math.roundhalfdown
Available inall subroutines.
Rounds to nearest, ties towards negative infinity (also known as half down).
Return Value
If x is math.NAN, a NaN will be returned.
If x is integral, ±0, x itself is returned.
If x is math.POS_INFINITY or
math.NEG_INFINITY, an infinity
of the same sign is returned.
Otherwise, the rounded value of x is returned.