|LOG1P(3)||Linux Programmer's Manual||LOG1P(3)|
NAME¶log1p, log1pf, log1pl - logarithm of 1 plus argument
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)):
DESCRIPTION¶These functions return a value equivalent to
log (1 + 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: 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).
|log1p (), log1pf (), log1pl ()||Thread safety||MT-Safe|
CONFORMING TO¶C99, POSIX.1-2001, POSIX.1-2008.
BUGS¶Before version 2.22, the glibc implementation did not set errno to EDOM when a domain error occurred.
Before version 2.22, the glibc implementation did not set errno to ERANGE when a range error occurred.
SEE ALSO¶exp(3), expm1(3), log(3)
COLOPHON¶This page is part of release 5.02 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.