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### 1.33 `log`, `logf`—natural logarithms

Synopsis

         #include <math.h>
         double log(double x);
         float logf(float x);

Description
Return the natural logarithm of x, that is, its logarithm base e (where e is the base of the natural system of logarithms, 2.71828...). `log` and `logf` are identical save for the return and argument types.

You can use the (non-ANSI) function `matherr` to specify error handling for these functions.

Returns
Normally, returns the calculated value. When x is zero, the returned value is `-HUGE_VAL` and `errno` is set to `ERANGE`. When x is negative, the returned value is NaN (not a number) and `errno` is set to `EDOM`. You can control the error behavior via `matherr`.

Portability
`log` is ANSI. `logf` is an extension.