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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
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expm1(3) Library Functions Manual expm1(3)
expm1, expm1f, expm1l - exponential minus 1
Math library (libm, -lm)
#include <math.h>
double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);
Feature Test Macro Requirements for glibc (see
feature_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_SOURCE
expm1f(), expm1l():
_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
exp(x) - 1
The result is computed in a way that is accurate even if the value
of x is near zero—a case where exp(x) - 1 would be inaccurate due
to subtraction of two numbers that are nearly equal.
On success, these functions return exp(x) - 1.
If x is a NaN, a NaN is returned.
If x is +0 (-0), +0 (-0) is returned.
If x is positive infinity, positive infinity is returned.
If x 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.
See math_error(7) for information on how to determine whether an
error has occurred when calling these functions.
The following errors can occur:
Range error, overflow
errno is set to ERANGE (but see BUGS). An overflow
floating-point exception (FE_OVERFLOW) is raised.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ expm1(), expm1f(), expm1l() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
C99, POSIX.1-2001. BSD.
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 negative x 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 positive x values.
Before glibc 2.11, the glibc implementation did not set errno to
ERANGE when a range error occurred.
exp(3), log(3), log1p(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⟩.
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-
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improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 expm1(3)
Pages that refer to this page: exp(3), log1p(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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