Re: Motion P1788/M0044:Constructors -- Voting Period begins - controlling rounding mode
On 2013-05-16 21:24:36 -0400, Lee Winter wrote:
> The above code fragment makes a very dangerous assumption, to wit, that the
> atof() function from the compiler library is round-safe, which means that
> all of the functions it calls must also be round-safe.. In my experience
> few implementations make that claim. And some of those that do make the
> claim are false.
See below.
On 2013-05-17 14:49:37 +0200, Vincent Lefevre wrote:
> On 2013-05-17 04:11:16 -0500, Ralph Baker Kearfott wrote:
> > Yes, I am aware of access to changing the rounding mode in modern
> > programming languages. What I was not aware of was that implementers
> > interpreted this to apply to text-to-interval conversions, and that
> > the text-to-interval conversion is done correctly from the point of
> > view of interval computations.
Ralph, I think the meant conversions between floating-point values
and text strings.
> Well, for string conversion, this is a bug. But all operations are
> concerned by bugs, even the basic arithmetic operations. See:
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34678
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37838
>
> For C's math.h functions, this is worse, as the ISO C standard doesn't
> require the rounding direction to be honored. You could only rely on
> QoI.
Oops, this should have been an answer to Lee Winter. The rounding
direction must be honor for conversions between floating-point values
and text strings.
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Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.net/>
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