>perl -le"printf '%.20e', 38.91
3.89099999999999970000e+001

>perl -le"printf '%.20e', 38.91 * 100
3.89099999999999950000e+003

##</code><code>##

>perl -le"$n=38.91*100; $n=sprintf('%f',$n*1024)/1024; print $n%5;
1

##</code><code>##

>perl -le"$n=3891; print $n%5;
1