Perl help

Stephen Ryan stephen.p.ryan at dartmouth.edu
Tue Jul 22 16:52:28 EDT 2003


On Tue, 2003-07-22 at 16:41, Stephen Ryan wrote:
> On Tue, 2003-07-22 at 16:36, Erik Price wrote:
> > Cole Tuininga wrote:
> > > Got a perl question for y'all.  I rarely have to do anything with perl,
> > > and I'm sure perl has a good reason for behaving like the following, but
> > > heck if I can figure it out.
> > > 
> > > The perl cookbook suggestions using sprintf for rounding floats.  This
> > > seemingly works fine:
> > > 
> > > egon at trogdor:~$ perl -e 'print sprintf( "%.2f\n", 0.562 )'
> > > 0.56
> > > egon at trogdor: perl -e 'print sprintf( "%.2f\n", 0.567 )'
> > > 0.57
> > > 
> > > However, I'm extremely confused by the following:
> > > 
> > > egon at trogdor:~$ perl -e 'print sprintf( "%.2f\n", 0.565 )'
> > > 0.56
> > 
> > I don't have an answer, Cole, but the same happens in Python and I'd bet 
> > in C as well -- must be a convention of the printf routines:
> > 
> > Python 2.2.2 (#1, Mar  9 2003, 08:18:26)
> > [GCC 3.2 20020927 (prerelease)] on cygwin
> > Type "help", "copyright", "credits" or "license" for more information.
> >  >>> print "%.2f\n" % 0.562
> > 0.56
> > 
> >  >>> print "%.2f\n" % 0.567
> > 0.57
> > 
> >  >>> print "%.2f\n" % 0.565
> > 0.56
> 
> 
> Aha!  Google for "round to even" -- it's an IEEE floating point
> computation rule.

Errm.  I take it back.

$ perl -e 'print sprintf( "%.2f\n", 0.575 )'
0.57

Dunno what's up with that.



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