EXPM1(3) Library Functions Manual EXPM1(3)

expm1 expm1f expm1l — compute exponential functions

#include <math.h>

double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.

These functions shall compute ex -1.0.

An application wishing to check for error situations should set errno to zero and call (FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or (FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions return ex -1.0.

If the correct value would cause overflow, a range error shall occur and expm1 (), expm1f (), and expm1l () shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.

If x is NaN, a NaN shall be returned.

If x is ±0, ±0 shall be returned.

If x is -Inf, -1 shall be returned.

If x is +Inf, x shall be returned.

If x is subnormal, a range error may occur and x should be returned.

These functions shall fail if:

The result overflows. If the integer expression ( math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression ( math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall be raised.

These functions may fail if:

[MX] The value of x is subnormal.

If the integer expression ( math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression ( math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.

None.

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

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

expm1(n * log1p(x))/x

when x is very small (for example, when calculating small daily interest rates). These functions also simplify writing accurate inverse hyperbolic functions.

For IEEE Std 754-1985 , 709.8 < x implies expm1 ( x) has overflowed.

On error, the expressions ( math_errhandling & MATH_ERRNO) and ( math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

None.

None.

exp(3) , feclearexcept(3) , fetestexcept(3) , ilogb(3) , log1p(3)

XBD V1_chap04(7) , <math.h>

First released in Issue 4, Version 2.

Moved from X/OPEN UNIX extension to BASE.

The expm1f () and expm1l () functions are added for alignment with the ISO/IEC 9899:1999 (“ISO C99”) standard.

The expm1 () function is no longer marked as an extension.

The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 (“ISO C99”) standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 (“ISO C99”) standard are marked.

January 1, 2008 posix.fail