forked from Github_Repos/cvw
69 lines
3.2 KiB
Systemverilog
69 lines
3.2 KiB
Systemverilog
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`include "wally-config.vh"
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module cvtshiftcalc(
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input logic XZeroM,
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input logic ToInt,
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input logic IntToFp,
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input logic [`NE:0] CvtCalcExpM, // the calculated expoent
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input logic [`NF:0] XManM, // input mantissas
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input logic [`FMTBITS-1:0] OutFmt, // output format
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input logic [`LGLEN-1:0] CvtLzcInM, // input to the Leading Zero Counter (priority encoder)
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input logic CvtResDenormUfM,
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output logic CvtResUf,
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output logic [`LGLEN+`NF:0] CvtShiftIn // number to be shifted
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);
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logic [$clog2(`NF):0] ResNegNF; // the result's fraction length negated (-NF)
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///////////////////////////////////////////////////////////////////////////
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// shifter
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///////////////////////////////////////////////////////////////////////////
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// seclect the input to the shifter
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// fp -> int:
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// | `XLEN zeros | Mantissa | 0's if nessisary |
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// Other problems:
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// - if shifting to the right (neg CalcExp) then don't a 1 in the round bit (to prevent an incorrect plus 1 later durring rounding)
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// - we do however want to keep the one in the sticky bit so set one of bits in the sticky bit area to 1
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// - ex: for the case 0010000.... (double)
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// ??? -> fp:
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// - if result is denormalized or underflowed then we want to shift right i.e. shift right then shift left:
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// | `NF-1 zeros | Mantissa | 0's if nessisary |
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// - otherwise:
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// | LzcInM | 0's if nessisary |
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assign CvtShiftIn = ToInt ? {{`XLEN{1'b0}}, XManM[`NF]&~CvtCalcExpM[`NE], XManM[`NF-1]|(CvtCalcExpM[`NE]&XManM[`NF]), XManM[`NF-2:0], {`LGLEN-`XLEN{1'b0}}} :
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CvtResDenormUfM ? {{`NF-1{1'b0}}, XManM, {`LGLEN-`NF+1{1'b0}}} :
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{CvtLzcInM, {`NF+1{1'b0}}};
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// choose the negative of the fraction size
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if (`FPSIZES == 1) begin
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assign ResNegNF = -($clog2(`NF)+1)'(`NF);
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end else if (`FPSIZES == 2) begin
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assign ResNegNF = OutFmt ? -($clog2(`NF)+1)'(`NF) : -($clog2(`NF)+1)'(`NF1);
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end else if (`FPSIZES == 3) begin
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always_comb
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case (OutFmt)
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`FMT: ResNegNF = -($clog2(`NF)+1)'(`NF);
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`FMT1: ResNegNF = -($clog2(`NF)+1)'(`NF1);
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`FMT2: ResNegNF = -($clog2(`NF)+1)'(`NF2);
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default: ResNegNF = 1'bx;
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endcase
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end else if (`FPSIZES == 4) begin
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always_comb
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case (OutFmt)
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2'h3: ResNegNF = -($clog2(`NF)+1)'(`Q_NF);
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2'h1: ResNegNF = -($clog2(`NF)+1)'(`D_NF);
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2'h0: ResNegNF = -($clog2(`NF)+1)'(`S_NF);
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2'h2: ResNegNF = -($clog2(`NF)+1)'(`H_NF);
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endcase
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end
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// determine if the result underflows ??? -> fp
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// - if the first 1 is shifted out of the result then the result underflows
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// - can't underflow an integer to fp conversions
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assign CvtResUf = ($signed(CvtCalcExpM) < $signed({{`NE-$clog2(`NF){1'b1}}, ResNegNF}))&~XZeroM&~IntToFp;
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endmodule
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