Man page - logl(3)

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Manual

log

NAME
LIBRARY
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
STANDARDS
HISTORY
BUGS
SEE ALSO

NAME

log, logf, logl - natural logarithmic function

LIBRARY

Math library ( libm , -lm )

SYNOPSIS

#include <math.h>

double log(double x );
float logf(float x );
long double logl(long double x );

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 <= 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).

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STANDARDS

C11, POSIX.1-2008.

HISTORY

C99, POSIX.1-2001.

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)