log1p (3)

NAME

log1p, log1pf, log1pl - logarithm of 1 plus argument

SYNOPSIS

#include <math.h>
double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);

Link with -lm.

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 versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
 
log1pf(), log1pl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 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

CONFORMING TO

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

BUGS

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

SEE ALSO

exp(3), expm1(3), log(3)

Information

Source
Linux kernel
OS/version
Source updated
September 15, 2017
Page created
February 9, 2018
Page generated
December 2, 2018