dt_fabsl
long double val = dt_fabsl((long double)datum);
long double f = (dt_fabsl((long double)val) * len) / total;
f = (dt_fabsl((long double)val) * len) / total;
f = (dt_fabsl((long double)val) * len) / total;
f = (dt_fabsl((long double)val) * len) / total;
val = dt_fabsl(datum * (len - 1)) / total;