expm1 - compute exponential functions
#include <math.h> double expm1 (double x);
The expm1() function computes ex-1.0.
If x is NaN, then the function returns NaN and errno may be set to EDOM.
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 and may set errno to ERANGE.
The expm1() function may fail if:
- The value of x is NaN.
- The result overflows.
The value of expm1(x) may be more accurate than exp(x)-1.0 for small values of x.
The expm1() and log1p() functions are useful for financial calculations of ((1+x)n-1)/x, namely:
when x is very small (for example, when calculating small daily interest rates). These functions also simplify writing accurate inverse hyperbolic functions.
- expm1(n * log1p(x))/x
exp(), ilogb(), log1p(), <math.h>.