Returns exp($num) - 1, computed in a way that is accurate even
when the value of number is close to zero
Description
floatexpm1(float$num)
expm1 returns the equivalent to
exp($num) - 1 computed in a way that is
accurate even if the value of num is near zero,
a case where exp($num) - 1 would be
inaccurate due to subtraction of two numbers that are nearly equal.