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log1p(3) — Linux manual page

NAME \|LIBRARY \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|ATTRIBUTES \|STANDARDS \|HISTORY \|BUGS \|SEE ALSO \|COLOPHON

log1p(3)                 Library Functions Manuallog1p(3)

NAME top

       log1p, log1pf, log1pl -  logarithm of 1 plus argument

LIBRARY top

       Math library (libm,-lm)

SYNOPSIS top

#include <math.h>double log1p(doublex);float log1pf(floatx);long double log1pl(long doublex);   Feature Test Macro Requirements for glibc (seefeature_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_SOURCElog1pf(),log1pl():           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L               || /* Since glibc 2.19: */ _DEFAULT_SOURCE               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION top

       These functions return a value equivalent to           log(1 +x)       The result is computed in a way that is accurate even if the value       ofx is near zero.

RETURN VALUE top

       On success, these functions return the natural logarithm of(1 + x).       Ifx is a NaN, a NaN is returned.       Ifx is positive infinity, positive infinity is returned.       Ifx is -1, a pole error occurs, and the functions return       -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.       Ifx is less than -1 (including negative infinity), a domain error       occurs, and a NaN (not a number) is returned.

ERRORS top

       Seemath_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 toEDOM(but see BUGS).  An invalid floating-              point exception (FE_INVALID) is raised.       Pole error:x is -1.errno is set toERANGE(but see BUGS).  A divide-by-zero              floating-point exception (FE_DIVBYZERO) is raised.

ATTRIBUTES top

       For an explanation of the terms used in this section, seeattributes(7).       ┌──────────────────────────────────────┬───────────────┬─────────┐       │Interface│Attribute│Value│       ├──────────────────────────────────────┼───────────────┼─────────┤       │log1p(),log1pf(),log1pl()          │ Thread safety │ MT-Safe │       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

       C11, POSIX.1-2008.

HISTORY top

       C99, POSIX.1-2001.

BUGS top

       Before glibc 2.22, the glibc implementation did not seterrno toEDOMwhen a domain error occurred.       Before glibc 2.22, the glibc implementation did not seterrno toERANGEwhen a range error occurred.

COLOPHON top

       This page is part of theman-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⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       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-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17log1p(3)

Pages that refer to this page:expm1(3), log(3)

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