use Math::BigFloat;;

$n = Math::BigFloat->new( '3.1415926535897932384626433832795' );;

$d = 0 + $n->bstr;;

printf "%.17f\n", $d;;
3.14159265358979310

$bfd = Math::BigFloat->new( sprintf "%.17f", $d );;
print $bfd;;
3.1415926535897931

$n -= $bfd;;
print $n;;
0.0000000000000001384626433832795