presto-main/src/main/java/io/prestosql/operator/scalar/MathFunctions.java/Truncate/truncateLongShort
class Truncate:        @LiteralParameters({"p", "s", "rp"})
        @SqlType("decimal(rp,0)")
        @Constraint(variable = "rp", expression = "max(1, p - s)")
        public static long truncateLongShort(@LiteralParameter("s") long numScale, @SqlType("decimal(p, s)") Slice num)
        {
            return unscaledDecimalToUnscaledLong(rescaleTruncate(num, -(int) numScale));
        }