EXPM1(3M) | Mathematical Library Functions | EXPM1(3M) |

c99 [flag... ]file...-lm[library... ] #include <math.h>doubleexpm1(doublex);

floatexpm1f(floatx);

long doubleexpm1l(long doublex);

These functions compute *e*^*x*−1.0.

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.

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.

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.

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE | ATTRIBUTE VALUE |

Interface Stability | Standard |

MT-Level | MT-Safe |

math.h(3HEAD), exp(3M), feclearexcept(3M), fetestexcept(3M), ilogb(3M), log1p(3M), attributes(7), standards(7)

July 12, 2006 | SunOS 5.11 |