Re: ... replacement for 14.4 and C6.2 (interchange encodings)
Vincent,
> > The conversion of interval encoding doesn't not necessarily
> > reversing entire octet sequence.
> > It reverses subsequence related to inf and subsequence related to sup.
>
> That's why it cannot be a conversion from the bit string, otherwise
> the internal structure is lost (a bit string doesn't have an inf
> part and a sup part).
This is a parameterized mapping. One of its parameters is
the width of floating-point interchange format.
So this mapping "knows" about inf and sup part.
I think that it is better to keep IEEE 754 levels 1-4 and to add "Level 5"
than to modify Level 4. Otherwise we might have more objections.
-Dima
----- Original Message -----
From: vincent@xxxxxxxxxx
To: stds-1788@xxxxxxxxxxxxxxxxx
Sent: Thursday, June 26, 2014 5:50:29 PM GMT +04:00 Abu Dhabi / Muscat
Subject: Re: ... replacement for 14.4 and C6.2 (interchange encodings)
On 2014-06-26 05:50:03 -0700, Dmitry Nadezhin wrote:
> Vincent,
>
> > > Export and import of interchange formats normally occurs as a stream
> > > of octets (8-bit bytes), e.g. in a file or a network packet. There
> > > is therefore a need to define the mapping of the conceptual Level 4
> > > bit strings (as specified by 754-2008) and of the small integers used
> > > to encode decorations (out of scope for 754-2008) into a sequence of
> > > octets. There is also the fact that 754-2008 defines two distinct
> > > encodings of decimal formats, called BID and DPD.
> >
> > I don't think that you want to do that (convert bit strings),
> > otherwise (inf,sup) could be reversed by the change of endianness
> > on the bit string. The endianness should apply on words (thus this
> > is a conversion from the Level 3 representation), not on the whole
> > bit string.
>
> The conversion of interval encoding doesn't not necessarily
> reversing entire octet sequence.
> It reverses subsequence related to inf and subsequence related to sup.
That's why it cannot be a conversion from the bit string, otherwise
the internal structure is lost (a bit string doesn't have an inf
part and a sup part).
> I thought that usualy encoding of floating-point datum is reverted as a whole.
> If this is not true and it is reverted by words, there is a word
> "mixed-endian" later in the text.
By "word", I meant the encoding of the FP datum (64-bit for binary64,
128-bit for binary128...).
--
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)