1.36 log1p, log1pf—log of 1 + x

Synopsis

#include <math.h>
double log1p(double x);
float log1pf(float x);

Description
log1p calculates the natural logarithm of 1+x. You can use log1p rather than ‘log(1+x)’ for greater precision when x is very small.

log1pf calculates the same thing, but accepts and returns float values rather than double.

Returns
log1p returns a double, the natural log of 1+x. log1pf returns a float, the natural log of 1+x.

Portability
Neither log1p nor log1pf is required by ANSI C or by the System V Interface Definition (Issue 2).