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expm1(3) — Linux manual page

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

expm1(3)                 Library Functions Manualexpm1(3)

NAME top

       expm1, expm1f, expm1l - exponential minus 1

LIBRARY top

       Math library (libm,-lm)

SYNOPSIS top

#include <math.h>double expm1(doublex);float expm1f(floatx);long double expm1l(long doublex);   Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):expm1():           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L               || _XOPEN_SOURCE >= 500               || /* Since glibc 2.19: */ _DEFAULT_SOURCE               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCEexpm1f(),expm1l():           _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           exp(x) - 1       The result is computed in a way that is accurate even if the value       ofx is near zero—a case whereexp(x) - 1 would be inaccurate due       to subtraction of two numbers that are nearly equal.

RETURN VALUE top

       On success, these functions returnexp(x) - 1.       Ifx is a NaN, a NaN is returned.       Ifx is +0 (-0), +0 (-0) is returned.       Ifx is positive infinity, positive infinity is returned.       Ifx is negative infinity, -1 is returned.       If the result overflows, a range error occurs, and the functions       return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.

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:       Range error, overflowerrno is set toERANGE(but see BUGS).  An overflow              floating-point exception (FE_OVERFLOW) is raised.

ATTRIBUTES top

       For an explanation of the terms used in this section, seeattributes(7).       ┌──────────────────────────────────────┬───────────────┬─────────┐       │Interface│Attribute│Value│       ├──────────────────────────────────────┼───────────────┼─────────┤       │expm1(),expm1f(),expm1l()          │ Thread safety │ MT-Safe │       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

       C11, POSIX.1-2008.

HISTORY top

       C99, POSIX.1-2001.  BSD.

BUGS top

       Before glibc 2.17, on certain architectures (e.g., x86, but not       x86_64)expm1() raised a bogus underflow floating-point exception       for some large negativex values (where the function result       approaches -1).       Before approximately glibc 2.11,expm1() raised a bogus invalid       floating-point exception in addition to the expected overflow       exception, and returned a NaN instead of positive infinity, for       some large positivex values.       Before glibc 2.11, 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            2025-05-17expm1(3)

Pages that refer to this page:exp(3), log1p(3)

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