Re: Motion P1788/M0002.01_ProcessStructure YES
> Date: Mon, 23 Mar 2009 03:43:48 +0100
> From: Vincent Lefevre <vincent@xxxxxxxxxx>
> To: stds-1788 <stds-1788@xxxxxxxxxxxxxxxxx>
> Subject: Re: Motion P1788/M0002.01_ProcessStructure YES
>
> On 2009-03-16 08:48:54 -0700, Dan Zuras Intervals wrote:
> > First, those of you who are familiar with 754-1985 but not
> > 754-2008 should know that the new standard contains optional
> > support for arbitrary precision arithmetic.
>
> I don't know what you mean by "optional support for arbitrary
> precision arithmetic". But 754-2008 only defines fixed-width
> (and fixed-precision) formats. Arbitrary precision arithmetic
> (such as the one defined by the MPFR library) is out of the
> scope of the 754 standard (though there are many similarities).
>
> Anyway I don't see anything in Sections 1 and 2 that would be
> against arbitrary precision arithmetic, and...
>
> > So a vote for this proposal is not a vote against the use of
> > arbitrary precision.
>
> I agree.
>
> --
> Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.org/>
> 100% accessible validated (X)HTML - Blog: <http://www.vinc17.org/blog/>
> Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)
Vincent,
Not quite.
Clauses 3.4 through 3.7 define floating-point datasets &
formats that may be used for fixed or arbitrary precision
floating-point datatypes. And, clause 3.7 defines two
classes of arbitrary precision datatypes: Extended, which
are presumed to be available to either the implementation
or the language to provide higher precisions than were
available in 754-1985 & Extendable, which are designed
to give the programmer direct control over the range &
precision of both binary & decimal datatypes.
However, if by "arbitrary precision" you mean a sort of
variable precision arithmetic that takes one precision of
operands & returns a result whose precision is a function
of the operands then, yes, beyond conversions & FormatOf
operations 754-2008 has no such notion.
As for formats, both extended & extendable contain proper
subsets for which formats are defined. But the full set
of datatypes characterized by {radix x precision x range}
is available for those who wish to contrive formats of
their own.
In hindsight, we were lucky to get the sort of arbitrary
precision we have. :-)
Take care,
Dan