logl (3)

NAME

log, logf, logl - natural logarithmic function

SYNOPSIS

#include <math.h>
double log(double x);
float logf(float x);
long double logl(long double x);
Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
logf(), logl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

These functions return the natural logarithm of x.

RETURN VALUE

On success, these functions return the natural logarithm of x.
If x is a NaN, a NaN is returned.
If x is 1, the result is +0.
If x is positive infinity, positive infinity is returned.
If x is zero, then a pole error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.
If x is negative (including negative infinity), then 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 negative
errno is set to EDOM. An invalid floating-point exception (FE_INVALID) is raised.
Pole error: x is zero
errno is set to ERANGE. 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
log (), logf (), logl () Thread safety MT-Safe

CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.

BUGS

In glibc 2.5 and earlier, taking the log() of a NaN produces a bogus invalid floating-point (FE_INVALID) exception.

SEE ALSO

cbrt(3), clog(3), log10(3), log1p(3), log2(3), sqrt(3)

Information

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