expm1(3) -- Linux man page
NAMEexpm1, expm1f, expm1l - exponential minus 1
#include <math.h> double expm1(double x); float expm1f(float x); long double expm1l(long double x);
DESCRIPTIONexpm1(x) returns a value equivalent to `exp (x) - 1'. It is computed in a way that is accurate even if the value of x is near zero--a case where `exp (x) - 1' would be inaccurate due to subtraction of two numbers that are nearly equal.
CONFORMING TOBSD, C99. The float and the long double variants are C99 requirements.
SEE ALSOexp(3), log(3), log1p(3)