[ic] [interchange-bugs] [rt.icdevgroup.org #349] Vend::Util::round_to_frac_digits() simplification

[Mike Heins]

Quoting Peter (peter at pajamian.dhs.org):
> On 20/03/12 13:59, Mike Heins wrote:
> > Quoting Peter (peter at pajamian.dhs.org):
> >> CCing the userlist because I want Mike to see this.
> >>
> >> On 20/03/12 04:47, Anonymous via RT wrote:
> >>> round_to_frac_digits()  produces ".00" when called with (0, 2).  It
> >>> also parses the integers incorrectly: in normal Perl "1." is a valid
> >>> number, as is "+3", but "-" is not valid.
> >>>
> >>> Nearly all of the function logic can be replaced with:
> >>>
> >>> printf "%.*f", $digist, $num;
> >>
> >> Agreed, except it needs to be sprintf.
> >>
> >> Mike, is there any reason to not make this change?
> > 
> > Absolutely. Sprintf doesn't really round.
> 
> It does, but there are floating point errors in the rounding:
> 
> Correct:
> $ perl -le 'print sprintf "%.*f", 2, 0.124'
> 0.12
> $ perl -le 'print sprintf "%.*f", 2, 0.135'
> 0.14
> $ perl -le 'print sprintf "%.*f", 2, -0.124'
> -0.12
> $ perl -le 'print sprintf "%.*f", 2, -0.135'
> -0.14
> 
> Wrong (due to floating point errors):
> $ perl -le 'print sprintf "%.*f", 2, 0.125'
> 0.12
> $ perl -le 'print sprintf "%.*f", 2, -0.125'
> -0.12
> 
> We could compensate for those floating point errors like this:
> $ perl -le 'print sprintf "%.*f", 2, 0.125 * 1.000000000001'
> 0.13
> $ perl -le 'print sprintf "%.*f", 2, -0.125 * 1.000000000001'
> -0.13

Do:

	perldoc -q round

to see why I did it that way...we should just fix what
problems there are.

-- 
Mike Heins
Perusion -- Expert Interchange Consulting    http://www.perusion.com/
phone +1.765.253.4194  <mike at perusion.com>

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