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
 The generalpurpose math library.
 libmsve
 (QNX Neutrino 7.1 or later)
A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.
Your system requirements will determine how you should work with these libraries:
 If you want only selected processes to run with the SVE version, you can include both libraries in your OS image
and use the l m or l msve option to
qcc
to link explicitly against the appropriate one.
 If you want all processes to use the SVE version, include libmsve.so in your OS image
and set up a symbolic link from libm.so to libmsve.so.
Use the l m option to
qcc
to link against the library.
Note:
Compile your program with the fnobuiltin option to prevent the compiler from using a
builtin version of the function.
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().
For example:
 Call feclearexcept(FE_ALL_EXCEPT) before calling
log1p(), log1pf(), or log1pl().
 On return, if fetestexcept(FE_ALL_EXCEPT)
is nonzero, then an error has occurred.
Returns:
log(1+x)
If x is: 
These functions return: 
Errors: 
x is 1.0 
Inf 
FE_DIVBYZERO 
Less than 1.0 and finite, or Inf 
NaN 
FE_INVALID 
±0.0 
x 
— 
Inf 
Inf 
— 
NaN 
NaN 
— 
Subnormal 
x 
— 
These functions raise FE_INEXACT if the FPU reports that
the result can't be exactly represented as a floatingpoint number.
Classification:
C11,
POSIX 1003.1
Safety: 

Cancellation point 
No 
Interrupt handler 
Yes 
Signal handler 
Yes 
Thread 
Yes 