long double __far logl(long double x); (C99)
Returns the natural logarithm of x.
logl returns a Not-a-Number (NaN) and sets macro EDOM to global variable errno if x is negative.
If x is zero, it returns -∞ and sets macro ERANGE to global variable errno.
This function calculates the natural logarithm of x, i.e., logarithm with base e.