AbsInt returns the absolute value of integer x.
Note that when x is math.MinInt32 (or -2147483648), the same
negative value is returned since there is no 'signed' int 2147483648.
AbsInt64 returns the absolute value of 64-bit integer x.
Note that when x is math.MinInt (or -9223372036854775808), the same
negative value is returned since there is no 'signed' int64 9223372036854775808.