Re: Motion 46: finalise interval literals, amendments

[Ralph Baker Kearfott <rbk5287@xxxxxxxxxxxxx>]

Ned,

See "****==>" in the appended excerpt from 754-2008.

Doesn't this say that directed roundings shall be available?

Baker

================================================================
* 5.4.2 Conversion operations for floating-point formats and decimal 
character sequences

* 5.12 Details of conversion between floating-point data and external 
character
sequences 5.120

This clause specifies conversions between supported formats and external 
character sequences. Note that
conversions between supported formats of different radices are correctly 
rounded and set exceptions
correctly as described in 5.4.2, subject to limits stated in 5.12.2 below.

Implementations shall provide conversions between each supported binary 
format and external decimal
character sequences such that, under roundTiesToEven, conversion from 
the supported format to external
decimal character sequence and back recovers the original floating-point 
representation, except that a
signaling NaN might be converted to a quiet NaN. See 5.12.1 and 5.12.2 
for details.
Implementations shall provide exact conversions from each supported 
decimal format to external decimal
character sequences, and shall provide conversions back that recover the 
original floating-point
representation, except that a signaling NaN might be converted to a 
quiet NaN. See 5.12.1 and 5.12.2 for
details.

Implementations shall provide exact conversions from each supported 
binary format to external character
sequences representing numbers with hexadecimal digits for the 
significand, and shall provide conversions
back that recover the original floating-point representation, except 
that a signaling NaN might be converted
to a quiet NaN. See 5.12.1 and 5.12.3 for details.

* 5.12.2 External decimal character sequences representing finite numbers
5.12 .0
An implementation shall provide operations that convert from all 
supported floating-point formats to
external decimal character sequences (see 5.4.2). For finite numbers, 
these operations can be thought of as
parameterized by the source format, the number of significant digits in 
the result (if specified), and whether
the quantum is preserved (for decimal formats). Note that specifying the 
number of significant digits and
specifying quantum preservation are mutually incompatible. The means of 
specifying the number of
significant digits and of specifying quantum preservation are 
language-defined and are typically embodied
in the conversionSpecification of 5.4.2.

An implementation shall also provide operations that convert external 
decimal character sequences to all
supported formats. These operations can be thought of as parameterized 
by the result format.


****==> Within the limits stated in this clause, conversions in both 
directions shall preserve the value of a number
unless rounding is necessary and shall preserve its sign. If rounding is 
necessary, they shall use correct
rounding and shall correctly signal the inexact and other exceptions.

All conversions from external character sequences to supported decimal 
formats shall preserve the quantum
(see 5.4.2) unless rounding is necessary. At least one conversion from 
each supported decimal format shall
preserve the quantum as well as the value and sign.

================================================================


On 07/04/2013 01:26 PM, Ned Nedialkov wrote:
> On 2013-07-04, at 6:24 PM, "J. Wolff von Gudenberg" <wolff@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> > John,
> >   here is my second part of the comment on motion 46
> >
> >
> >   If the underlying type is IEEE754 conformant and provides the covertFormat function with rounding,
> I should check this myself, but I don't recall IEEE requiring directed roundings when converting a string
> to say double.


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---------------------------------------------------------------
R. Baker Kearfott,    rbk@xxxxxxxxxxxxx   (337) 482-5346 (fax)
(337) 482-5270 (work)                     (337) 993-1827 (home)
URL: http://interval.louisiana.edu/kearfott.html
Department of Mathematics, University of Louisiana at Lafayette
(Room 217 Maxim D. Doucet Hall, 1403 Johnston Street)
Box 4-1010, Lafayette, LA 70504-1010, USA
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