# EXPM1(3) - man page online | library functions

Exponential minus 1.

Chapter

2015-04-19

EXPM1(3) Linux Programmer's Manual EXPM1(3)## NAME

expm1, expm1f, expm1l - exponential minus 1## SYNOPSIS

#include <math.h> double expm1(double x); float expm1f(float x); long double expm1l(long double x); Link with -lm. Feature Test Macro Requirements for glibc (see feature_test_macros(7)): expm1(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99 expm1f(), expm1l(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99## DESCRIPTION

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.## RETURN VALUE

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.## 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: Range error, overflow errno is set to ERANGE (but see BUGS). An overflow floating-point exception (FE_OVERFLOW) is raised.## ATTRIBUTES

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

C99, POSIX.1-2001, POSIX.1-2008.## BUGS

For some large negative x values (where the function result approaches -1), expm1() raises a bogus underflow floating-point exception. For some large positive x values, expm1() raises a bogus invalid floating-point exception in addition to the expected overflow exception, and returns a NaN instead of positive infinity. Before version 2.11, the glibc implementation did not set errno to ERANGE when a range error occurred.## SEE ALSO

exp(3), log(3), log1p(3)## COLOPHON

This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.2015-04-19 EXPM1(3)

This manual | Reference | Other manuals |

expm1(3) | referred by | log1p(3) |

refer to | attributes(7) | exp(3) | feature_test_macros(7) | log(3) | log1p(3) | math_error(7) |