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### 1.28 `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).