NAME
log1p, log1pf, log1pl - logarithm of 1 plus argument
LIBRARY
Math library (libm, -lm)
SYNOPSIS
#include <math.h>double log1p(double \nx\n);\n
\nfloat log1pf(float \nx\n);\n
\nlong double log1pl(long double \nx\n);log1p\n():
\n
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
\n
|| _XOPEN_SOURCE >= 500
\n
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
\n
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCElog1pf(), log1pl():
\n
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
\n
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
\n
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCEDESCRIPTION
These functions return a value equivalent to
\n
log (1 + \nx\n)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
C11, POSIX.1-2008.
HISTORY
C99, POSIX.1-2001.
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)