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);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
log1p(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or cc -std=c99 log1pf(), log1pl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99
DESCRIPTION
log1p(x) returns a value equivalent to
log (1 + x)
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. | |
CONFORMING TO
C99, POSIX.1-2001.
SEE ALSO
COLOPHON
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