Re: long double data type
Re: long double data type
- Subject: Re: long double data type
- From: Luigi Castelli <email@hidden>
- Date: Tue, 15 Jun 2010 14:13:43 -0700 (PDT)
Thank you for your replies Ian and Stephen.
This is exactly what I am after...
> "On Intel macs, the type long double corresponds to IEEE-754 double
> extended precision. A double extended number is represented in 80 bits,
> and has a precision of 64 significant bits, roughly like 19 significant
> decimal digits. 15 bits are used to encode the exponent, which gives an
> exponent range from -16383 to 16384, inclusive."
Yes, that's what I learnt too, however I have also come across information similar to what Ian mentioned.
> There are no 80 bit floating point data types.
However from what "man float" says, the long double data type defines exactly an 80 bit type.
The two pieces of information seem to contradict each other.
I am trying to avoid software emulation for bigger types, if I can get away with native types.
To summarize: if it is true that computations can be performed natively with a maximum accuracy of 80 bits (64 bit effective resolution),
AND
it is all IEE compliant because computations are performed in the SSE unit, I will go for it.
However I am still not sure that's the case...
- Luigi
--- On Tue, 6/15/10, Stephen Davis <email@hidden> wrote:
> From: Stephen Davis <email@hidden>
> Subject: Re: long double data type
> To: "Luigi Castelli" <email@hidden>
> Cc: email@hidden
> Date: Tuesday, June 15, 2010, 1:15 PM
> On Jun 15, 2010, at 10:44 AM, Luigi
> Castelli wrote:
>
> > Hi there,
> >
> > this is the second time that I get a similar
> response:
> >
> >> Are you sure that your DSP approach is sound?
> >>
> >> If 64bits are not enough there is probably
> something wrong
> >> with your algorithm.
> >
> > I really don't want to sound arrogant because it is
> not what I am about, however I ASSURE you that I performed
> all the necessary tests, both mathematical and auditive to
> corroborate my conclusion. My approach is sound, I just
> don't have enough bits for the audio quality I am after. I
> understand it might sound weird to hear that 64 bits are not
> enough.
> > I might have reached the upper limit of the current
> technology, but doubting my approach is not helping. I would
> ask advice on the approach if I wasn't sure it was the right
> one.
> >
> > I would love to get back on track with the questions I
> have asked.
> > I apologize in advance if I offended somebody. It was
> not my intention.
> >
> > Thank you for your understanding.
> >
> > - Luigi
>
> Tahome, personally I found your comment a bit rude and a
> non-answer to the original question. To paraphrase the
> old adage, "If you don't have anything useful to add, don't
> say anything." Let's keep the responses in the helpful
> category, not in the flame-bait category.
>
> From "man float":
>
> "On Intel macs, the type long double corresponds to
> IEEE-754 double extended precision. A double extended
> number is represented in 80 bits, and has a precision of 64
> significant bits, roughly like 19 significant decimal
> digits. 15 bits are used to encode the exponent, which
> gives an exponent range from -16383 to 16384, inclusive."
>
> This is a direct mapping to the x86 (technically x87) FPU
> hardware which has always been 80 bits. Note that, on
> Mac OS X (intel) systems, single and double precision
> floating point math is normally executed in the SSE unit,
> not the x87 FPU.
>
> hth,
> stephen
>
> >
> >
> > --- On Tue, 6/15/10, tahome izwah <email@hidden>
> wrote:
> >
> >> From: tahome izwah <email@hidden>
> >> Subject: Re: long double data type
> >> To: email@hidden
> >> Date: Tuesday, June 15, 2010, 8:33 AM
> >> I know that I am not really
> >> contributing, but...
> >>
> >>> (Yes, I did my tests and 64 bits of precision
> just
> >> doesn't cut it)
> >>
> >> Are you sure that your DSP approach is sound?
> >>
> >> If 64bits are not enough there is probably
> something wrong
> >> with your algorithm.
> >>
> >> Just my 2 centibits
> >> --th
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