**Use case**

Convert bitmask to position.
It would allow us to directly use FLAT dictionary or Enum datatype without jumping around slow `bitmasktoArray` and `arrayMap`

**Describe the solution you'd like**

```
SELECT
    arrayMap(x -> log2(x), bitmaskToArray(100)) AS bitmask,
    bitPositions(100)  AS bitpositions

┌─bitmask─┬─bitpositions─┐
│ [2,5,6] │ [2,5,6]      │
└─────────┴──────────────┘
```

{
        return (UInt64(unhex(pos[0])) << 20)
             | (UInt64(unhex(pos[1])) << 16)
             | (UInt64(unhex(pos[3])) << 12)
             | (UInt64(unhex(pos[4])) << 8)
             | (UInt64(unhex(pos[6])) << 4)
             | (UInt64(unhex(pos[7])));
    }
    static constexpr auto name = "MACStringToOUI";
};
template <typename Impl>
class FunctionMACStringTo : public IFunction
{
public:
    static constexpr auto name = Impl::name;
    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionMACStringTo<Impl>>(); }
    String getName() const override
    {
        return name;
    }
    size_t getNumberOfArguments() const override { return 1; }
    DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
    {
        if (!isString(arguments[0]))
            throw Exception("Illegal type " + arguments[0]->getName() + " of argument of function " + getName(),
            ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
        return std::make_shared<DataTypeUInt64>();
    }
    bool useDefaultImplementationForConstants() const override { return true; }