my @bigfloats = ([6, '1.234e56', '1e50'], [12, '2.3456e789', '1e777'], # "lorem ipsum ..."
                 [18, '3.45678e9012', '1e8994'], [36, '4.567890e12345', '1e12329']);
# Each of the above arrays has (0) the number of decimal digits of precision needed,
#                              (1) a number near the large end of the range for a type,
#                              (2) a number near epsilon for the sample number (1)
my $prec = 0;
foreach my $step (@bigfloats) {
    $prec = $step->[0];
    my $num = (0+$step->[1]);
    my $sum = ($num + $step->[2]);
    last unless $num eq $step->[1] and $sum > $num;
}
$defines .= ' -DLU_NV_PREC='.$prec;