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removed the +1 in the cvt

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This commit is contained in:
Katherine Parry 2022-07-13 09:41:35 -07:00
parent e05b2a07d2
commit 26e39dd325
1 changed files with 13 additions and 11 deletions
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24
pipelined/src/fpu/fcvt.sv
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@ -68,7 +68,8 @@ module fcvt (
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 [`LOGCVTLEN-1:0] LeadingZeros; // output from the LZC
logic [`CVTLEN:0] LzcInFull; // input to the Leading Zero Counter (priority encoder)
logic [`LOGCVTLEN-1:0] LeadingZeros; // output from the LZC
// seperate OpCtrl for code readability
@ -102,10 +103,11 @@ module fcvt (
// 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 ? {TrimInt, {`CVTLEN-`XLEN{1'b0}}} :
{Xm[`NF-1:0], {`CVTLEN-`NF{1'b0}}};
assign LzcInFull = IntToFp ? {1'b0, TrimInt, {`CVTLEN-`XLEN{1'b0}}} :
{Xm, {`CVTLEN-`NF{1'b0}}};
assign LzcIn = LzcInFull[`CVTLEN-1:0];
lzc #(`CVTLEN) lzc (.num(LzcIn), .ZeroCnt(LeadingZeros));
lzc #(`CVTLEN+1) lzc (.num(LzcInFull), .ZeroCnt(LeadingZeros));
///////////////////////////////////////////////////////////////////////////
// shifter
@ -119,13 +121,13 @@ module fcvt (
// denormalized/undeflowed result fp -> fp:
// - shift left by NF-1+CalcExp - to shift till the biased expoenent is 0
// ??? -> fp:
// - shift left by LeadingZeros+1 - to shift till the result is normalized
// - shift left by LeadingZeros - 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 ? Ce[`LOGCVTLEN-1:0]&{`LOGCVTLEN{~Ce[`NE]}} :
ResDenormUf&~IntToFp ? (`LOGCVTLEN)'(`NF-1)+Ce[`LOGCVTLEN-1:0] :
(LeadingZeros+1)&{`LOGCVTLEN{XDenorm|IntToFp}};
(LeadingZeros)&{`LOGCVTLEN{XDenorm|IntToFp}};
///////////////////////////////////////////////////////////////////////////
// exp calculations
@ -197,14 +199,14 @@ module fcvt (
// | 0's | Mantissa | 0's if nessisary |
// | keep |
//
// - if the input is denormalized then we dont shift... so the "- (LeadingZeros+1)" is just leftovers from other options
// int -> fp : largest bias + XLEN - Largest bias + new bias - 1 - LeadingZeros = XLEN + NewBias - 1 - LeadingZeros
// - if the input is denormalized then we dont shift... so the "- LeadingZeros" is just leftovers from other options
// int -> fp : largest bias + XLEN - Largest bias + new bias - LeadingZeros = XLEN + NewBias - LeadingZeros
// Process:
// - shifted right by XLEN (XLEN)
// - shift left to normilize (-1-LeadingZeros)
// - shift left to normilize (-LeadingZeros)
// - newBias to make the biased exponent
// oldexp - biasold +newbias - (LeadingZeros+1)&(XDenorm|IntToFp)
assign Ce = {1'b0, OldExp} - (`NE+1)'(`BIAS) + {2'b0, NewBias} - {{`NE{1'b0}}, XDenorm|IntToFp} - {{`NE-`LOGCVTLEN+1{1'b0}}, (LeadingZeros&{`LOGCVTLEN{XDenorm|IntToFp}})};
// oldexp - biasold +newbias - LeadingZeros&(XDenorm|IntToFp)
assign Ce = {1'b0, OldExp} - (`NE+1)'(`BIAS) + {2'b0, NewBias} - {{`NE-`LOGCVTLEN+1{1'b0}}, (LeadingZeros&{`LOGCVTLEN{XDenorm|IntToFp}})};
// find if the result is dnormal or underflows
// - if Calculated expoenent is 0 or negitive (and the input/result is not exactaly 0)
// - can't underflow an integer to Fp conversion