expm1

, expm1f

, expm1l

- compute exponential function

Synopsis

c99 [ flag... ] file... -lm [ library... ]
#include <math.h>

double expm1(double x);

float expm1f(float x);

long double expm1l(long double x);

Description

These functions compute e^x-1.0.

Return Values

Upon successful completion, these functions return e^x-1.0.

If x is NaN, a NaN is returned.

If x is ±0, ±0 is returned.

If x is -Inf, -1 is returned.

If x is +Inf, x is returned.

Errors

These functions will fail if:

Range Error

The result overflows.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the overflow floating-point exception is raised.

Usage

The value of expm1(x) can 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.

An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.

Attributes

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

See Also

exp(3M), feclearexcept(3M), fetestexcept(3M), ilogb(3M), log1p(3M), math.h(3HEAD), attributes(5), standards(5)