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

ANSI/ISO C	No
POSIX	No