table of contents
LOG1P(3) | Linux Programmer's Manual | 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():
or cc -std=c99
log1pf(), log1pl():
or cc -std=c99
DESCRIPTION¶
log1p(x) returns a value equivalent to
log (1 + x)
It 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
- An invalid floating-point exception (FE_INVALID) is raised.
- Pole error: x is -1
- A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.
These functions do not set errno.
CONFORMING TO¶
C99, POSIX.1-2001.
SEE ALSO¶
COLOPHON¶
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.
2010-09-20 |