presto-main/src/main/java/io/prestosql/operator/scalar/MathFunctions.java/MathFunctions/signDecimalLong
class MathFunctions:        @LiteralParameters({"p", "s"})
        @SqlType("decimal(1,0)")
        public static long signDecimalLong(@SqlType("decimal(p, s)") Slice num)
        {
            if (isZero(num)) {
                return 0;
            }
            else if (isNegative(num)) {
                return -1;
            }
            else {
                return 1;
            }
        }