSIZES == 3) begin
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always_comb begin
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case (Fmt)
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P.FMT: BiasCorr = 0;
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P.FMT1: BiasCorr = (P.NE+2)'(P.BIAS1-P.BIAS);
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P.FMT2: BiasCorr = (P.NE+2)'(P.BIAS2-P.BIAS);
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default: BiasCorr = 'x;
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endcase
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end
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assign NormSumExp = PreNormSumExp+BiasCorr;
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end else if (P.FPSIZES == 4) begin
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always_comb begin
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case (Fmt)
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2'h3: BiasCorr = 0;
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2'h1: BiasCorr = (P.NE+2)'(P.D_BIAS-P.Q_BIAS);
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2'h0: BiasCorr = (P.NE+2)'(P.S_BIAS-P.Q_BIAS);
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2'h2: BiasCorr = (P.NE+2)'(P.H_BIAS-P.Q_BIAS);
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endcase
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end
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assign NormSumExp = PreNormSumExp+BiasCorr;
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end
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// determine if the result is subnormal: (NormSumExp <= 0) & (NormSumExp >= -FracLen) & ~FmaSZero
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if (P.FPSIZES == 1) begin
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logic Sum0LEZ, Sum0GEFL;
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assign Sum0LEZ = PreNormSumExp[P.NE+1] | ~|PreNormSumExp;
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assign Sum0GEFL = $signed(PreNormSumExp) >= $signed((P.NE+2)'(-P.NF-2));
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assign FmaPreResultSubnorm = Sum0LEZ & Sum0GEFL & ~FmaSZero;
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end else if (P.FPSIZES == 2) begin
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logic Sum0LEZ, Sum0GEFL, Sum1LEZ, Sum1GEFL;
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assign Sum0LEZ = PreNormSumExp[P.NE+1] | ~|PreNormSumExp;
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assign Sum0GEFL = $signed(PreNormSumExp) >= $signed((P.NE+2)'(-P.NF-2));
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assign Sum1LEZ = $signed(PreNormSumExp) <= $signed((P.NE+2)'(P.BIAS-P.BIAS1));
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assign Sum1GEFL = $signed(PreNormSumExp) >= $signed((P.NE+2)'(-P.NF1-2+P.BIAS-P.BIAS1)) | ~|PreNormSumExp;
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assign FmaPreResultSubnorm = (Fmt ? Sum0LEZ : Sum1LEZ) & (Fmt ? Sum0GEFL : Sum1GEFL) & ~FmaSZero;
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end else if (P.FPSIZES == 3) begin
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logic Sum0LEZ, Sum0GEFL, Sum1LEZ, Sum1GEFL, Sum2LEZ, Sum2GEFL;
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assign Sum0LEZ = PreNormSumExp[P.NE+1] | ~|PreNormSumExp;
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assign Sum0GEFL = $signed(PreNormSumExp) >= $signed((P.NE+2)'(-P.NF-2));
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assign Sum1LEZ = $signed(PreNormSumExp) <= $signed((P.NE+2)'(P.BIAS-P.BIAS1));
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assign Sum1GEFL = $signed(PreNormSumExp) >= $signed((P.NE+2)'(-P.NF1-2+P.BIAS-P.BIAS1)) | ~|PreNormSumExp;
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assign Sum2LEZ = $signed(PreNormSumExp) <= $signed((P.NE+2)'(P.BIAS-P.BIAS2));
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assign Sum2GEFL = $signed(PreNormSumExp) >= $signed((P.NE+2)'(-P.NF2-2+P.BIAS-P.BIAS2)) | ~|PreNormSumExp;
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always_comb begin
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case (Fmt)
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P.FMT: FmaPreResultSubnorm = Sum0LEZ & Sum0GEFL; // & ~FmaSZero; // checking sum is not zero is harmless but turns out to be unnecessary
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P.FMT1: FmaPreResultSubnorm = Sum1LEZ & Sum1GEFL; // & ~FmaSZero;
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P.FMT2: FmaPreResultSubnorm = Sum2LEZ & Sum2GEFL; // & ~FmaSZero;
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default: FmaPreResultSubnorm = 1'bx;
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endcase
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end
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end else if (P.FPSIZES == 4) begin
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logic Sum0LEZ, Sum0GEFL, Sum1LEZ, Sum1GEFL, Sum2LEZ, Sum2GEFL, Sum3LEZ, Sum3GEFL;
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assign Sum0LEZ = PreNormSumExp[P.NE+1] | ~|PreNormSumExp;
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assign Sum0GEFL = $signed(PreNormSumExp) >= $signed((P.NE+2)'(-P.NF-2));
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assign Sum1LEZ = $signed(PreNormSumExp) <= $signed((P.NE+2)'(P.BIAS-P.D_BIAS));
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assign Sum1GEFL = $signed(PreNormSumExp) >= $signed((P.NE+2)'(-P.D_NF-2+P.BIAS-P.D_BIAS)) | ~|PreNormSumExp;
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assign Sum2LEZ = $signed(PreNormSumExp) <= $signed((P.NE+2)'(P.BIAS-P.S_BIAS));
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assign Sum2GEFL = $signed(PreNormSumExp) >= $signed((P.NE+2)'(-P.S_NF-2+P.BIAS-P.S_BIAS)) | ~|PreNormSumExp;
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assign Sum3LEZ = $signed(PreNormSumExp) <= $signed((P.NE+2)'(P.BIAS-P.H_BIAS));
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assign Sum3GEFL = $signed(PreNormSumExp) >= $signed((P.NE+2)'(-P.H_NF-2+P.BIAS-P.H_BIAS)) | ~|PreNormSumExp;
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always_comb begin
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case (Fmt)
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2'h3: FmaPreResultSubnorm = Sum0LEZ & Sum0GEFL & ~FmaSZero;
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2'h1: FmaPreResultSubnorm = Sum1LEZ & Sum1GEFL & ~FmaSZero;
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2'h0: FmaPreResultSubnorm = Sum2LEZ & Sum2GEFL & ~FmaSZero;
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2'h2: FmaPreResultSubnorm = Sum3LEZ & Sum3GEFL & ~FmaSZero;
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endcase
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end
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end
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// set and calculate the shift input and amount
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// - shift once if killing a product and the result is subnormal
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assign FmaShiftIn = {2'b0, FmaSm};
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if (P.FPSIZES == 1) assign FmaShiftAmt = FmaPreResultSubnorm ? FmaSe[$clog2(3*P.NF+5)-1:0]+($clog2(3*P.NF+5))'(P.NF+2): FmaSCnt+1;
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else assign FmaShiftAmt = FmaPreResultSubnorm ? FmaSe[$clog2(3*P.NF+5)-1:0]+($clog2(3*P.NF+5))'(P.NF+2)+BiasCorr[$clog2(3*P.NF+5)-1:0]: FmaSCnt+1;
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endmodule
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