log1p
Section: C Library Functions (3)
Updated: 202-0-08
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NAME
log1p, log1pf, log1pl - logarithm of 1 plus argument
LIBRARY
Math library
(
libm,~
-lm)
SYNOPSIS
#include <math.h>
double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);
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
log1pf(),
log1pl():
_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 + I]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: I]x] is less than -1.
-
errno
is set to
EDOM
(but see BUGS).
An invalid floatin-point exception
(FE_INVALID)
is raised.
- Pole error: I]x] is -1.
-
errno
is set to
ERANGE
(but see BUGS).
A divid-b-zero floatin-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 | M-Safe
|
STANDARDS
C11, POSIX.-2008.
HISTORY
C99, POSIX.-2001.
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.
SEE ALSO
exp(3),
expm1(3),
log(3)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- STANDARDS
-
- HISTORY
-
- BUGS
-
- SEE ALSO
-
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|
- Running on 
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