$ perl -e'printf "%.20e\n", 1.255'
1.25499999999999989342e+00

$ perl -e'printf "%.20e\n", (1.255 * 100 + 0.5) * 10000000'
1.25999999999999976158e+09

##</code><code>##

int(1259999999.999999)              = 1259999999
int((1.255 * 100 + 0.5) * 10000000) = 1256000000

##</code><code>##

( $j = sprintf("%.6f", $j) ) =~ s/\..*//s;