log1p - Online Linux Manual Page

Section : 3
Updated : 2023-02-05
Source : Linux man-pages 6.03

NAME

log1p, log1pf, log1pl − logarithm of 1 plus argument

LIBRARY

Math library

(

libm

−lm

)

SYNOPSIS

#include <math.h>

double log1p(double

);

float log1pf(float

);

long double log1pl(long double

);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

log1p(

)

: _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

These functions return a value equivalent to

log (1 + x

)

The result is computed in a way that is accurate even if the value of x is near zero.

RETURN VALUE

On success, these functions return the natural logarithm of (1 + x)

If x is a NaN, a NaN is returned.

If x is positive infinity, positive infinity is returned.

If x is −1, a pole error occurs, and the functions return −

HUGE_VAL

−

HUGE_VALF

, or −

HUGE_VALL

, respectively.

If x is less than −1 (including negative infinity), a domain error occurs, and a NaN (not a number) is returned.

ERRORS

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

Domain error: x

is less than −1

errno is set to EDOM (but see BUGS). An invalid floating-point exception

(

FE_INVALID

)

is raised.

Pole error: x

is −1

errno is set to ERANGE (but see BUGS). A divide-by-zero floating-point exception

(

FE_DIVBYZERO

)

is raised.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface	Attribute	Value
log1p(), log1pf(), log1pl()	Thread safety	MT-Safe

STANDARDS

C99, POSIX.1-2001, POSIX.1-2008.

BUGS

Before glibc 2.22, the glibc implementation did not set errno to EDOM when a domain error occurred.

Before glibc 2.22, the glibc implementation did not set errno to ERANGE when a range error occurred.