`include "wally-config.vh" // largest length in IEU/FPU `define LGLEN ((`NF<`XLEN) ? `XLEN : `NF) module fcvt ( input logic XSgnE, // input's sign input logic [`NE-1:0] XExpE, // input's exponent input logic [`NF:0] XManE, // input's fraction input logic [`XLEN-1:0] ForwardedSrcAE, // integer input - from IEU input logic [2:0] FOpCtrlE, // choose which opperation (look below for values) input logic FWriteIntE, // is fp->int (since it's writting to the integer register) input logic XZeroE, // is the input zero input logic XOrigDenormE, // is the input denormalized input logic XInfE, // is the input infinity input logic XNaNE, // is the input a NaN input logic XSNaNE, // is the input a signaling NaN input logic [2:0] FrmE, // rounding mode 000 = rount to nearest, ties to even 001 = round twords zero 010 = round down 011 = round up 100 = round to nearest, ties to max magnitude input logic [`FPSIZES/3:0] FmtE, // the input's precision (11=quad 01=double 00=single 10=half) output logic [`FLEN-1:0] CvtResE, // the fp to fp conversion's result output logic [`XLEN-1:0] CvtIntResE, // the fp to fp conversion's result output logic [4:0] CvtFlgE // the fp to fp conversion's flags ); // OpCtrls: // fp->fp conversions: {0, output precision} - only one of the operations writes to the int register // half - 10 // single - 00 // double - 01 // quad - 11 // int<->fp conversions: {is int->fp?, is the integer 64-bit?, is the integer signed?} // bit 2 bit 1 bit 0 // for example: signed long -> single floating point has the OpCode 101 // (FF) fp -> fp coversion signals // (IF) int -> fp coversion signals // (FI) fp -> int coversion signals logic [`FPSIZES/3:0] OutFmt; // format of the output logic [`XLEN-1:0] PosInt; // the positive integer input logic [`LGLEN-1:0] LzcIn; // input to the Leading Zero Counter (priority encoder) logic [`NE:0] CalcExp; // the calculated expoent logic [$clog2(`LGLEN):0] ShiftAmt; // how much to shift by logic [`LGLEN+`NF:0] ShiftIn; // number to be shifted logic ResDenormUf;// does the result underflow or is denormalized logic ResUf; // does the result underflow logic [`LGLEN+`NF:0] Shifted; // the shifted result logic [`NE-2:0] NewBias; // the bias of the final result logic [$clog2(`NF):0] ResNegNF; // the result's fraction length negated (-NF) logic [`NE-1:0] OldExp; // the old exponent logic ResSgn; // the result's sign logic Sticky; // sticky bit - for rounding logic Round; // round bit - for rounding logic LSBFrac; // the least significant bit of the fraction - for rounding logic CalcPlus1; // the calculated plus 1 logic Plus1; // add one to the final result? logic [`FLEN-1:0] ShiftedPlus1; // plus one shifted to the proper position logic [`NE:0] FullResExp; // the full result exponent (with the overflow bit) logic [`NE-1:0] ResExp; // the result's exponent (trimmed to the correct size) logic [`NF-1:0] ResFrac; // the result's fraction logic [`XLEN+1:0] NegRes; // the negation of the result logic [`XLEN-1:0] OfIntRes; // the overflow result for integer output logic Overflow, Underflow, Inexact, Invalid; // flags logic IntInexact, FpInexact, IntInvalid, FpInvalid; // flags for FP and int outputs logic [`NE-1:0] MaxExp; // the maximum exponent before overflow logic [1:0] NegResMSBS; // the negitive integer result's most significant bits logic [`FLEN-1:0] NaNRes, InfRes, Res, UfRes; //various special results logic KillRes; // kill the result? logic Signed; // is the opperation with a signed integer? logic Int64; // is the integer 64 bits? logic IntToFp; // is the opperation an int->fp conversion? logic ToInt; // is the opperation an fp->int conversion? // seperate OpCtrl for code readability assign Signed = FOpCtrlE[0]; assign Int64 = FOpCtrlE[1]; assign IntToFp = FOpCtrlE[2]; assign ToInt = FWriteIntE; // choose the ouptut format depending on the opperation // - fp -> fp: OpCtrl contains the percision of the output // - int -> fp: FmtE contains the percision of the output assign OutFmt = IntToFp ? FmtE : (FOpCtrlE[1:0] == `FMT); /////////////////////////////////////////////////////////////////////////// // negation /////////////////////////////////////////////////////////////////////////// // negate the input if the input is a negitive singed integer // - remove leading ones if the input is a unsigned 32-bit integer // // Negitive input // 64-bit input : negate the input // 32-bit input : trim to 32-bits and negate the input // Positive input // 64-bit input : do nothing // 32-bit input : trim to 32-bits assign PosInt = ResSgn ? Int64 ? -ForwardedSrcAE : {{`XLEN-32{1'b0}}, -ForwardedSrcAE[31:0]} : Int64 ? ForwardedSrcAE : {{`XLEN-32{1'b0}}, ForwardedSrcAE[31:0]}; /////////////////////////////////////////////////////////////////////////// // lzc /////////////////////////////////////////////////////////////////////////// // choose the input to the leading zero counter i.e. priority encoder // int -> fp : | positive integer | 00000... (if needed) | // fp -> fp : | fraction | 00000... (if needed) | assign LzcIn = IntToFp ? {PosInt, {`LGLEN-`XLEN{1'b0}}} : // I->F {XManE[`NF-1:0], {`LGLEN-`NF{1'b0}}}; // F->F // lglen is the largest possible value of ZeroCnt (NF or XLEN) hence normcnt must be log2(lglen) bits logic [$clog2(`LGLEN):0] i, ZeroCnt; always_comb begin i = 0; while (~LzcIn[`LGLEN-1-i] & i <= `LGLEN-1) i = i+1; // search for leading one ZeroCnt = i; end /////////////////////////////////////////////////////////////////////////// // shifter /////////////////////////////////////////////////////////////////////////// // F->F shift so the fraction is not denormalized // Large->Small Denrom -> Norm Frac: // // | Frac | `NF zeros| << ShiftCnt // // Small->Large Norm -> Denorm Frac: // - shift right so that the new-bias exponet = 1 // - so shift right by new-bias - 1 exponent // - ie shift left by NF - 1 + new-bias exponent (if this is negitive then 0 is selected as a result later) // - new-bias exponent is negitive // // | `NF-1 zeros |1| Frac | << NF + new-bias exponent // | keep | // // Int -> Fp : // | Int | `NF zeros| << ShiftCnt // Fp -> Int : // | `XLEN zeros | Man | << CalcExp // seclect the input to the shifter // fp -> int: // | `XLEN zeros | Mantissa | 0's if nessisary | // Other problems: // - 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) // - we do however want to keep the one in the sticky bit so set one of bits in the sticky bit area to 1 // - ex: for the case 0010000.... (double) // ??? -> fp: // - if result is denormalized or underflowed then we want to normalize the result: // | `NF zeros | Mantissa | 0's if nessisary | // - otherwise: // | lzcIn | 0's if nessisary | assign ShiftIn = ToInt ? {{`XLEN{1'b0}}, XManE[`NF]&~CalcExp[`NE], XManE[`NF-1]|(CalcExp[`NE]&XManE[`NF]), XManE[`NF-2:0], {`LGLEN-`XLEN{1'b0}}} : ResDenormUf ? {{`NF-1{1'b0}}, XManE, {`LGLEN-`NF+1{1'b0}}} : {LzcIn, {`NF+1{1'b0}}}; // kill the shift if it's negitive // select the amount to shift by // fp -> int: // - shift left by CalcExp - essentially shifting until the unbiased exponent = 0 // - don't shift if supposed to shift right (underflowed or denorm input) // denormalized/undeflowed result fp -> fp: // - shift left by NF-1+CalcExp - to shift till the biased expoenent is 0 // ??? -> fp: // - shift left by ZeroCnt+1 - to shift till the result is normalized // - only shift fp -> fp if the intital value is denormalized // - this is a problem because the input to the lzc was the fraction rather than the mantissa // - rather have a few and-gates than an extra bit in the priority encoder??? *** is this true? assign ShiftAmt = ToInt ? CalcExp[$clog2(`LGLEN):0]&{$clog2(`LGLEN)+1{~CalcExp[`NE]}} : ResDenormUf&~IntToFp ? ($clog2(`LGLEN)+1)'(`NF-1)+CalcExp[$clog2(`LGLEN):0] : (ZeroCnt+1)&{$clog2(`LGLEN)+1{XOrigDenormE|IntToFp}}; // shift assign Shifted = ShiftIn << ShiftAmt; /////////////////////////////////////////////////////////////////////////// // exp calculations /////////////////////////////////////////////////////////////////////////// // fp -> int // CalcExp = 1 - largest bias + 1 - // *** possible optimizaations: // - if subtracting exp by bias only the msb needs a full adder, the rest can be HA - dunno how to implement this for synth // - Smaller exp -> Larger Exp can be calculated with: *** can use in Other units??? FMA??? insert this thing in later // Exp if in range: {~Exp[SNE-1], Exp[SNE-2:0]} // Exp in range if: Exp[SNE-1] = 1 & Exp[LNE-2:SNE] = 1111... & Exp[LNE-1] = 0 | Exp[SNE-1] = 0 & Exp[LNE-2:SNE] = 000... & Exp[LNE-1] = 1 // i.e.: &Exp[LNE-2:SNE-1] xor Exp[LNE-1] // Too big if: Exp[LNE-1] = 1 // Too small if: none of the above // Select the bias of the output // fp -> int : select 1 // ??? -> fp : pick the new bias depending on the output format assign NewBias = ToInt ? (`NE-1)'(1) : OutFmt ? (`NE-1)'(`BIAS) : (`NE-1)'(`BIAS1); // select the old exponent // int -> fp : largest bias + XLEN // fp -> ??? : XExp assign OldExp = IntToFp ? (`NE)'(`BIAS)+(`NE)'(`XLEN) : XExpE; // calculate CalcExp // fp -> fp : // - XExp - Largest bias + new bias // fp -> int : XExp // int -> fp : largest bias + XLEN // the -XOrigDenorm is to take into account the correction (which had a plus 1) assign CalcExp = {1'b0, OldExp} - (`NE+1)'(`BIAS) + {2'b0, NewBias} - {{`NE{1'b0}}, XOrigDenormE|IntToFp} - {{`NE-$clog2(`LGLEN){1'b0}}, (ZeroCnt&{$clog2(`LGLEN)+1{XOrigDenormE|IntToFp}})}; // if result is 0 or negitive assign ResDenormUf = (~|CalcExp | CalcExp[`NE])&~XZeroE; assign ResNegNF = (FOpCtrlE[1:0] == `FMT) ? -`NF : -`NF1; // if the reuslt underflows and somthing is shifted out set the sticky bit assign ResUf = ($signed(CalcExp) < $signed({{`NE-$clog2(`NF){1'b1}}, ResNegNF}))&~XZeroE; /////////////////////////////////////////////////////////////////////////// // sign /////////////////////////////////////////////////////////////////////////// assign ResSgn = IntToFp ? Int64 ? ForwardedSrcAE[`XLEN-1]&Signed : ForwardedSrcAE[31]&Signed : XSgnE; /////////////////////////////////////////////////////////////////////////// // rounding /////////////////////////////////////////////////////////////////////////// // round to nearest even // {Round, Sticky} // 0x - do nothing // 10 - tie - Plus1 if result is odd (LSBNormSum = 1) // 11 - Plus1 // round to zero - do nothing // round to -infinity - Plus1 if negative // round to infinity - Plus1 if positive // round to nearest max magnitude // {Guard, Round, Sticky} // 0x - do nothing // 1x - Plus1 // ResUf is used when a fp->fp result underflows but all the bits get shifted out, leaving nothing for the sticky bit assign Sticky = ToInt ? |Shifted[`LGLEN+`NF-`XLEN-1:0] : (OutFmt ? |Shifted[`LGLEN+`NF-`NF-1:0] : |Shifted[`LGLEN+`NF-`NF1-1:0])|ResUf; assign Round = ToInt ? Shifted[`LGLEN+`NF-`XLEN] : OutFmt ? Shifted[`LGLEN+`NF-`NF] : |Shifted[`LGLEN+`NF-`NF1]; assign LSBFrac = ToInt ? Shifted[`LGLEN+`NF-`XLEN+1] : OutFmt ? Shifted[`LGLEN+`NF-`NF+1] : Shifted[`LGLEN+`NF-`NF1+1]; always_comb begin // ***remove guard bit // Determine if you add 1 case (FrmE) 3'b000: CalcPlus1 = Round & (Sticky | LSBFrac);//round to nearest even 3'b001: CalcPlus1 = 0;//round to zero 3'b010: CalcPlus1 = ResSgn;//round down 3'b011: CalcPlus1 = ~ResSgn;//round up 3'b100: CalcPlus1 = Round;//round to nearest max magnitude default: CalcPlus1 = 1'bx; endcase end assign Plus1 = CalcPlus1&(Round|Sticky); assign ShiftedPlus1 = OutFmt ? {{`FLEN-1{1'b0}},Plus1} : {{`NE+`NF1{1'b0}}, Plus1, {`FLEN-`NE-`NF1-1{1'b0}}}; // kill calcExp if the result is denormalized assign {FullResExp, ResFrac} = {CalcExp&{`NE+1{~ResDenormUf}}, Shifted[`LGLEN+`NF:`LGLEN+`NF+1-`NF]} + ShiftedPlus1; assign ResExp = FullResExp[`NE-1:0]; /////////////////////////////////////////////////////////////////////////// // flags /////////////////////////////////////////////////////////////////////////// // calculate the flags // dont set underflow overflow or inexact flags if result is NaN assign MaxExp = ToInt ? Int64 ? 65 : 33 : OutFmt ? {`NE{1'b1}} : {{`NE-`NE1{1'b0}}, {`NE1{1'b1}}}; // if the exponent is lager or equal to the maximum and it's not negitive // F->F if the input is inf then the output is also Inf ie exact, so dont set the underflow flag // if the result exponent is larger then the maximum possible exponent // | and the exponent is positive // | | and the input is not NaN or Infinity // | | | assign Overflow = ((ResExp >= MaxExp)&~CalcExp[`NE]&~(XNaNE|XInfE)); // only set the underflow flag if not-exact // set the underflow flag if the result is denomal or underflowed // can't underflow durring to integer conversions // if the result is denormalized or underflowed // | and the result did not round into normal values // | | and the result is not exact // | | | and the result isn't NaN // | | | | assign Underflow = ResDenormUf & ~(ResExp==1 & CalcExp == 0) & (Sticky|Round)&~(XNaNE); // we are using the IEEE convertToIntegerExact opperations (rather then the exact ones) which do singal the inexact flag // if there were bits thrown away // | if overflowed or underflowed // | | and if not a NaN // | | | assign FpInexact = (Sticky|Round|Underflow|Overflow)&(~XNaNE|IntToFp); // if the result is too small to be represented and not 0 // | and if the result is not invalid (outside the integer bounds) // | | assign IntInexact = ((CalcExp[`NE]&~XZeroE)|Sticky|Round)&~Invalid; assign Inexact = ToInt ? IntInexact : FpInexact; // if an input was a singaling NaN(and we're using a FP input) assign FpInvalid = (XSNaNE&~IntToFp); assign NegResMSBS = Signed ? Int64 ? NegRes[`XLEN:`XLEN-1] : NegRes[32:31] : Int64 ? NegRes[`XLEN+1:`XLEN] : NegRes[33:32]; // if the input is NaN or infinity // | if the integer result overflows (out of range) // | | if the input was negitive but ouputing to a unsigned number // | | | the result doesn't round to zero // | | | | or the result rounds up out of bounds // | | | | and the result didn't underflow // | | | | | assign IntInvalid = XNaNE|XInfE|Overflow|((XSgnE&~Signed)&(~((CalcExp[`NE]|(~|CalcExp))&~Plus1)))|(NegResMSBS[1]^NegResMSBS[0]); // | // or when the positive result rounds up out of range assign Invalid = ToInt ? IntInvalid : FpInvalid; // pack the flags together and choose the result based on the opperation // don't set the overflow or underfolw flags if converting to integer assign CvtFlgE = {Invalid, 1'b0, Overflow&~ToInt, Underflow&~ToInt, Inexact}; /////////////////////////////////////////////////////////////////////////// // result selection /////////////////////////////////////////////////////////////////////////// // when the input is zero for F->F the exponent is not calulated as 0 so combine with underflow result //logic [$clog2(`NF)-1:0] MinDenormExp; //assign MinDenormExp = FOpCtrlE[1:0] == `FMT ? -`NE : -`NE1; assign KillRes = (ResUf|(XZeroE&~IntToFp)|(~|PosInt&IntToFp)); //assign NaNRes = FOpCtrlE[1:0] == `FMT ? {1'b0, {`NE+1{1'b1}}, (`NF-1)'(0)} : {{`FLEN-`LEN1{1'b1}}, 1'b0, {`NE1+1{1'b1}}, (`NF1-1)'(0)}; if(`IEEE754) begin assign NaNRes = FOpCtrlE[1:0] == `FMT ? {1'b0, {`NE+1{1'b1}}, XManE[`NF-2:0]} : {{`FLEN-`LEN1{1'b1}}, 1'b0, {`NE1+1{1'b1}}, XManE[`NF-2:`NF-`NF1]}; end else begin assign NaNRes = FOpCtrlE[1:0] == `FMT ? {1'b0, {`NE+1{1'b1}}, {`NF-1{1'b0}}} : {{`FLEN-`LEN1{1'b1}}, 1'b0, {`NE1+1{1'b1}}, {`NF1-1{1'b0}}}; end // assign InfRes = FOpCtrlE[1:0] == `FMT ? {ResSgn, {`NE{1'b1}}, (`NF)'(0)} : {{`FLEN-`LEN1{1'b1}}, ResSgn, {`NE1{1'b1}}, (`NF1)'(0)}; // output one less then the maximum value if rounding down (RZ RU RD) // if infinitiy output infinity assign InfRes = FOpCtrlE[1:0] == `FMT ? ~XInfE&((FrmE[1:0]==2'b01) | (FrmE[1:0]==2'b10&~ResSgn) | (FrmE[1:0]==2'b11&ResSgn)) ? {ResSgn, {`NE-1{1'b1}}, 1'b0, {`NF{1'b1}}} : {ResSgn, {`NE{1'b1}}, {`NF{1'b0}}} : ~XInfE&((FrmE[1:0]==2'b01) | (FrmE[1:0]==2'b10&~ResSgn) | (FrmE[1:0]==2'b11&ResSgn)) ? {{`FLEN-`LEN1{1'b1}}, ResSgn, {`NE1-1{1'b1}}, 1'b0, {`NF1{1'b1}}} : {{`FLEN-`LEN1{1'b1}}, ResSgn, {`NE1{1'b1}}, (`NF1)'(0)}; // if RU/RD then round the underflowed result if needed // integer zero's exponent is not calculated corresctly so go through underflow result assign UfRes = OutFmt ? {ResSgn, (`FLEN-2)'(0), Plus1&FrmE[1]} : {{`FLEN-`LEN1{1'b1}}, ResSgn, (`LEN1-2)'(0), Plus1&FrmE[1]}; assign Res = OutFmt ? {ResSgn, ResExp, ResFrac} : {{`FLEN-`LEN1{1'b1}}, ResSgn, ResExp[`NE1-1:0], ResFrac[`NF-1:`NF-`NF1]}; assign CvtResE = XNaNE&~IntToFp ? NaNRes : (XInfE|Overflow)&~IntToFp ? InfRes : KillRes ? UfRes : Res; // *** probably can optimize the negation // NaNs sould ouput the same as a positive infinity // a 32bit unsigend result should be sign extended (as if it is not a unsigned number) assign OfIntRes = Signed ? XSgnE&~XNaNE ? Int64 ? {1'b1, {`XLEN-1{1'b0}}} : {{`XLEN-32{1'b1}}, 1'b1, {31{1'b0}}} : // signed negitive Int64 ? {1'b0, {`XLEN-1{1'b1}}} : {{`XLEN-32{1'b0}}, 1'b0, {31{1'b1}}} : // signed positive XSgnE&~XNaNE ? {`XLEN{1'b0}} : // unsigned negitive {`XLEN{1'b1}};// unsigned positive assign NegRes = XSgnE ? -({2'b0, Shifted[`LGLEN+`NF:`LGLEN+`NF+1-`XLEN]}+{{`XLEN+1{1'b0}},Plus1}) : {2'b0, Shifted[`LGLEN+`NF:`LGLEN+`NF+1-`XLEN]}+{{`XLEN+1{1'b0}},Plus1}; assign CvtIntResE = Invalid ? OfIntRes : CalcExp[`NE] ? XSgnE&Signed&Plus1 ? {{`XLEN{1'b1}}} : {{`XLEN-1{1'b0}}, Plus1} : //CalcExp has to come after invalid ***swap to actual mux at some point?? Int64 ? NegRes[`XLEN-1:0] : {{`XLEN-32{NegRes[31]}}, NegRes[31:0]}; endmodule