"double expm1(double "x);
"float expm1f(float "x);
"long double expm1l(long double "x);
expm1(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.
BSD, C99. The float and the long double variants are C99 requirements.
exp(3), log(3), log1p(3)