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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
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log1p(3) Library Functions Manual log1p(3)
log1p, log1pf, log1pl - logarithm of 1 plus argument
Math library (libm, -lm)
#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
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.
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.
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.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ log1p(), log1pf(), log1pl() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
C99, POSIX.1-2001.
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.
exp(3), expm1(3), log(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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[email protected]
Linux man-pages 6.15 2025-05-17 log1p(3)
Pages that refer to this page: expm1(3), log(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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