develooper Front page | perl.perl5.porters | Postings from March 2019

[perl #120426] Strange and unwarranted underflow in string-to-number

From:
Karl Williamson via RT
Date:
March 25, 2019 19:56
Subject:
[perl #120426] Strange and unwarranted underflow in string-to-number
Message ID:
rt-4.0.24-20012-1553543772-706.120426-15-0@perl.org
On Wed, 25 Dec 2013 13:51:27 -0800, davem wrote:
> On Tue, Dec 03, 2013 at 01:31:27PM +0000, Dave Mitchell wrote:
> > On Mon, Dec 02, 2013 at 04:34:34PM +0000, Dave Mitchell wrote:
> > > On Mon, Dec 02, 2013 at 03:42:59PM +0000, Zefram wrote:
> > > > Dave Mitchell wrote:
> > > > > I fixed this by stopping the processing of the integer or
> > > > > fractional
> > > > > component once its been detected that only zeroes are left
> > > > > (with a
> > > > > suitable adjustment of the exponent).
> > > >
> > > > Eww.  That won't fix cases where the extra digits are non-zero,
> > > > such as
> > > >
> > > > $ echo 0.15301e-305 | perl -e '$v = <STDIN>; print "v=", $v + 0,
> > > > "\n";'
> > > > v=0
> > > > $ echo 0.15399e-305 | perl -e '$v = <STDIN>; print "v=", $v + 0,
> > > > "\n";'
> > > > v=0
> > >
> > >
> > > Oh yeah :-(
> > >
> > > I'll need to rethink that.
> >
> > Second attempt now smoking as smoke-me/davem/float1:
> >
> > commit 72cfc3028683d7d6428ee0b881a788aba667fe8e
> > Author:     David Mitchell <davem@iabyn.com>
> > AuthorDate: Mon Dec 2 15:04:49 2013 +0000
> > Commit:     David Mitchell <davem@iabyn.com>
> > CommitDate: Tue Dec 3 12:30:01 2013 +0000
> >
> > [perl #120426] atof() small value rounding errors
> >
> > For something like 0.153e-305, which is small, but not quite the
> > smallest
> > number (which is around 2.2e-308), adding extra digits to the
> > fractional par
> > could cause unnecessary rounding to zero.
> 
> Now in blead as b27804d8b48d647c08dc853b49e5b311fe166616.
> 
> This doesn't address comments that appeared further in this thread.

I looked through this ticket, and don't see any comments that haven't been addressed.  Please highlight those that haven't been addressed.  If none, we can close this ticket

-- 
Karl Williamson

---
via perlbug:  queue: perl5 status: open
https://rt.perl.org/Ticket/Display.html?id=120426



nntp.perl.org: Perl Programming lists via nntp and http.
Comments to Ask Bjørn Hansen at ask@perl.org | Group listing | About