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.
To check for error situations, use
feclearexcept()
and
fetestexcept():
 Call feclearexcept(FE_ALL_EXCEPT) before calling
log1p(), log1pf(), or log1pl().
 On return, if fetestexcept(FE_INVALID  FE_DIVBYZERO  FE_OVERFLOW  FE_UNDERFLOW)
is nonzero, then an error has occurred.
Returns:
log(1+x)
 If x is 1, a pole error occurs, and these functions return HUGE_VAL,
HUGE_VALF, and HUGE_VALL, respectively.
 For finite values of x that are less than 1, or if x is Inf,
a domain error occurs, and NaN is returned.
 If x is NaN, NaN is returned.
 If x is ±0, or +Inf, x is returned.
 If x is subnormal, a range error may occur, and x is returned.
Classification:
ANSI,
POSIX 1003.1
Safety: 

Cancellation point 
No 
Interrupt handler 
No 
Signal handler 
No 
Thread 
Yes 