log1p(), log1pf(), log1pl()

Updated: May 06, 2022

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 general-purpose math library.
libm-sve
(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:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in 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:

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 floating-point number.

Classification:

C11, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes