Provided by: manpages-dev_3.35-0.1ubuntu1_all 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);

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

expm1(x) returns a value equivalent to

exp(x) - 1

It 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.

RETURNVALUE

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.

CONFORMINGTO

C99, POSIX.1-2001.

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.

SEEALSO

exp(3), log(3), log1p(3)

COLOPHON

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project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
pages/.

2010-09-12                                   EXPM1(3)