presto-main/src/main/java/io/prestosql/operator/scalar/MathFunctions.java/MathFunctions/log2
class MathFunctions:    @Description("logarithm to base 2")
    @ScalarFunction
    @SqlType(StandardTypes.DOUBLE)
    public static double log2(@SqlType(StandardTypes.DOUBLE) double num)
    {
        return Math.log(num) / Math.log(2);
    }