Another issue to consider... http://www.cygnus-software.com/papers/comparingfloats/Comparing%20floating%20point%20numbers.htm#_Toc135149458
-J
--
On Tue, Jul 31, 2007 at 08:46:41AM -1000, Joshua Hoblitt wrote:
> A couple of comments on dealing with floats.
>
> - Use FLT_EPSILON/DBL_EPSILON from float.h
>
> - You method is total overkill, return (fabs(x - y) < DBL_EPSILON ? 1 : 0);
> should be sufficent (note: check with a numerical expert).
>
> - What about NANs and INFs? I typical test for one of the values being
> NAN but allow INFs to be compared.
>
>
> -J
>
> --
> On Tue, Jul 31, 2007 at 07:17:15PM +0200, Paul Cochrane wrote:
> > Hi all,
> >
> > I'm wanting to remove all the floating point comparison warnings which
> > appear when compiling parrot and wanted some advice as to how best to
> > achieve this.
> >
> > Floating point comparisons appear in code such as (taken from src/string.c):
> >
> > if (*p == '-' && f == 0.0)
> >
> > I'd like to replace this with
> >
> > if (*p == '-' && is_float_equal(f, 0.0))
> >
> > where
> >
> > #define EPSILON 0.0000005
> >
> > INTVAL is_float_equal(FLOATVAL x, FLOATVAL y)
> > {
> > return (fabs(x - y) <= fabs(x + y)*EPSILON) ? 1 : 0;
> > }
> >
> > (this code was adapted from equivalent fortran code given here:
> > http://www.lahey.com/float.htm courtesy of particle++).
> >
> > Is this a good way to achieve the goal of safe floating point
> > comparisons? The #define and function need to go somewhere. Where
> > exactly? And which header gets the declaration? parrot.h? Is there
> > a better way to do this? Could/should I be using a macro instead?
> >
> > Thanks heaps in advance!
> >
> > Paul
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