OpenEuphoria

RE: BUG! Erratic for loop behavior

• Posted by Chris Bensler <bensler at mail.com> Mar 23, 2002
• 509 views

Do a search for "floating point precision" in the mailing list archives.

Chris

Andy Serpa wrote:
> 
> Rolf Schröder wrote:
> > Andy Serpa wrote:
> > > ...
> > > ------------------------------
> > > for i = 31.1 to 34.2 by .1 do
> > >   ? i
> > > end for
> > > ------------------------------
> > > stops at 34.1 (!), NOT as expected.
> > >
> > Hi Andy,
> >
> > that's ok. Look at this:
> >
> >     for i = 31.1 to 34.1 by 0.1 do
> >         printf(1,"%20.15f\n",i)
> >     end for
> >
> > and you will notice why: the decimal given value 0.1 is exactly
> > representable in the computer for it has to stores it internally as an
> > binary value with a limited number of bits. Actually, 0.1 (dec.) is has
> > an unlimited binary representation: 0.0001100110011..... . This is the
> > correct way to do it (have in mind that 31.1 and 34.1 are also not
> > exactly representable!):
> >
> >     for i = 311 to 341 by 1 do
> >         printf(1,"%20.15f\n",i/10)
> >     end for
> >
> 
> Yeah, that's not really good enough for me -- .1 should be .1 in a loop.
>  The Euphoria manual even has an example under the FOR loop section
> using a .3 "by" value...  Is this also a "feature"?
> 
>