The expm1() function computes e^x-1.0.

If x is NaN, then the function returns NaN.

If x is positive infinity, expm1() returns positive infinity.

If x is negative infinity, expm1() returns -1.0.

If the value overflows, expm1() returns HUGE_VAL.

No errors will occur.

The value of expm1(x) may be more accurate than exp(x)-1.0 for small values of x.

The expm1() and log1p(3M) functions are useful for financial calculations of ((1+x)ⁿ-1)/x, namely:

expm1(n * log1p(x))/x

when x is very small (for example, when performing calculations with a small daily interest rate). These functions also simplify writing accurate inverse hyperbolic functions.

See attributes(5) for descriptions of the following attributes:

exp(3M), ilogb(3M), log1p(3M), attributes(5)