OpenEuphoria

Re: atom = problem?

• Posted by CChris <christian.cuvier at a?ricultur?.gouv.fr> Apr 28, 2008
• 810 views

Jeremy Cowgar wrote:
> 
> Can someone make the following code work?
> 
> }}}
<eucode>
> include misc.e
> 
> atom a
> a = tan(10.5)
> pretty_print(1, a, {0})
> printf(1, "\n%.60f\n", a)
> 
> if a = 1.8498999934219273466595723220962099730968475341796875 then
>     puts(1, "EQUAL\n")
> else
>     puts(1, "NOT EQUAL\n")
> end if
> </eucode>
{{{

> 
> The result I get here w/3.2 or 3.1.1 is:
> 
> $ exu test.e 
> 1.849899993
> 1.849899993421927346659572322096209973096847534179687500000000
> NOT EQUAL
> 
> I'm having problems with unit testing because of this.
> 
> Thanks!
> 
> --
> Jeremy Cowgar
> <a href="http://jeremy.cowgar.com">http://jeremy.cowgar.com</a>

You shouldn't use string conversion to compare atoms, because of the limited
precision of floating point numbers in hardware.
Use atom_to_float64() in machine.e instead to obtain a sequence of 8 bytes,
which is the internal representation of the number. Then comparing these
sequences of equal length becomes unambiguous.

CChris