Log(1+x)
Synopsis:
#include <math.h>
double log1p ( double x );
float log1pf ( float x );
long double log1pl( long double x );
Arguments:
 x
 The number that you want to add 1 to and compute the natural log of.
Library:
libm
Use the l m option to
qcc
to link against this library.
Description:
The log1p(), log1pf(), and log1pl()
functions compute the value of
log(1+x),
where x > 1.0.
Returns:
log(1+x)
For finite values of x less than 1, these functions return NaN.
The return value when x is Inf is NaN.
Note:
If an error occurs, these functions return 0, but this is also a valid
mathematical result.
If you want to check for errors, set
errno
to 0, call the function, and then check
errno again.
These functions don't change
errno if no errors occurred.
Classification:
ANSI,
POSIX 1003.1
Safety: 

Cancellation point 
No 
Interrupt handler 
No 
Signal handler 
No 
Thread 
Yes 