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libc.a reference
expm1
Syntax
 #include <math.h>
double expm1(double x);

Description
This function computes the value of e^x  1, the exponential of
x minus 1, where e is the base of the natural system of
logarithms, approximately 2.718281828. The result is more accurate than
exp(x)  1
for small values of x, where the latter method
would lose many significant digits.
Return Value
e raised to the power x, minus 1. If the value of x is
finite, but so large that its exponent would overflow a double
,
the return value is Inf
, and errno
is set to
ERANGE
. If x is either a positive or a negative infinity,
the result is either +Inf
or 1, respectively, and errno
is not changed. If x is a NaN
, the return value is
NaN
and errno
is set to EDOM
.
Portability